Focus Meeting 3 - Poster Abstracts


AGN activity and the galaxy group environment

Khosroshahi, Habib

We study the AGN activity in the most massive galaxies in galaxy groups and show that their activity is influenced by the environment, more specifically with the dynamical state of the galaxy group. The dynamical state of the group is defined by the halo relaxation, probed by the stellar dominance of the brightest group galaxy and the offset between the position of the brightest group galaxy and the luminosity centroid of the group. We use GAMA survey data and show that the radio luminosity of the most massive galaxy in the group strongly depends on its environment, such that the brightest group galaxies in dynamically young or recently formed groups are an order of magnitude more luminous in the radio than those with a similar stellar mass but residing in dynamically old or early formed groups. We have been able to successfully reproduce such an environmental influence on AGN activity of giant elliptical galaxies using a newly developed semi-analytic galaxy formation model.

Proposed VLBI Observations in the FAST Commissioning Stage

Zhang, Haiyan

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is a Chinese mega science project, and the main structure of the telescope had been completed in September 2016. Now the FAST is in the commissioning stage._x000D_ As the most sensitive single-dish radio telescope, Very Long Baseline Interferometry (VLBI) research with FAST is one of the key goals. Due to its extremely collecting area and the location, FAST will greatly improve the sensitivity of VLBI observations, and detect more weak radio sources than ever before. For instance, if FAST joins into the European VLBI Network (EVN), the image sensitivity will be increased to 4.5 uJy/beam. Several scientific goals have been proposed for FAST VLBI observations, such as compact radio sources survey, and study the physical mechanism of Active Galactic Nuclei (AGNs); pulsar Astrometry, radio stars etc._x000D_ However, the complexity and the innovative nature of the FAST systems pose many challenges. The observations in draft–scan mode have been proposed to avoid the complex scan patterns and fast driving/switching of the telescope. Several new pulsars have been detected by FAST successfully recently._x000D_ For VLBI test observation with FAST, the objective is to establish VLBI observation system and detect the first VLBI fringe. In the commissioning stage, several adjustment and early sciences goals have been considered, such as observing calibrators to detect the first fringe, detecting strong OH and HI maser sources etc. Till now, the FAST VLBI backend using ROACH2 board has been developed and tested in the laboratory. The disk-based Mark 6 has also been built to record the observing data. The first VLBI fringe of FAST is expected in 2018.

What the iMOGABA tells us about Gamma-ray bright AGNs

Lee, Sang-Sung

The interferometric monitoring of gamma-ray bright AGNs (iMOGABA) program aims at revealing the origins of the gamma-ray flares that are often detected in active galactic nuclei (AGNs). We would like to talk about what we have learned about the Gamma-ray bright AGNs based on the recent results of the Korean VLBI Network Key Science Program: the iMGOABA. The results will include a) the source properties of the whole samples obtained from a single-epoch observation, and b) some of scientific highlights for the iMOGAGBA on specific sources. From those highlighted works, we find that the Gamma-ray bright AGNs become fainter at higher frequencies, yielding optically thin spectra at mm wavelengths. Based on the studies on specific sources, taking into account the synchrotron self-absorption model of the relativistic jet, we are able to estimate the magnetic field strength in the mas emission region during the observing period. More scientific highlights and future prospects of the KVN KSP are discussed.

Radio Properties of AGN in the GAMA 23 Field

Leahy, Denis

The GAMA 23 Field, a region of about 6 degrees by 7degrees, was observed by the Australia Square Kilometer Array Pathfinder (ASKAP) during its commissioning phase. We utilize the radio data from ASKAP in conjuntion with the optical data from the GAMA survey, and infrared data from the WISE survey to investigate the properties of AGN over this large field. A number of well-known properties of the AGN population are confirmed but we find some new properties because of the large area and sensitivity of the radio and optical data, which allows low mass galaxies to be identified out to a redshift of about 0.5.

Vortex - multiface unity of astrophysical objects

Matveyenko, Leonid

The fine structure of AGN objects (3C 84, 3C345, 3C454, OJ 287, Cyg A et al.), galaxy NGC 4258 and star formation region of Orion KL at maser emission had been investigated. The structure and cinematics correspond to vortex nature. The matter transferred to the nozzle, an angular momentum is caring away by a bipolar out flower. The ejection velocity is v < 0.1c. The rest of the matter drops out on the forming central massive body. The rotation collimated and accelerated streams, generated ring currents – magnetic fields. The gravitation and magnetic fields extra accelerated and stabilized the structure. The jet moved along the magnetic field - accelerated, the counter jet against – deaccelerated, that determined extra emission of relativistic electrons. The brightness temperature of the nozzles 1013=Tb=1014 K. Bipolar out flower of Cyg A surrounding by low velocity one. A Seifert galaxy 3C 84 is double gravity connected system. In blazar OJ 287 formatted new independent whirlwind. In the Orion KL a matter transferred along two spiral arms to the nozzle. An excess angular momentum is caring away by a bipolar out flower that determined rigid-body rotation. The rotation collimated and accelerated streams. The gravitational field of the central body accelerated and stabilized the structure. Bipolar high velocity spiral out flower of surrounded by two low velocity ones. The structure and cinematics of Orion KL is vortex. The matter transferred along arms to the nozzle and ejected by bipolar out flowers, that determined rigid-body rotation of central part of a disk ? =15 A.U. The period rotation is 170 years. An instability of the outflow caused precession – the spiral structure. Remain of the medium drops on the central body. Rotation of the out flower collimated and accelerated of the out flowers. The ejection velocity v˜5 km/s, which accelerated until 45 km/s at distance 2AU. The objects are self-organized structures, which correspond to gas dynamic solutions.

Relativistic beaming effect and radio dominance of Fermi sources.

Pei, Zhi-Yuan

Active Galactic Nuclei are very interesting and attractive objects for researching in extragalactic sources. A small subset of the radio loud AGNs is called blazars, which display extreme observational properties, such as  showing ?-ray radiation, rapid variability, high luminosity, high and variable polarization, and superluminal motion. All of those observational properties are probably due to a relativistic beaming effect with the jet pointing close to the line of sight. Blazars also have two subclasses, namely BL Lac and FSRQ. Observations suggest that the orientation can be expressed by a core-dominance parameter R,  which defined asR = Score/Sext. ,where Score and Sext. stands for the emission in the core Sext.component and extended component, respectively. The R, to some extent, is associated with the beaming effect. After the launch of Fermi Large Area Telescope(Fermi LAT), many sources have been detected to show high energetic ?-ray emission. In the latest catalogue(3FGL), 1444 sources are added by the former ones, and now are up to over 3000 sources, in which around 60% are AGNs, and 98% are Fermi blazars. Those data has give us a good opportunity to study the high energy astrophysics and beaming effect. In this work, we collected relevant observations from the literature for a sample of 2013 AGNs including 240 Fermi-detected sources and 1173 non- Fermi-detected sources. We found that the mean value of core dominance parameter for Fermi sources is higher than the case for non- Fermi sources, however, in contrary, the mean value of radio spectral index for Fermi sources is lower than the case for non-Fermi sources. A sequence is shown that: BL Lac > quasar > Seyfert > galaxy > FR type galaxy. For both ?-ray spectral index and variability index, quasar is higher than BL Lac. Meanwhile, We found that the core-dominance parameter-spectral index correlation exists for a large sample presented in this work, which may come from a relativistic beaming effect. 


Zhdanov, Valery

The profiles of relativistic lines in the X-ray spectra of active galactic nuclei (AGN) contain important information about the AGN "central machine". If AGN is the source of a gravitational lens system with microlensing events, additional data can be obtained about both the accretion disk around the central black hole and the parameters of the local lens mapping. We performed simulations of the microlensed lines formed in the thin accretion disk during the High Amplification Events. Several models of the accretion disk structure and approximations concerning the the local lens mapping are discussed. We have shown that the time dependence of the line profiles depends strongly on the caustic orientation with respect to the disk, which makes it possible to estimate this orientation along with the distribution of the line intensity over the disk.

Multi-frequency study of a large sample of double-double radio galaxies

Nandi, Sumana

Striking examples of episodic jet activity in active galactic nuclei (AGN) are the double-double radio galaxies (DDRGs) with two pairs of lobes emerging from the same central engine. The mechanism for multiple jet activity in DDRGs is still unclear. Several ideas were proposed to explain this phenomenon and most possible scenario is merging of the two black holes. The number of DDRGs reported so far is very limited, and it is important to identify more of these to provide a significant statistical overview of the conditions to trigger the jets and the role of jets in terms of feedback mechanisms that affect the host galaxies. A significant number of smaller sized candidate DDRGs have been identified in our recent study. We started low-frequency observation of this sample to confirm that the sources are related to distinct epochs of nuclear activity. For few sources in this sample we noticed instability in jet direction. Radio galaxies with rapid change of jet axis are the prime candidates to detect binary black hole systems. Interestingly we identified one candidate which shows not only restarted jet activity with a axis reorientation but also generates double-peaked emissions line from the central AGN. The split in emission lines are the possible out come of a bound pair of supermassive black hole, moving with their own characteristic velocity. Here, I will highlight the main results from our observations and discuss on the possible scenarios responsible for the episodic activity in DDRGs.

The High-redshift Clusters Occupied by Bent Radio AGN (COBRA) Survey: The Spitzer Catalog

Paterno-Mahler, Rachel

We present 190 galaxy cluster candidates (most at high redshift) based on galaxy overdensity measurements in the Spitzer/IRAC imaging of the fields surrounding 646 bent, double-lobed radio sources drawn from the Clusters Occupied by Bent Radio AGN (COBRA) Survey. The COBRA sources were chosen as objects in the Very Large Array FIRST survey that lack optical counterparts in the Sloan Digital Sky Survey to a limit of m r = 22, making them likely to lie at high redshift. This is confirmed by our observations: the redshift distribution of COBRA sources with estimated redshifts peaks near z = 1 and extends out to z≈ 3. Cluster candidates were identified by comparing our target fields to a background field and searching for statistically significant (≥2σ ) excesses in the galaxy number counts surrounding the radio sources; 190 fields satisfy the ≥2σ limit. We find that 530 fields (82.0%) have a net positive excess of galaxies surrounding the radio source. Many of the fields with positive excesses but below the 2σ cutoff are likely to be galaxy groups. Forty-one COBRA sources are quasars with known spectroscopic redshifts, which may be tracers of some of the most distant clusters known.

New evidences for the North Polar Spur as the kpc-scale jet with extended cocoon

Miroshnichenko, Alla

The analysis of the jet hypothesis for the North Polar Spur as the Galaxy jet with extended cocoon is carried out. Befor we have derived the main physical parameters (the magnetic field strength, the spectral index, the radio luminosity, the jet propagation velocity, the characteristic age) of the North Polar Spur at the base of observed Galactic background at the low-frequency band. For the further testing of the jet hypothesis we derive some additional estimates, including the value of the mass accretion rate for the supermassive black hole at the Galactic centre and the value of the total energy of the North Polar Spur. We consider that the observed Galactic radio background is, in the main, the radio emission of extended cocoons of both possible Galactic jets (the North Polar Spur (jet) and the South spur (counterjet)). We have examined the features of the possible Galactic kpc-scale jet with extended cocoon and known kpc-scale Galactic winds and superbubbles.

Radio Galaxy Zoo: mapping AGN evolution via radio galaxy morphologies

Wong, O. Ivy

Visual inspection remains the primary method for extended radio morphology classification. Statistically-significant sample sizes of radio morphologies are required to further our understanding of radio AGN evolution. Radio Galaxy Zoo is an online citizen science project that enlists the help of the public to cross-match radio sources from the Faint Images of the Radio Sky at Twenty Centimeters (FIRST) and the Australia Telescope Large Area Survey (ATLAS) surveys, to host galaxies observed in the infrared images from the Wide-field Infrared Survey Explorer (WISE) and the Spitzer Space Telescope at 3.6 microns. The project is currently 75% complete. I will present a summary of recent results and the upcoming data release of ~75,000 radio sources. Despite using decades-old archival datasets, we have made new discoveries of rare classes of radio AGN that are useful for constraining the physical processes associated with radio jet formation and evolution (Banfield et al 2016, Kapińska et al 2017). Radio Galaxy Zoo is also collaborating with several international machine learning teams in the use of our catalogues as training sets for developing advanced deep learning algorithms that will benefit the upcoming pre-SKA surveys from which we expect tens of millions of radio sources._x000D_ (References: Banfield, Wong et al 2015 MNRAS, 453, 2326; Banfield et al 2016 MNRAS, 460, 2376; Contigiani et al 2017 MNRAS, 472, 636; Kapińska et al 2017 AJ, 154, 253; Lukic et al 2018, in press MNRAS)

Morphological study of a large sample of extragalactic radio sources for revelation of radio jets

Mickaelian, Areg

With an improved cross-correlation technique, we have matched two largest radio catalogs at 1.4 GHz (21 cm), NVSS and FIRST to improve positions and photometry, to reveal radio variability and check with optical variability, to study the radio structure and optical morphology of sources, to classify radio sources into FRI and FRII types, and to reveal jets and additional features. NVSS (Condon et al. 1998) contains 1,773,484 sources and FIRST (Helfand et al. 2015) contains 946,432 sources and have better positional and photometric accuracy (5 arcsec and 1 mJy, respectively). As a preliminary result, we obtained 556,282 common sources. 6301 of them show obvious signs of variability having > 50 mJy differences between fluxes in NVSS and FIRST. For these sources we have made multiwavelength (MW) investigations in all wavelength ranges aimed at finding relations between the radiation fluxes in different bands for different types of sources (blazars, QSOs, other AGN, and starbursts). Another possibility that appeared after having cross-correlated NVSS/FIRST sources, is the study of radio morphology. Given that FIRST resolution is higher, very often we have 2-4 FIRST associations within 30 arcsec corresponding to 1 NVSS source. In such cases the central source is considered as the core, and 2 farther bright sources are considered as radio lobes. Depending on the flux ratio of the central source and the lobes, we have preliminarily classified sources to FRI and FRII. On the other hand, the 4th component, when available, may be regarded as a jet, and very often it appears not far from the core. We match these results with radio contours to verify candidate jets, as well as we check these sources for radio variability. We identify NVSS/FIRST sources having 4 FIRST components and radio variability, a highly reliable sample for revelation of radio jets.


Bochkarev, Nikolai

We use our 10-20 year long spectral and photometric observations of optical variability for investigations of the physics and kinematics of AGN central parts, i.e. the emission regions which are close to the super-massive black hole. Here we give an overview of the results of our analysis of AGN optical spectral variability in a sample of AGNs with broad emission lines including radio-laud ones.

Laboratory simulation of astrophysical jets within facilities of Plasma Focus type

Beskin, Vasily

A laboratory simulation of astrophysical processes is one of the intensively developed areas of plasma physics. A new series of experiments has been launched recently on the Plasma Focus type facility in NRC Kurchatov Institute. The main goal is to study the mechanisms of the jet stabilization, due to which it can propagate at distances much greater than their transverse dimensions. The experiments with stationary gas filling revealed regimes in which a narrowly collimated plasma jet was formed, the head of which was no wider than several centimeters at jet propagation distances of up to 100 cm. The PF-1000 (IFPiLM, Warsaw, Poland) and KPF-4 (SFTI, Sukhum, Abkhazia) experiments are aimed at creating profiled initial gas distributions to control the conditions of plasma jet propagation in the ambient plasma. Estimations of the dimensionless parameters, i.e. the Mach, Reynolds, and Peclet numbers which were achieved during the experiments, showed that the PF-facilities can be used for the YSO jets modelling. Thefuture experiments, which can allow one to understand the nature of the stable plasma ejections observed in many astrophysical sources, are discussed.

The mass-metallicity relation of high-z type-2 AGNs

Matsuoka, Kenta

Metallicity is one of the most important clues in understanding the galaxy evolution since metal formations and its enrichments are closely connected with the past star formations in galaxies. The early-recognized relationship between galaxies and their metal contents would be the mass-metallicity relation (MZR), and this correlation has been explored at high redshift (z < 3) by active and earnest near-infrared (IR) observations. However, it should be more challenging to examine the MZR for higher-z galaxies (z > 3.5) since emission lines for metallicity diagnostics shift out of the K-band atmospheric window. Thus, we focus on active galactic nuclei (AGNs) instead of star-forming galaxies. Thanks to their huge luminosity and various emission lines in the wide wavelength range from ultraviolet (UV) to IR, we can easily measure metallicities even in the high-z universe.In this study, we investigated the MZR of type-2 AGNs at 1.2 < z < 4.0 by using high-z radio galaxies (HzRGs) and X-ray selected AGNs. To estimate narrow-line region (NLR) metallicities, we utilized type-2 AGNs of which rest-frame UV emission lines, i.e., CIV, HeII, and CIII], are available. From literature, we collected 67 HzRGs and 13 X-ray selected AGNs as type-2 AGNs, that a few of the later are newly observed with the Subaru Telescope. Furthermore, for 28 of them, we obtained host stellar masses estimated by spectral energy distribution fit: they cover the mass range of 10 < logM/M_Sun < 12. We divided 28 objects into three subsamples with stellar mass bins and estimated their NLR metallicities with a diagnostic diagram of CIV/HeII and CIII]/CIV. In the result, we found that there is a significant positive correlation between stellar masses and NLR metallicities in type-2 AGNs at 1.2 < z < 4.0. This is the first direct evidence that AGN metallicities are related to their host properties. In this meeting, we will present our new results described above and discuss the MZR of type-2 AGNs.

An interferometric quest to reveal the true nature of the core in the radio galaxy 3C 411

Perger, Krisztina

Examination of the X-ray spectrum of the classical double-lobed radio galaxy 3C 411 (PKS J2022+1001) resulted in two equally well-fitting models (Bostrom et al., 2014). One of the models was consistent with those known for radio galaxies, but the other one was a combination of two components: one similar to those found for Seyfert nuclei and another blazar-like, hard X-ray component. We investigated the parsec-scale radio structure of the galaxy core with sub-milliarcsec resolution very long baseline interferometry (VLBI) imaging, using archival Very Long Baseline Array (VLBA) data and new European VLBI Network (EVN) observations at multiple frequencies. The data do not confirm the presence of a blazar-like nucleus in the radio galaxy, and provide evidence for a change in the jet inclination angle with respect to the line of sight between pc and 100 kpc scales.

The location of the gamma-ray emitting region in blazars

Wu, Qingwen

The core-shift effect can be resoved at pc-scale for many blazars with radio VLBI observations. The equapartition magnetic field distribution can be derived along the jet. We model the simultaneous or quasi-simultaneous multi-band spectral energy distributions (SEDs) for a sample of blazars with a one-zone leptonic model and Markov chain Monte Carlo technique, where the core shift effects of these sources have been measured. Assuming the magnetic field strength in the γ-ray emitting region as constrained from the SED fitting follows the magnetic field distribution as derived from the radio core-shift measurements, we then can derive the location of the gamma-ray emitting region for these blazars. We find that the gamma-ray emitting region roughly locate at 2*104 Rs, or ~ 10 RBLR(RBLR is the size of broad line region), which suggest that the most of the jet energy may dissipated at outside of BLR and roughly within the torus. The possible jet physics in nearby galaxies (e.g., M 87) will also be discussed.

Numerical simulations of intermittent radio jets

Yates, Patrick

Feedback from Active Galactic Nuclei on the host environment is required to maintain the delicate heating/cooling balance in massive galaxies over the latter half of the Hubble time. The process usually invoked is kinetic feedback from radio jets, which do work on their host hot atmospheres through supersonic outflows, shocks and gas uplifting._x000D_ I have carried out numerical hydrodynamical simulations of radio jets from active galactic nuclei in order to investigate the effect of different environments and intermittency of energy injection on the resulting dynamics, energetics, and observable properties of jet-inflated lobes._x000D_ Key features of these simulations include the pressure collimation of initially conical jets, and the inclusion of both active and passive jet evolution phases._x000D_ These simulations show that the environment into which a radio jet is propagating plays a large role in the resulting morphology and continuum surface brightness distribution of the radio source._x000D_ Additionally, feedback efficiency is found to be strongly dependent on the environment.

NGC4869 in Coma cluster: Its collimated radio jet and the role of Kelvin-Helmholtz instabilities

Lal, Dharam

The GMRT upgrade, an SKA pathfinder instrument is almost complete and has begun operations. The upgraded facility will complement several other observatories as essential tool for discovery in several areas of astrophysics. Here, we present radio and X-ray imaging of the Coma cluster, an important 'laboratory' to study the role of cluster environment on the properties of radio sources and demonstrate the importance of multi-wavelength imaging. We would also present a case study, using upgraded GMRT and Chandra, NGC4869 in Coma cluster - we report flaring of a straight, collimated jet at approximately the position where it crosses the surface brightness edge in the hot gas - with an aim to investigate the radio jet collimation on kpc-scales.

Radio/X-ray monitoring of the broad-line radio galaxy 3C 382

Ursini, Francesco

We present a unique radio/X-ray monitoring programme on the broad-line radio galaxy 3C 382, carried out in 2016 (Ursini et al., submitted). The campaign consisted of five joint XMM-Newton/NuSTAR observations, 20 ks each and separated by 12 days, performed simultaneously with VLBA. The high-energy (UV to hard X-rays) data are consistent with a two-corona scenario, in which the UV emission and soft X-ray excess below 1-2 keV are produced via thermal Comptonization in a warm (kT≈0.6 keV), optically thick (τ≈20) corona consistent with being a slab fully covering a nearly passive accretion disc, while the hard X-ray emission is due to a hot corona intercepting ~10% of the soft emission. These results are remarkably similar to those generally found in radio-quiet Seyferts (Petrucci et al. 2017), thus suggesting a similar inner flow structure. We also discuss the radio properties as seen with VLBA and their relation with the high-energy emission.

Wind production in active galactic nuclei

Bu, Defu

Observations of both Low-luminosity AGNs (LLAGNs) and Quasars show that wind is present. The accretion model for LLAGNs is hot accretion flow. I will talk about theory and numerical simulations of wind generation of hot accretion flow. In hot accretion flow, wind can be either magnetically or thermally driven. In the region inside the Bondi radius, wind can be driven by the combination of magnetic pressure gradient, gas pressure gradient and centrifugal forces. In the region around and outside Bondi radius, the flow is irradiated and heated by the central X-ray photons and wind can be thermally driven. I will also talk about theory and simulations of wind generated from Quasars. The accretion model for Quasar is standard thin disk. Wind can be either radiation pressure or magnetic driven in standard thin disk. The possible application of wind in AGN feedback study is also discussed.

Soft gamma-ray radio galaxies: a high-energy view of jetted AGNs

Ursini, Francesco

We discuss results of a multiwavelength study of a sample of ~70 radio galaxies, selected in the soft gamma-ray band from INTEGRAL and Swift/BAT catalogues (Bassani et al. 2016), focusing on the X-ray view. This ongoing study is aimed at characterizing for the first time the broad-band emission of a statistically significant sample of radio galaxies, thus constraining the accretion/ejection mechanisms at play in AGNs. The sample contains a significantly larger fraction of giant radio galaxies (linear size > 0.7 Mpc) than typically found in radio surveys; a talk focused on the properties of these peculiar objects is also proposed at this meeting (Bruni et al.). Concerning the X-ray absorption properties of the whole sample (Panessa et al. 2016), an intriguing result is the lack of heavily absorbed (Compton-thick) sources, which could hint for a discrepancy between the average absorption properties of radio-loud and radio-quiet AGNs (Ursini et al. 2018). We also study the relation between X-ray absorption and 21 cm HI absorption, finding a higher probability of 21 cm detection among X-ray absorbed sources. This might in turn suggest that at least part of the X-ray obscuration is due to atomic hydrogen seen at radio frequencies, and that could reside at distances larger than the classical pc-scale torus.

Growth of massive black holes in dusty clouds: impacts of relative velocity between dust and gas

Ishiki, Shohei

Recent observations have suggested the existence of a large amount of dust around supermassive black holes (SMBHs) in the early universe (e.g. Maiolino et al. 2004). In dusty clouds, the growth of black holes can be significantly regulated due to strong radiation force on dust grains. Yajima et al. (2017) recently showed that the accretion on to intermediate-mass black holes (IMBHs) in dusty clouds are significantly suppressed compared with dustless clouds because of the strong radiation force on dust grains. They, however, assumed that the dust and gas are completely coupled. This assumption might be invalid in the vicinity of black holes. The relative velocity between dust and gas is likely to have impacts on the accretion rate._x000D_ We here investigate the impacts of the relative motions of dust and gas on the accretion rate onto IMBHs with the mass of 105 Msun by using one-dimensional radiation hydrodynamic simulations in clouds with initial gas densities of nH = 10 and 100 cm-3. To investigate the effect of grain size on the gas accretion, we introduce two additional fluid components which describe large (0.1 μm) and small (0.01 μm) dust grains in the simulations as we did in Ishiki et al. (2018)._x000D_ We show that the accretion rate is reduced due to the radiation force. We show that the dust-to-gas mass ratio significantly changes in HII regions because of the relative motions of dust and gas. The decoupling of dust from gas alleviates the suppression of black hole growth compared with the complete coupling case. This effect may allow moderate growth of black holes even in dusty clouds.

Physical and chemical properties of narrow-line regions in z~3 radio galaxies through multi-line analysis

Terao, Koki

Physical and chemical properties of the interstellar medium (ISM) in galaxies and their redshift evolution are important to understand the formation and evolution of galaxies. The ISM properties of massive galaxies at z > 2 are particularly interesting, because the evolution of massive galaxies had been already completed at such high redshift. However, normal massive-galaxies at z > 2 are too faint to be examined in detail. On the other hand, emission-line spectra of narrow-line regions (NLRs) in active galactic nuclei (AGNs) offer an alternative approach to investigate the ISM properties of high-z massive galaxies. _x000D_ In this work, we use the rest-UV spectra of three radio galaxies at z ~ 3 observed with VLT/FORS2 for trying to measure the flux of several emission lines including relatively faint ones. As a result, we detect some faint emission lines such as the NIV]λ1486, OIII]λ1665, and [NeIV]λ2424. In addition, we collect the UV-emission line fluxes of seven z ~ 3 radio galaxies from the literature. We diagnose the physical and chemical properties of the ISM for each object through the comparison between the measured emission-line fluxes and detailed photoionization models with Cloudy. We confirm that the metallicity of NLRs in AGNs at z ~ 3 is higher than the solar metallicity, without assuming the gas density and ionization parameter thanks to the newly detected faint emission lines. This result suggests that high-redshift radio galaxies have matured chemically at z ~ 3. More interestingly, the inferred gas density and ionization parameter are systematically higher than those seen in NLRs of low-z SDSS AGNs. This result implies that ISM properties of AGN host galaxies show redshift evolutions.

How do X-shaped radio galaxies form?

Sebastian, Biny

We present our low-frequency radio study of an extended sample of X-shaped sources using the Giant Metrewave radio telescope (GMRT) done with a primary aim to distinguish between various models for the formation of X-shaped radio sources. This study concentrates on the study of spectral properties of the active lobes versus the off-axis emission observed in X-shaped radio galaxies. The combined sample consists of 26 X-shaped radio galaxies which were observed using the GMRT at two frequencies (610 and 240 MHz). We find that the general class of X-shaped radio galaxies tend to show comparable spectral indices in both the active lobes and the wings and the steepening of spectrum that is usually seen in a general FR II radio galaxy population is observed rarely. We speculate that such a behaviour is due to the re-acceleration of the plasma due to the turbulence induced by a merger of galaxies. We have also tried to explore the possibility that several different mechanisms play a role in the formation of these objects rather than a single unified model for the entire class of X-shaped radio sources. We will also discuss the role of twin AGN models in the formation of such objects.

Particle Acceleration, Turbulence and Multi-Wavelength Radiation in Blazar Jets

Baring, Matthew

Jets in blazars are an excellent forum for studying acceleration at relativistic MHD shocks, since this process is likely to spawn the highly-variable emission seen across the electromagnetic spectrum from radio to gamma-rays. Our recent work on combining multi-wavelength leptonic emission models with complete simulated distributions from shock acceleration theory has resulted in new insights into plasma conditions in blazar jets, likely to apply to radio galaxies as well. This has demonstrated the ability to infer the plasma density, and suggested the interpretation that turbulence levels decline with remoteness from jet shocks, with a significant role for non-gyroresonant diffusion. In this paper, we extend this program to a two-zone time-evolving construction, modeling together both extended, enhanced emission states from larger radiative regions, and prompt flare events in select Fermi-LAT and TeV blazars. A prime goal is to ascertain whether such flares are truly associated with prompt shock acceleration activity in relatively confined regions. The results illustrate how parametric degeneracies in shock acceleration conditions can lead to refined determinations of the plasma density and particle diffusion character in blazar jets.

Optical Study of Bright FERMI/LAT Blazars

Nikolashvili, Mariam

To study optical variability of extragalactic sources during last twenty years we are conducting in Abastumani Observatory a long-term monitoring campaign using dedicated telescopes, which allowed collecting 300000 CCD frames during ~3100 nights. This extensive monitoring campaign a few dozen blazars first five years was carried out in BVRI bands and later on from 2002 mainly in R band using the 70-cm meniscus (f/3, SBIG ST6 and Apogee Ap6E) and 125-cm Ritchey-Chretien (f/13, Apogee Ap6E) telescopes. Most dense coverage of selected LAT brightest sources has been undertaken after lunch of FERMI satellite in 2008. The frames have been reduced using Daophot II and homogenous sample of light curves have been constructed. Most sources show wide range of variability (long-term, IDV and micro-variability). We present optical light curves of these most well sampled sources.

Why are only a small fraction of quasars radio-loud?

Cao, Xinwu

It is still a mystery why only a small fraction of active galactic nuclei (AGNs) contain relativistic jets. A strong magnetic field is a necessary ingredient for jet formation, however, the advection of the external field in a geometrically thin disk is inefficient. Gas with a small angular velocity may fall from the Bondi radius {R}{{B}} nearly freely to the circularization radius {R}{{c}}, and a thin accretion disk is formed within {R}{{c}}. We suggest that the external magnetic field is substantially enhanced in this region, and the magnetic field at {R}{{c}} can be sufficiently strong to drive outflows from the disk if the angular velocity of the gas is low at {R}{{B}}. The magnetic field is efficiently dragged in the disk, because most angular momentum of the disk is removed by the outflows that lead to a significantly high radial velocity. The strong magnetic field formed in this way may accelerate jets in the region near the black hole, either by the Blandford-Payne or/and Blandford-Znajek mechanisms. We suggest that the radio dichotomy of AGNs predominantly originates from the angular velocity of the circumnuclear gas. An AGN will appear as a radio-loud (RL) one if the angular velocity of the circumnuclear gas is lower than a critical value at the Bondi radius, otherwise, it will appear as a radio-quiet (RQ) AGN. This is supported by the observations that RL nuclei are invariably hosted by core galaxies. Our model suggests that the mass growth of the black holes in RL quasars is much faster than that in RQ quasars with the same luminosity, which is consistent with the fact that the massive black holes in RL quasars are systematically a few times heavier than those in their RQ counterparts.

Molecular gas reservoirs in Low Luminosity Radio Galaxies at z~0.4-2.6 in dense Mpc-scale environment

Castignani, Gianluca

At variance with powerful radio galaxies (RGs) Low Luminosity Radio Galaxies (LLRGs) represent the bulk of the RG population and are often associated with the brightest cluster galaxies (BCGs). LLRGs are in fact a precious tool to discover distant (proto-)clusters and can be effectively used to probe the effect of dense Mpc-scale environment on molecular gas, even close to the AGN. Molecular gas has never been searched for in the host galaxies of distant LLRGs, which show lower level of AGN activity and therefore resemble better normal galaxies than powerful RGs. We search for CO in a sample of five distant LLRGs, at z=0.4, 0.6, 0.9, 0.9, and 2.6, within the SDSS (at z<=0.6) and COSMOS (at z>=0.9) surveys. The LLRGs are detected at 24μm by Spitzer/WISE, which suggests significant ongoing star formation activity. Evidence of dense Mpc-scale environment is found for all five LLRGs by looking for overdensities of photometric redshifts around them. The two LLRGs at z=0.9 from COSMOS are also hosted in rich X-ray groups. By exploiting IRAM-30m telescope observations and assuming a Galactic CO-to-H2 conversion we set SNR=3 upper limits M(H2)<2e+09 Msun to the total molecular gas content associated with each of the four z<=0.9 LLRGs. Tentative SNR=2.3 detection of CO(7-6) is found for the remaining z=2.6 LLRG, corresponding to M(H2)=2e+10Msun. If the detection is confirmed at higher SNR with better sensitivity observations (e.g., NOEMA, ALMA) such z=2.6 LLRG would be the most distant proto-BCG ever detected in CO. Our observations suggest that highly star forming BCGs are rare. Our LLRGs are optimal targets for NOEMA/ALMA to distinguish between gas processing mechanisms occurring in distant BCGs such as gas stripping, cooling flows, or major mergers.

Uncovering the unknown population of disk galaxies hosting large-scale radio emission

Duchesne, Stefan

It is uncommon to find dusty disk galaxies hosting powerful AGN, and so large-scale radio emission (> 100 kpc) is not typically seen from such galaxies. However, in rare circumstances this is observed and the alignment is not likely by chance. The number of disk galaxies hosting large-scale radio emission is steadily growing, with new detections resulting from dedicated searches or found serendipitously. Here we present the serendipitous detection of two such sources, and discuss their properties within the context of other disk galaxies hosting large-scale radio emission. We also present new Australia Telescope Compact Array and Murchison Widefield Array data of the emission surrounding NGC 1534. The number of sources currently detected is now sufficient to suggest the presence of an as yet unstudied population of radio galaxies. This suggests that further dedicated searches utilising various current and upcoming radio surveys in combination with optical surveys will shed light on the statistics and optical and radio properties of this largely unstudied class of objects.

Infrared properties of optically-faint radio galaxies/quasars discovered by Subaru/HSC and FIRST

Toba, Yoshiki

We present physical properties of optically-faint (i_AB > 21) radio galaxies/quasars newly discovered by Subaru Hyper-Supreme Cam (HSC) and VLA Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey. By cross-matching 3579 HSC-FIRST galaxies/quasars (Yamashita et al. 2018) with Wide-field Infrared Survey Explorer (WISE) data, we selected 2354 radio galaxies/quasars with infrared (IR) data. We investigated their mid-IR properties and compared those with optically-bright (i_AB < 21) FIRST galaxies/quasars detected by the Sloan Digital Sky Survey (SDSS). We found that (i) 3.4 micron - 4.6 micron color and 4.6 micron - 12 micron color of HSC-FIRST galaxies/quasars are redder than those of SDSS-FIRST galaxies/quasars given a redshift, and (ii) the dust extinction, E(B-V) of HSC-FIRST galaxies/quasars that is derived from the SED fitting of optical and near-IR data, are systematically larger than those of SDSS-FIRST galaxies/quasars. These results suggest that HSC-FIRST galaxies/quasars are more dusty and IR luminous objects heated by strong SF/AGN radiation. We also investigated the physical properties of HSC-FIRST galaxies/quasars such as stellar mass and star formation rate (SFR) based on the SED fitting to the multi-wavelength dataset of u-bad (KiDS DR3), near-IR (VIKING DR3), mid-IR (ALLWISE), and far-IR (Herschel PSC).

Optically-faint radio galaxies found by Subaru HSC-SSP and FIRST catalogs

Yamashita, Takuji

We will present statistical optical and radio properties of optically-faint radio galaxies found by an on-going project, a Wide and Deep Exploration of Radio Galaxies with the Subaru HSC (WERGS). Radio galaxies are bright sources in radio wavelength, involving powerful radio-jets, which could give a so-called feedback effect on host galaxies. Because the host galaxies are thought to be typically massive, radio galaxies are important for understanding the evolution of massive galaxies and also the nuclear supermassive black hole. However, while there exist wide and deep radio surveys, compatible wide optical surveys have been not enough deep. The SDSS has identified optical counterparts of only ~30 % among the FIRST radio sources due to the faintness in optical (i < 21 mag).In order to overcome this situation, we carried out the search for optically-faint radio galaxies by combing both the Subaru HSC-SSP catalog and the FRIST catalog (Yamashita et al. 2018 in prep.). The HSC-SSP compiles faint sources down to i = 27 mag. As a result, we identified ~3,600 radio galaxies in the field of 156 square degree. The number of the matches is equivalent to ~50 % of FIRST sources in the search field. In particular, we found a large number of radio galaxies with large radio-loudness (log R > 4) at an optically-faint regime (i > 21 mag). These optically-faint radio galaxies are mostly located at photometric redshifts z_ph > 1. The results may infer high-z optically-faint radio galaxies have low accretion rate or obscured nuclei. The optical color of optically-bright HSC-FIRST radio galaxies at z_ph ~< 1is consistent with that of passive galaxies. Meanwhile, the optically-faint radio galaxies at z_ph > 1 show blue color of g-z < 2, which is not consistent with that of passive galaxies but can be explained by predominant young stellar populations. The optically-faint radio galaxy sample found by Subaru HSC-SSP and FIRST may include “evolving” radio galaxies that are star-forming.

Long-term study of TeV blazars

Kurtanidze, Omar

About fifty (Mrk 421, Mrk 501, 1ES 1959+650 and others) northern TeV extragalactic sources have been discovered during last twenty five years. Most of them (2/3) we are monitoring in Abastumani Observatory during 20 years using 125-cm and dedicated 70-cm meniscus telescopes. All observations (over 3100 nights) have been conducted with Apogee Ap6E and SBIG ST-6 CCD cameras in BVRI bands. The frames have been reduced using Daophot II and homogenous lightcurves have been constructed. The amplitudes of long-term variability are within 0.3-1.5 magnitudes. Few sources show Intra-day variability within 0.05-0.15 magnitudes, while intra-night/micro-variability is below 0.05 magnitudes. The extensive multi-wavelength campaigns with Whipple, VERITAS, HESS and MAGIC have also been conducted.

Use of Medium Size Telescopes and CCD Cameras to study blazars

Kurtanidze, Omar

The first report on micro-variability in AGNs was announced in the beginning of 60-ies, when a few sources were studied with a single-channel photoelectric photometer and biggest Palomar telescopes. Nevertheless, these variations were received with skepticism due to the instrumental instabilities and the inherent non repeatability of time-critical observations. Availability and utilization of CCD cameras breathed new life to small telescopes. During last decades, the variability time-scales from minutes to years have been studied for many blazars using commercial CCD cameras and small telescopes. A short review of blazar monitoring programs conducted during last 20 years in Abastumani Observatory and future prospects will be presented.

Impact of intergalactic environment on the radio-morphologies of Giant sources.

Roy, Rupak

Radio galaxies are the known most giant radio sources in the visible universe. Although, all of them have prominent jet like outflows, considerable differences among their jet activities as well as in their morphologies can be found in their radio-images. This eventually lead us to a wide classification scheme : FR-I, FR-II, GRG, DDRG, Wide-angle tail and S-shape sources. Jets are launched from the center, very near to the supermassive black hole (SMBH) of the host galaxy, so certainly jet activities are governed by the central SMBH. However at sufficient distance from the host, in the intergalactic medium the flow of jet material is also influenced by the ram-pressure of the environment. In this presentation we will discuss the Impact of  intergalactic environment on the radio-morphologies of Giant sources on the basis of local galaxy population around them. For this purpose we have used the data from the radio surveys conducted by VLA and the optical data from SDSS survey.

Modelling the jet kinematics of OJ287: paradigm for other blazars?

Zajacek, Michal

OJ287 belongs to one of the best candidates among active galactic nuclei to host the binary supermassive black hole at very close separation. Based on a recent analysis of 120 VLBA (Very Long Baseline Array) observations at 15 GHz by Britzen et al., we set up a basic kinematical model to explain the motion of jet components. The model involves the jet precession, on top of which we find an indication of additional nutation-like motion for the first time. The ratio of the precession and nutation periods is about 20. The precessing motion is quite natural in the supermassive black hole binary system, due to the torques exerted by the companion black hole on the accretion disc around the primary. The other explanation is provided by the disc misalignment with respect to the spin of a single black hole. The jet precession then occurs due to the Lense-Thirring effect. Both scenarios indicate a rich merger history of OJ287, which may be a general characteristic of blazars. This model contribution is complementary to the observational contribution by Britzen et al.

PAGaN: Revealing the Nature of Blazar Radio Cores through Multi-Frequency Polarization Observations with the Korean VLBI Network

Trippe, Sascha

We study the linear polarization of the radio cores of eight blazars simultaneously at 22, 43, and 86 GHz with observations obtained by the Korean VLBI Network (KVN) in three epochs between late 2016 and early 2017 in the frame of the Plasma-physics of Active Galactic Nuclei (PAGaN) project. We investigate the Faraday rotation measure (RM) of the cores; the RM is expected to increase with observing frequency if core positions depend on frequency due to synchrotron self-absorption. We find a systematic increase of RMs at higher observing frequencies in our targets. The RM–? relations follow power-laws with indices distributed around 2, indicating conically expanding outflows serving as Faraday rotating media. Comparing our KVN data with contemporaneous optical polarization data from the Steward Observatory for a few sources, we find indication that the increase of RM with frequency saturates at frequencies of a few hundreds GHz. We claim that blazar cores become fully transparent, with no more core-shift occurring, above that frequency. This implies that, at high frequencies, the radio core is a standing recollimation shock. The Faraday screens of our sources seem to be external to their jets; a sub-relativistic sheath surrounding a relativistic jet is a promising candidate for the location of the Faraday rotating medium. We detect sign changes in the observed RMs of CTA 102 on time scales of months, which might be related to new superluminal components emerging from its core undergoing acceleration/deceleration and/or bending. We see indication for quasars having higher core RMs than BL Lac objects, which could be due to denser inflows/outflows in quasars.

The nature of radio and optically variable radio sources

Abrahamyan, Hayk

We have cross-correlated NVSS and FIRST radio catalogues having radio flux measurements at the same 1.4 GHz frequency to benefit from repeated observations from both catalogues, which give more accurate positions and fluxes and more important, reveal large differences between the two measured fluxes, thus allowing to establish radio variability. 79,382 radio variables have been revealed, including 6301 with flux differences at 1.4 GHz larger than 15 mJy, 1917 with flux differences > 45 mJy and 260 with flux differences > 200 mJy. By using a special technique (Mickaelian & Sinamyan 2010, Mickaelian et al. 2011) we have revealed 2425 optically variable objects out of 6301 radio sources. We have divided 2425 radio sources with both high radio and optical variability into four categories. 1206 (19%) out of 6301 radio sources have activity types from available catalogues and 619 (25.5%) out of 2425 radio sources with at the same time radio and optical variability have activity types from available catalogues. In addition, 279 radio sources out of 2425 have high variability in optical range. We have established their activity types when available. We have studied the IR fluxes and colours for the 6301 variable radio sources. Colour-colour diagrams show that most of the “unknown” sources are galaxies. We also have retrieved the activity type for 110 (42%) out of 260 extremely high variable radio sources.

Extended parameter study of the self-similar relativistic MHD equations for black hole outflows

Ceccobello, Chiara

Jets are ubiquitous and reveal themselves at different scales and redshifts, showing an extreme diversity in energetics, shapes and emission, in objects such as X-ray binaries (XRBs) and active galactic nuclei (AGN), as well as young stellar objects (YSOs) and gamma-ray bursts (GRBs). Observations suggest that jets are an energetically important component, not only to the systems that host them, but also their larger surrounding environments, where they deposit a significant amount of energy that has been extracted from the accretion flow. Therefore, understanding the mechanisms responsible for the formation and emission of jets is a fundamental problem to be addressed. In this talk, I will present a new integration scheme to solve scale-invariant, relativistic and non-relativistic MHD equations describing collimated Blandford-Payne outflows.For the first time, jet solutions can be reconstructed from the disk mid-plane to downstream of the modified magnetosonic fast point, while smoothly crossing the three singular surfaces (modified slow/fast and Alfven surfaces).Relativistic solutions show a wide range of jet dynamics (jet Lorentz factor ~ 1-10) and geometric properties (i.e. shock height ~ 10^3 - 10^7 Rg), which is even more broadened by the inclusion of the non-relativistic solutions grid. Such diversity makes our model suitable for application to many different systems in which relativistic jets are launched.

ALMA observations a 1mm and the detection of Propynal


Past surveys at mm wavelengths from the prototypical starburst galaxies NGC 253 and M82 have shown chemical abundance of molecular species to vary significantly as a function of the evolutionary stage of each starburst nuclear region.   Multi-line ALMA studies of NGC 253 at 3mm and 0.85mm were published in 2015 and 2017 which reports the tentative detection of molecules previously undetected from single dish observations.We report a first part of ALMA observations using an array of 38 antennae in band 7 of the starburst galaxy NGC 253 at 1mm, we mapped at an angular resolution of 0.26 arcseconds toward the starburst galaxy NGC 253. Amongst other molecules, we did a tentative detection of Propynal and prebiotic molecules. We determined the flux density for each molecule with components and transitions; we studied the spatial distribution and present the corresponding integrated maps, also the position velocity maps. Flux is consistent with previous authors of the same source with ALMA. We compare our results with those from other sources and other frequencies as well as with the Galactic Center.

OJ287: Deciphering the “Rosetta stone of blazars”

Britzen, Silke

OJ287 is the best candidate Active Galactic Nucleus (AGN) for hosting a supermassive binary black hole (SMBBH) at very close separation. We present a re-analysis of 120 Very Long Baseline Array (VLBA) observations (at 15 GHz, MOJAVE survey) covering the time between Apr. 1995 and Apr. 2017. We find that the OJ287 radio jet is precessing on a timescale of ~ 22 yr. In addition, our data are consistent with a jet-axis rotation on a yearly timescale. We model the precession (24±2 yr) and combined motion of jet precession and jet-axis rotation.  The jet dynamics and flux-density light curves can be understood in terms of geometrical effects. Disturbances of an accretion disk caused by a plunging black hole do not seem necessary to explain the observed variability. Although the SMBBH model does not seem necessary to explain the observed variability, a SMBBH or Lense-Thirring precession (disk around single black hole) seem to be required to explain the timescale of the precessing motion.

The cold gas reservoir feeding a distant interacting young radio galaxy

Allison, James

While some radio galaxies show stong emission lines in the optical, characteristic of an active galactic nucleus (AGN), others do not. We have substantial circumstantial evidence that this dichotomy is the result of the mode in which gas is accreted onto the nucleus. However, the exact mechanisms by which high and low excitation radio galaxies are nourished can only be determined through direct observation of the gas. A powerful method for measuring the kinematics of gas deep into the centres of radio-loud AGN is through detection of the HI 21-cm hyperfine and CO rotational lines in absorption. The Australian Square Kilometre Array Pathfinder (ASKAP), in its commissioning and early science phase, has been very successful in detecting HI absorption in powerful radio galaxies at intermediate cosmological redshifts. In followup observations using ALMA we have detected 12CO(2-1) absorption in PKSB1740-517, a young luminous radio galaxy at z=0.44 that has likely undergone a recent interaction with its companion galaxies. I will discuss the results of this work, including how we can disentangle the line-of-sight ambiguities from absorption and what we learn about the system by combining the ASKAP, ALMA and multiwavelength ancillary data. 

Zooming into the AGN properties with Space VLBI

Gurvits, Leonid

Investigation of the physics of the AGN phenomenon requires, among other methods, ultra-high angular resolution, offered in radio domain by Very Long Baseline Interferometry (VLBI). The extension of VLBI into space with baselines exceeding the Earth diameter offers the highest achievable today angular resolution reaching single-digit microarcseconds. The Space VLBI mission RadioAstron which operates in orbit since 2011 completed the observational part of its AGN Survey project in 2017. The Survey sample includes 247 sources observed at 5 and partially 1.6 GHz over the total of 2000 hours. The observations were conducted in the non-imaging mode at the baselines ranging from several to 27 Earth diameters; the latter, at 6 cm wavelength provides the angular resolution of ~30 uas. Importantly, since the ability of an interferometer to tackle the highest brightness temperatures requires the longest physical length of a baseline, the RadioAstron offers a unique opportunity to measure directly the brightness temperatures exceeding the value of 1011.5 K, dictated by the Inverse Compton “catastrophe”. Indeed, such the ultra-high brightness has bee detected in several AGN. The presentation will discuss these results and their possible implications for the physics of the radio emission mechanism in AGN. Another result of the RadioAstron AGN Survey project is a pioneering detection of refractive scattering of radio emission in the interstellar medium. This is a long predicated phenomenon with manifestations reachable only with baselines exceeding the Earth diameter. We will discuss how the presence of refractive scintillations might impact estimates of physical parameters of AGN.The RadioAstron AGN Survey data are being analysed in concurrence with several ground-based observing programmes in radio and other domains of the electromagnetic spectrum. The presentation will review the current status of the overall RadioAstron AGN Survey data analysis and its perspectives

Restarting activity in the nucleus of PBC J2333.9-2343

Hernandez-Garcia, Lorena

Under unification schemes, active galactic nuclei (AGN) can be explained by orientation effects. However, some sources show properties at different frequencies that led to incongruent classifications and cannot be explained by such unification scheme. This is the case of PBC J2333.9-2343; its optical spectrum is of a type 2 AGN but its X-ray spectrum does not show signs of absorption, and in the radio it has many features typical of a blazar but it is a giant radio galaxy. Using multiwavelength simultaneous data from XMM-Newton, San Pedro Mártir telescope and VLBA, we find that these classifications cannot be attributed to variability. We propose that PBC J2333.2343 is a blazar that has undergone a restarting activity episode in its nucleus. Interestingly, it has changed from being a radio galaxy to become a blazar, showing an exceptional change in the direction of the jet that, by chance, occurred in the plane of the sky. It also shows a change in the broad line region (BLR) clouds and increasing variability at all observed wavelengths and we have detected an outflow in its optical spectra.

Double irony in XXL North: A tale of two radio galaxies in a supercluster at z = 0.14

Horellou, Cathy

XXL is a multiwavelength extragalactic survey that is particularly well suited to study the interplay between active galactic nuclei (AGN), galaxies and clusters of galaxies, and the large-scale structure. Our aim is to use XXL to shed light on radio galaxies and their environment by investigating the two most spectacular radio galaxies in XXL North.We identified the two radio galaxies in a visual examination of the mosaic of XXL North obtained with the Giant Meterwave Radio Telescope (GMRT) at 610 MHz. Counterparts were searched for in other bands, from X-ray to the infrared, to characterize the host galaxies and their environment. Spectroscopic redshifts from the GAMA database were used to identify clusters/groups of galaxies and estimate their masses.Both radio galaxies are of FR I type and hosted by early-type, passive galaxies at a redshift of 0.14. The first radio source, named the Exemplar, has a physical extent of about 400 kpc; it is located in the cluster XLSSC112 that has  a temperature of about 2 keV and resides in an XXL supercluster with eight known cluster members. The second radio galaxy, that we named the Double Irony because of its peculiar shape (two reversed question marks), has a physical size of about 900 kpc. The position of its core coincides with that of a cataloged point-like X-ray source, but no extended X-ray emission from a surrounding galaxy cluster was detected. However, from the optical data we determined that the host of the Double Irony is the brightest galaxy in a group that is younger, less virialized, and a few times less massive than the Exemplar's cluster. A Friends-of-Friends analysis showed that the Double Irony's group is a member of the same supercluster as the Exemplar.This work shows that radio galaxies can be used to identify galaxy clusters/groups that are missed in X-ray surveys.

A detailed view of the tailed radio galaxy 3C 31 with LOFAR

Heesen, Volker

We present a deep, low-frequency radio continuum study of the nearby Fanaroff–Riley class I (FR I) radio galaxy 3C 31 using a combination of Low-Frequency Array (LOFAR; 30–85 and 115–178 MHz), Very Large Array (VLA; 290–420 MHz), Westerbork Synthesis Radio Telescope (WSRT; 609 MHz) and Giant Metre Radio Telescope (GMRT; 615 MHz) observations. Our new LOFAR 145-MHz map shows that 3C 31 has a largest physical size of 1.1 Mpc in projection, which means 3C 31 now falls in the class of giant radio galaxies. We model the radio continuum intensities with advective cosmic ray transport, evolving the cosmic ray electron population and magnetic field strength in the tails as functions of distance to the nucleus. For this we use models from SPINNAKER, the SPectral INdex Numerical Analysis of K(c)osmic-ray Electron Radio-emission, which is a computer program that calculates non-thermal radio spectral indices for 1D cosmic ray transport of pure advection and diffusion. We find that if there is no in situ particle acceleration in the tails, then decelerating flows are required that depend on radius r as v ~ r^beta (beta = -1). This then compensates for the strong adiabatic losses due to the lateral expansion of the tails. We are able to find self-consistent solutions in agreement with the entrainment model of Croston & Hardcastle, where the magnetic field provides ~1/3 of the pressure needed for equilibrium with the surrounding intracluster medium. We obtain an advective time-scale of ~190 Myr, which, if equated to the source age, would require an average expansion Mach number M ~ 5 over the source lifetime. Dynamical arguments suggest that instead either the outer tail material does not represent the oldest jet plasma or else the particle ages are underestimated due to the effects of particle acceleration on large scales. Hence, LOFAR reveals entirely unknown parts in one of the best-studied radio galaxies that are invisible at GHz-frequencies due to spectral ageing.

Probing the Dynamics & Energetics of Radio-loud AGN

Mahatma, Vijay

Radio jets are the large-scale and extragalactic footprints of accretion onto supermassive black holes, and are suggested to be the key ingredient controlling the galaxy mass function. Of particular importance is their jet power - the time-averaged energetic feedback into their environment. To determine a jet power, an accurate estimate of the age of the radio source is required, which is known to give discrepant results based on the method of calculation. Here, we attempt to resolve the spectral age/dynamical age discrepancy using high resolution radio and X-ray observations of two powerful radio galaxies, and consequently determine their source energetics. I also present some recent observations of the rare classes of remnant and restarting radio galaxies, which are crucial to inferring the global duty cycle of radio galaxies.

Morphological study of a large sample of extragalactic radio sources for revelation of radio jets

Mickaelian, Areg

With an improved cross-correlation technique, we have matched two largest radio catalogs at 1.4 GHz (21 cm), NVSS and FIRST to improve positions and photometry, to reveal radio variability and check with optical variability, to study the radio structure and optical morphology of sources, to classify radio sources into FRI and FRII types, and to reveal jets and additional features. NVSS (Condon et al. 1998) contains 1,773,484 sources and FIRST (Helfand et al. 2015) contains 946,432 sources and have better positional and photometric accuracy (5 arcsec and 1 mJy, respectively). As a preliminary result, we obtained 556,282 common sources. 6301 of them show obvious signs of variability having > 50 mJy differences between fluxes in NVSS and FIRST. For these sources we have made multiwavelength (MW) investigations in all wavelength ranges aimed at finding relations between the radiation fluxes in different bands for different types of sources (blazars, QSOs, other AGN, and starbursts). Another possibility that appeared after having cross-correlated NVSS/FIRST sources, is the study of radio morphology. Given that FIRST resolution is higher, very often we have 2-4 FIRST associations within 30 arcsec corresponding to 1 NVSS source. In such cases the central source is considered as the core, and 2 farther bright sources are considered as radio lobes. Depending on the flux ratio of the central source and the lobes, we have preliminarily classified sources to FRI and FRII. On the other hand, the 4th component, when available, may be regarded as a jet, and very often it appears not far from the core. We match these results with radio contours to verify candidate jets, as well as we check these sources for radio variability. We identify NVSS/FIRST sources having 4 FIRST components and radio variability, a highly reliable sample for revelation of radio jets.

The cosmic radio dipole

Schwarz, Dominik

The most pronounced anisotropy of the cosmic microwave background (CMB) is a dipole. It is believed to be caused by the proper motion of the Solar system, but this is a hypothesis that must be tested. Tests based on the Planck data allow for a 40% non-kinetic contribution to the CMB dipole. Large radio continuum surveys can test this proper motion hypothesis and probe the largest observable cosmic structures. We present estimates of the cosmic radio dipole at several frequency bands, based on catalogues from TGSS, WENSS, SUMSS and NVSS. The resulting radio dipole directions are consistent with the CMB dipole. However, the inferred radio dipole amplitude exceeds the expectation based on the proper motion hypothesis significantly and seems to depend on frequency. We discuss possible issues and explanations.

Is there a maximum mass for supermassive black holes?

Ichikawa, Kohei

Recent quasar surveys have revealed that supermassive black holes (SMBHs) rarely exceed a mass of MBH ~ a few * 1010 Msunduring the entire cosmic history. It has been argued that quenching of the BH growth is caused by a transition of a nuclear accretion disk into an advection-dominated accretion flow, with which strong outflows and/or jets are likely to be associated. We investigate the relationship between the maximum mass of SMBHs and the radio-loudness of quasars with a well-defined sample of ~ 105 quasars at a redshift range of 0 < z < 2, obtained from the Sloan Digital Sky Surveys DR7 catalog. We find that the number fraction of the radio-loud (RL) quasars increases above a threshold of MBH ? 2 x 109 Msun, independent of their redshifts. Moreover, the number fraction of RL quasars with lower Eddington ratios (out of all RL quasars), indicating lower accretion rates, increases above the critical BH mass. These observational trends can be natural consequences of the proposed scenario of suppressing BH growth around the apparent maximum mass of ~1010 Msun. The ongoing VLA Sky Survey in radio will allow us to estimate of the exact number fraction of RL quasars more precisely, which gives further insight into the quenching processes for BH growth.

High-resolution radio imaging of two luminous quasars beyond redshift 4.5

Titov, Oleg

Radio-loud active galactic nuclei in the early Universe are rare. The quasars J0906+6930 at redshift z=5.47 and J2102+6015 at z=4.57 stand out from the known sample with their compact emission on milliarcsecond (mas) angular scale with high (0.1-Jy level) flux densities measured at GHz radio frequencies. This makes them ideal targets for very long baseline interferometry (VLBI) observations.We present sensitive high-resolution VLBI images of J0906+6930 and J2102+6015 at two observing frequencies, 2.3 and 8.6 GHz. The data were taken in an astrometric observing programme involving a global 5-element radio telescope array. We combined the data from 8 di erent epochs from February 2017 to April 2018. For one of the highest-redshift blazars known, J0906+6930, we confirm that this source has a sharply bent helical inner jet structurewithin about 3 mas from the core. The quasar J2102+6015 shows an elongated radio structure in the east–west direction within the innermost ~2 mas that can be described with a symmetric 3-component brightness distribution model at 8.6 GHz. Analysis of individual positions of J2102+6015 collected since 2012 reveals a tiny proper motion of 12.8 +/- 2.3 muas/y to the eastern direction confirming the conclusion obtained with a limited imaging data. Our results demonstrate that VLBI observing programmes conducted primarily with astrometric or geodetic goals can be utilized for astrophysical purposes as well.

X-ray variations of one changing-look quasar

Ai, Yanli

We report the changing-look quasar which went through a dramatic outburst, during which its X-ray flux increased by an order of magnitude after an increase of its optical/mid-infrared continuum flux. With the appearance of broad optical emission lines, this changing-look quasar provide us with important insights about the quasar physics. 

Radio-Loud Unification: Multiple Radio Frequency Study

Vaddi, Sravani

AGN unification scheme attempts to unite different classes of AGN based on the idea that intrinsically similar objects appear different when viewed at different angles with respect to the line of sight.  In AGNs with powerful radio emission known as radio-loud (RL) AGN, the unification scheme claims that radio galaxies are parent populations of RL quasars (RLQ) and BL Lac objects.  AGN unification scheme has gained considerable success, however, there are still unsolved issues.  We address these issues by studying a sample of RLQ and FR II radio galaxies using 1.4 and 5 GHz observations at matched resolution with the Very Large Array (VLA).  We find that radio-loud unification largely holds but environmental factors also play an important role and cannot be ignored.

Extremely Rapid X-Ray Flares of TeV Blazars in the RXTE Era

Xue, Yongquan

Rapid flares from blazars in very high-energy (VHE) gamma-rays challenge the common understanding of jets of active galactic nuclei (AGNs). The same population of ultra-relativistic electrons is often thought to be responsible for both X-ray and VHE emission. We thus systematically searched for X-ray flares at sub-hour timescales of TeV blazars in the entire Rossi X-ray Timing Explorer archival database. We found rapid flares from PKS 2005-489 and S5 0716+714, and a candidate rapid flare from 1ES 1101-232. In particular, the characteristic rise timescale of PKS 2005-489 is less than half a minute, which, to our knowledge, is the shortest among known AGN flares at any wavelengths. The timescales of these rapid flares indicate that the size of the central supermassive black hole is not a hard lower limit on the physical size of the emission region of the flare. PKS 2005-489 shows possible hard lags in its flare, which could be attributed to particle acceleration (injection); its flaring component has the hardest spectrum when it first appears. For all flares, the flaring components show similar hard spectra with Gamma = 1.7-1.9, and we estimate the magnetic field strength B~0.1-1.0 G by assuming synchrotron cooling. These flares could be caused by inhomogeneity of the jets. Models that can only produce rapid gamma-ray flares but little synchrotron activity are less favorable.

BCGs radio analysis from a EGMRT and CLASH sample of galaxy clusters

Terni de' Gregory, Beatrice

Among the radio galaxy hosts, the Brightest Cluster Galaxies (BCGs) witness special conditions, being large objects at the center of a deep potential well.To properly evaluate the contributions of Star Formation (see Fogarty K. 2015 and Donahue M. 2015) and of their active nucleus to the radio emission, we are studying a sample of eleven BCGs selected mainly from the radio EGMRT (Kale R. 2015) and the optical CLASH (Postman M. 2012) surveys.In this talk I will present important results from this study pointing out the radio properties of these galaxies in relation with the dynamical status of their environment. Both Star Formation and AGN activities are important components of feedback mechanisms proposed to reconcile the discrepancy between the predicted and the observed cooling rate in cool core clusters.

FR-type radio sources in COSMOS: relation to large-scale environment

Vardoulaki, Eleni

The radio sources associated with active galactic nuclei (AGN) can exhibit a variety of radio structures, from simple to more complex, giving rise to a variety of classification schemes. Here we present an analysis on the radio structure of radio AGN from the VLA-COSMOS 3-GHz Large Project in relation to the environment their hosts lie within. We classify these as FRI (jet-like) and FRII (lobe-like) radio AGN based on the FR-type classification scheme, and compare them to a sample of jet-less radio AGN at 3-GHz VLA-COSMOS. The purpose of this project is to explore the differences in the radio structure between FRIs and FRIIs and relate them to the large-scale environment. As environmental probes we take the X-ray groups (hundreds kpc) and the density fields (~Mpc-scale) in COSMOS. We find that the large-scale environment does not explain the observed dichotomy in jet- and lobe-like FR-type objects as both types are found on similar environments, but it does affect the shape of the radio structure introducing bents for objects closer to the centre of an X-ray group.

Gamma-ray emission from radio galaxies

Sahakyan, Narek

Fermi-LAT has recently detected gamma-ray emission from active galactic nuclei which do not show clear evidence for optical blazar characteristics or having jets pointing away from the observer (radio galaxies). These are interesting gamma-ray emitters providing an alternative approach to studying high energy emission processes. I will report on a detailed investigation of the gamma-ray emission from 21 radio galaxy, including eleven FRI and ten FRII radio galaxies/SSRQs based on the Fermi-LAT data accumulated during 2008-2015. Possible spectral changes above GeV energies are investigated with a detailed spectral analysis and the gamma-ray flux variability is studied using different light curves. The gamma-ray emission properties of the considered sources are compared with similar properties of blazars (their parent population). Also, the gamma-ray emission features of the individual sources will be discussed, for example, the rapid gamma-ray variability of NGC 1275, the emission from 3C 120 jet at small (nuclear region) and large scales (knots), etc.

Discovery of a dying, giant radio galaxy in the distant Universe

Wadadekar, Yogesh

We report the discovery of a intriguing relic Giant Radio Galaxy (GRG) J021659-044920 at redshift z~1.3 that exhibits large-scale extended, nearly co-spatial, radio and X-ray emission from radio lobes, but withoutdetection of Active Galactic Nuclei core, jets and hotspots. The total angular extent of the GRG at the observed frame 0.325 GHz, using Giant Metrewave Radio Telescope observations is found to be ~2.4 arcmin,that corresponds to a total projected linear size of ~1.2 Mpc.The integrated radio spectrum between 0.240 and 1.4 GHz shows high spectral curvature with sharp steepening above 0.325 GHz, consistent with relic radio emission that is ~8 X 10^6 yr old. The radio spectralindex map between observed frame 0.325 and 1.4 GHz for the two lobes varies from -1.4 to -2.5 with the steepening trend from outer-end to inner-end, indicating backflow of plasma in the lobes. The extended X-ray emission characterized by an absorbed power law with photon index ~1.86 favours inverse-Compton scattering of the Cosmic Microwave Background (ICCMB) photons as the most plausible origin.Using both X-ray and radio fluxes under the assumption of ICCMB we estimate the magnetic field in the lobes to be 3.3 microG. The magnetic field estimate based on energy equipartition is ~3.5 microG. Our work presents a case study of a rare example of a GRG caught in dying phase in the distant Universe.

Quasar activity in the neighboring Universe

Bettoni, Daniela

We analyzed the properties of the close environments of a sample of low redshift quasarsto investigate the role of interactions for triggering and fueling the QSO phenomenon.We present the results of an extensive spectroscopic campaign at GTC and NOT telescopes in La Palma aimed at deriving the properties of companion galaxies of quasars anddetecting signatures of recent star formation both in the host galaxies and in the companion galaxies.The sources are drawn from a large (~400) sample of  (z<0.4) quasars extracted from the SDSS "Stripe 82" for which we previously investigated the host galaxies and the large scale environments properties.We found that the close (<100 kpc) companion galaxies are often associated to the QSO but  only a modest recent star formation is present. The implications for the mechanisms ofnuclear activity are briefly discussed.

The Evolution of Radio AGN in XXL-S

Huynh, Minh

The XXL is the largest survey ever with the XMM-Newton X-Ray telescope, comprising 6.9 MS spread over two 25 sq deg fields, the XXL-N and XXL-S. The main goals of the XXL project are to probe cosmology using galaxy clusters and to study galaxy evolution with a large sample of AGN. As part of the ongoing multiwavelength followup to achieve these science goals, radio observations at 2.1 GHz were obtained on the Australia Telescope Compact Array covering the full 25 sq deg of the southern field, XXL-S, reaching an rms noise of ~40 microJy with a resolution of ~5 arcsec. We identify 6287 radio sources down to 5 sigma over 25 sq deg, and find 4758 (75.7%) have an optical counterpart. Using a variety of multiwavelength diagnostics including X-Ray luminosities, MIR colours, SED fits, optical emission lines and radio luminosity, we classify the sources into three types: low-excitation radio galaxies (LERGs), high-excitation radio galaxies (HERGs), and star-forming galaxies (SFGs). We present AGN radio luminosity functions from the ATCA XXL-S for z = 0 to 1.3 and quantify the cosmic evolution of the LERG and HERG populations. Using scaling relations to convert radio jet power to kinetic energy, we also quantify radio-mode feedback across z = 0 to 1.3.

AGN parameters in the ELAIS field using CIGALE

Suleiman, Nofoz

We present a sample of AGN galaxies in ELAIS N1 field at various redshifts. We combined the new Herschel point source catalogue data with Sloan Digital Sky Survey (SDSS), 2MASS, Spitzer, WISE and other archival photometry data, creating spectral energy distributions (SEDs) that cover the rest-frame wavelength range from far-UV to far-IR (from 0.15 to 160 micrometer). The SEDs were modeled using the CIGALE software, deriving galaxy properties with a high reliability by fitting the attenuated stellar emission and the related dust emission at the same time. We also compared our results to former studies (without the new Hershel photometry and using MAGPHYS), especially focusing on the star formation rate, stellar mass, dust luminosity and dust attenuation. The comparison shows minor differences in the stellar mass, and dust attenuation, but significant differences in dust luminosity. Differences in the star formation rate were also seen at some galaxies.

Relativistic MHD rotating spine jets in Kerr metric

Tsinganos, Kanaris

By using a nonlinear separation of the variables of the general relativistic MHD equations, we construct a semi-analytic model of magnetohydrodynamic jets around rotating black holes. The model provides axisymmetric solutions, which describe the outflow in the spine jets of Active Galactic Nuclei (AGN) or Gamma Ray Bursts (GRB). These spine jets start at the exobase, at some distance above the black hole. The composition of the jet can be hadronic, if the plasma originates from the accretion disk, or leptonic if it is induced by in-situ pair production. Both hypotheses can be tested in order to distinguish which one is more realistic for the composition of the spine jet in terms of temperature and expected radiation. This model allows to constructing full MHD solutions describing the plasma outflow from the horizon to infinity. 

The New Variability Phase of OJ 287 and Emergence of New Components in NIR to X-ray Region

Kushwaha, Pankaj

We present a multi-wavelength (MW) spectral and temporal study of the recent activity of the claimed super-massive binary black system OJ 287 since December 2015. The overall MW activity can be divided into two durations: December 2015 – May 2016, showing strong activity from near-infrared (NIR) to gamma-rays and  April 2016 – July 2017, showing intense NIR to X-ray variability concurrent with detection at very high energies (VHE) by VERITAS, but without any signatures of variability  in the Fermi-LAT band. In the first duration, the variations are almost simultaneous and the SEDs show new components in NIR-optical and optical-UV region. The NIR-optical bump is consistent with standard accretion disk description while the optical-UV appears consistent with contributions from the broad-line region. The extracted broadband SEDs also show a clear shift in gamma-ray SED peak and can be explained with inverse Compton scattering of photons from the optical-UV bump. In the second period, the variations are also simultaneous except for one duration during which X-ray leads the optical/UV by ~ 5-6 day. The broadband SEDs, on the other hand, show mixture of a typical OJ 287 SED and an HBL SED, consistent with an origin from two different zones, one located at sub-parsec scales and other at parsec scales.

Accreting supermassive black holes, their jets and their nuclear environment at z~0: A multi-wavelength study including GMRT, ASTROSAT, ATCA and Chandra

Shastri, Prajval

We will present results from a multi-wavelength investigation of very nearby accreting supermassive black holes that seeks to understand the interaction between accretion, jets and the host galaxy environment, and test the hypothesis that imprints of AGN feedback are present at z~0. Our sample contains about 130 AGN which were chosen to have redshifts less than 0.02. Consequently our typical imaging has several spatial resolution elements across the host galaxy. We have completed optical IFU measurements for all the 130 objects in our sample and have some radio imaging  for a majority.  Results for individual objects as well as two data release papers from this study (the ‘S7’ project) have been published. We take this investigation further by adding GMRT imaging and archival VLA imaging for subsets of this sample,  and also ATCA, ASTROSAT and Chandra observations for select objects. Our most recent results include Far-UV imaging with ASTROSAT of a galaxy in a rich cluster environment, and Chandra imaging of a dual AGN system. Systematics for the whole sample including the relationship between the radio jets and the nuclear environment will also be presented.

Understanding the Origin of Nuclear Activity in Low-Power Radio Galaxies

Lin, Yen-Ting

Using large samples containing nearly 2300 active galaxies of low radio luminosity (1.4 GHz luminosity between 2x1023 and 3x1025 W/Hz, essentially low-excitation radio galaxies) at z<0.3, we present a self-contained analysis of the dependence of the nuclear radio activity on both intrinsic and extrinsic properties of galaxies, with the goal of identifying the best predictors of the nuclear radio activity.  While confirming the established result that stellar mass must play a key role in the triggering of radio activities, we point out that for central, most massive galaxies, the radio activity also shows a strong dependence on halo mass, which is unlikely due to enhanced interaction rates in denser regions in massive, cluster-scale halos.   We thus further investigate the effects of various properties of the intracluster medium (ICM) in massive clusters on the radio activities, employing two standard statistical tools, Principle Component Analysis and Logistic Regression.  It is found that ICM entropy, local cooling time, and pressure are the most effective in predicting the radio activity, pointing to the accretion of gas cooling out of a hot atmosphere to be the likely origin in triggering such activities in galaxies residing in massive dark matter halos.  Our analysis framework enables us to logically discern the mechanisms responsible for the radio activity separately for central and satellite galaxies.

XMM-Newton and Swift monitoring of the ISP blazar ON 231 in outburst state

Kalita, Nibedita

We present the temporal and spectral study of the intermediate type blazar, ON 231 during the outburst phase in June 2008. The source showed multiple X-ray flares in that period, while the flux amplitude varies in the range of ~ 27 - 38% with 100% duty cycle estimated from genuine IDV analysis. We find that the source showed strong emission in the lower energy bands (below 3-4 keV). All the soft X-ray bands were well correlated, while a time delay of -600s between the 0.3 - 0.5 keV and 3-10 keV bands was observed with DCF analysis. A "softer when brighter" behavior is evident from the hardness ratio light curve. The spectra cannot be described by a simple power-law model. However, a more complex model like broken power-law or a log parabolic model gives acceptable fit only up to the synchrotron component. In addition, a time-resolved spectroscopy of the flares has been carried out.

Spectral evolution of Hydra A jets: relativistic MHD-spectral simulations

de Gouveia Dal Pino, Elisabete

We present our study of the spectral evolution of the bright jet knots and the flaring zones of the iconic radio source Hydra A. The key features we focus are that the knots with gradually increasing brightness along downstream and significantly bright flaring zones. First, we developed an axisymmetric jet-intracluster medium interaction model utilising the relativistic magnetohydrodynamic module of the publicly available code PLUTO. The parameter space of the jet and the cluster environment is set based on our previous study (Nawaz et al.) of the source. The key feature of our model is that the bright jet knots of Hydra A are formed when over-pressured supersonic jets interact with the environment through a series of reconfinement shocks. In order to produce realistic emission map, we further developed a spectral evolution code. Here, we track the evolution of a distribution of non-thermal particles both spatially due to advection along the jet and energetically due to adiabatic process and synchrotron cooling. Preliminary results of the calculation of surface brightness of the simulated Hydra A jets show that in the early stage  the knots are gradually  brighter due to increasing downstream magnetic pressure.

JVLA imaging of Heavily obscured, Hyperluminous quasars

Patil, Pallavi

The active galactic nucleus (AGN) phenomenon, driven by accretion onto supermassive black holes, influences the formation and subsequent evolution of galaxies and their constituent stars, gas, and dust via radiative and mechanical energy transfer (termed AGN feedback) to the surrounding interstellar and intergalactic media. Dust obscured quasars are likely going through early stages of feedback due to recent triggering of AGN activity, thus they are ideal for studying such interactions. We present high-resolution JVLA imaging of 156 hyper-luminous and heavily obscured quasars found at redshifts from z ~ 0.4-3.  These galaxies were selected to have extremely red MIR-optical colors in WISE and bright, compact radio emission in NVSS/FIRST. JVLA snapshot observations at 10GHz with sub-arcsecond-scale angular resolution revealed that 115 out of 156 sources are indeed compact, radio-loud, and have structures on scales = 2 kpc (at z~2). We performed a detailed analysis of the radio SEDs of our sample sources. A few sources have peaked radio spectra, and thus belong to the class of High Frequency Peakers (HFP), Gigahertz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) radio sources. This suggests that the radio jets could be recently triggered and are clearing their way out of the dense ISM of the host. We discuss implications of this study for our understanding of the impact of young jets on the evolution of the host galaxy.

The highly polarized 2-90 microns core of Cygnus A

Lopez Rodriguez, Enrique

Near- to mid-infrared (NIR, MIR ; 1-13 µm) total and polarized flux observations from the ground have been key to advance our understanding about the dust distribution and emission in the central few parsecs of active galactic nucleus (AGN), i.e. jets and dusty torus. Although 10 µm total flux observations of the identified thermal and non-thermal nuclear source of radio-quiet galaxies show low polarizations (<1%), the radio-loud Cygnus A galaxy shows a highly polarized, ~10%, core. The polarization is thought to arise from a synchrotron polarized pc-scale jet close to its core with a cut-off frequency at far-IR wavelengths (FIR).  However, the atmosphere is opaque to the FIR wavelength range and observations are impossible from ground-based telescopes. Furthermore, polarimetric capabilities have been very limited in this wavelength range, which makes difficult to observationally constrain our previous findings. HAWC+ onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) has opened a new window to explore AGN, providing the best angular resolution and the unique polarimetric capability within the 50-250 um range.We here present 53 and 89 µm imaging polarimetric observations using HAWC+/SOFIA of Cygnus A. We have found a highly polarized core, ~10%, with a potential change in the polarization angle from 2 µm to 89 µm showing a shift of >50 degrees from the radio axis. Our preliminary analysis shows that a synchrotron polarized component explains acceptably well the polarized SED, however dust scattering from large grains can also be considered.

Inflow and Outflow meridional self-similar MHD models around Kerr hole

Loic, Chantry

The jets produced by AGN are extremely energetic natural phenomena and thus constitute a real laboratory of high energy physics. To describe the inner-spine jet of AGN in the context of ideal, stationary and axial-symetric MHD, we build a meridional self-similar model in Kerr metric. The choice of this metric is justified in order to describe the flow near the super-massive central black hole, and in particular to study the effects of its rotation. The model, characterized by 8 parameters, is based on a first order expansion of the governing general relativistic equations in the magnetic flux function around the symmetry axis of the system. Using the regularity conditions at the Alfvén transition surface, we introduced a parameter to take into account the light cylinder effects and the meridional increase of the Alfvén number with the magnetic flux function. This complete treatment for an outflow in a Kerr metric allowed us to present four enthalpy driven solutions with different field geometries and Lorentz factors, wherein the contribution of the Poynting flux is rather small. The jet power of the ultra-relativistic outflow solutions are of the same order as that determined from numerical simulations conducted by several groups.Furthermore, our model is able to describe both an incoming and outgoing flow at the level of the stagnation radius; at this radius, pairs are created from neutrinos or highly energetic photons coming from the disk. Coupling inflow and outflow models allows us to describe the MHD flow from the horizon of the black hole up to infinity. We can estimate the different contributions of each of those processes: at the black hole level the energetic component coming from the Blandford-Znajek effect or the generalized Penrose mechanism, and the energetic input due to the creation of pairs.

ISM and AGN Study in the Environment of Radio Galaxies using ALMA Observations

Wibowo, Ridlo

Powerful radio-AGN are mostly hosted by massive early-type galaxies (ETGs), which frequently reside in a dense concentration of galaxies. These galaxies are normally very poor in molecular gas. The gas is usually detected as a circumnuclear disk necessary to feed the accretion disk around the central supermassive black hole, generating the nuclear activity. Dust emission is mainly detected in the far-infrared (FIR) which is assumed to be thermal and originated from heating processes either by young massive stars or by the active galactic nuclei (AGN). Different mechanisms were proposed to explain the origin of these emissions but their respective contributions are not yet conclusive. ETGs have shown no independent evidence of high star formation rates, suggesting that either the older stars or the AGN are responsible for much of the FIR emission. One also argued that in ETGs the gas is unrelated to the stellar populations and favor an external origin of the molecular gas. It is then crucial to study the ISM properties of the host galaxy and also the galaxies around it, to be able to understand the creation, evolution, and feedback of the radio sources with their environment. In this study, we examine some of the most powerful radio galaxies (RGs) observed by the Atacama Large Millimeter/submillimeter Array (ALMA), which offers unprecedented sensitivity and high spatial resolution, to investigate particularly the environment of RGs. We exploit the data from the calibration observations performed for each science project of ALMA. By combining the accumulated compatible data and careful analysis of the noise and possible bias, we must be able to obtain deep submillimeter images with a sufficiently low noise level at tens µJy. We measure the thermal and synchrotron emission in the central RGs and in the field, to study the distribution of the ISM and the interplay between the central AGN and its environment. We also detect several absorption lines towards these RGs.

A New Generation of AGN Feedback Models in Simulation of Galaxy Clusters

Lu, Yinghe

A better understanding of feedback effects due to the central AGN (active galactic nucleus) in galaxy clusters is important for addressing the cool-core problem, in which the cooling rate inferred from the observed luminosity predicts far more cool gas than X-ray spectroscopy reveals. Aiming to investigate the environment of galaxy cluster cores with AGN feedback via three-dimensional hydrodynamic simulations, we present a novel, more physical subgrid model whichincorporates the most recent theoretical improvements in accretion disk physics, including information from global accretion disk simulations, jet-environment interaction, and radiative cooling. We will discuss results from a series of kiloparsec-scale simulations of galaxy cluster cores and observations that are used to calibrate the model. The studyprovides a clearer image of the detailed interplay between the supermassive black holes (SMBHs) at the centers of galaxy clusters and the surrounding gas, and offers insights into the physics of the SMBHs and the interstellar medium of cluster central galaxies. 

Radio Morphology as a Probe of the Environment: the Radio Galaxy 3C 382

Slavcheva-Mihova, Lyuba

We present a study of the interaction of the radio structures in the FR II BLRG 3C 382 with the environment.According to colour maps and 2D decomposition of the optical images, 3C 382 is E or S0 galaxy. There is a couple of filaments to the northeast-east (NE-E), another one to the south (S), and a complex of arcs in the circumnuclear region that all appear blue. The NE filaments manifest a notable match with the radio structure and the S filament traces the location of the opposite lobe displacement.The velocity of the warm absorber outflow in 3C 382 is of the order of 103 km s-1. The jet Eddington ratio exceeds the critical one regarding feedback. Thus, not only positive feedback is not expected, but the jet, driving the outflow, meets the criterion for an effective negative feedback.There is an object at the origin of the S filament that is most probaby a star. Besides, a galaxy is closely projected to the N hotspot. The redshift derived from our optical spectra shows that it is a physical companion.The hotspot spectra on both sides of 3C 382 are similar giving rise to the idea of a single injection spectrum. We suggest that the NE filament gas interacts with the jet and deflects it; light jets can be easily bent by diffuse medium. The S filament, on its turn, interacts with the backflowing plasma of the opposite lobe and causes its offset. The disturbed features in the galaxy are of tidal origin. The filaments represent gas stripped off the companion or/and resident in the body of 3C 382 in the course of interaction. Both the bar and disturbed spiral structure of the companion may be induced by the interaction with 3C 382.The lifetime of such tidal features is of order of a few 108 yr up to 109 yr, while FR II jet lifetime is up to about 108 yr. Thus, it is reasonable for the filaments to precede the jet, which makes this scenario viable. This may also mean that the interaction with the companion can be related to the onset of nuclear activity of 3C 382.

AGN vs starburst: growing a black hole in a compact star-forming galaxy

Goncalves, Thiago

In this talk, I will present the result of a recent observational project using ALMA to investigate the properties of the molecular gas in low-redshift (z~0.2) ultraviolet-luminous galaxies. These objects are extremely dense, highly star-forming and very metal-poor compared to other galaxies of similar stellar mass at the same redshifts, justifying their use as analogues to distant main-sequence galaxies in an attempt to understand the interplay between gas and star formation under similar conditions in the early universe. We have observed one object in this sample with high spatial resolution, comparing data from CO emission and hydrogen recombination lines down to a resolution of ~400 pc, allowing for a detailed analysis of the conversion of gas into new stars. In particular we are able to compare star formation laws in individual clumps and the surrounding ISM, highlighting the difference between star formation efficiencies in each environment within the galaxy. More specifically, we can investigate in extreme detail the central star-forming region where AGN activity is present (as indicated by x-ray observations), although the bolometric luminosity of this region is dominated by star formation activity. This presents a unique opportunity to investigate the establishment of the m-sigma relation in central bulges while star formation is still active.

Probing the gas fuelling and outflows in nearby AGN with ALMA

Audibert, Anelise

Feeding and feedback in active galactic nuclei (AGN) play a very important role to gain a proper understanding of galaxy formation and evolution. The interaction between activity mechanisms in the nucleus and their influence in the host galaxy are crucial for the feedback and gas fuelling of the black hole (BH). Winds and outflows produced by the AGN can eject or heat the gas, terminate the star formation and through the lack of fuel for accretion, quench the black hole activity. Recent discoveries of massive molecular outflows have been promoting the idea that winds may be major actors in sweeping the gas out of galaxies, in agreement with theoretical predictions of AGN-driven winds models. AGN are fuelled by accretion of material onto the SMBH and the gas component can form stars on its way to the central engine. By studying the molecular gas in galaxy disks we want to understand: (i) how the star formation and nuclear activity are fuelled and what are the timescales involved, since both process rely on a common cold gas supply, but in different timescales? (ii) what are the mechanisms driving gas from the disk towards the nucleus, removing its large angular momentum and forming large non-axisymmetric perturbations?Our goal is to probe these phenomena by probing the gas inside the central kpc in nearby AGN. This has recently been possible due to the unique ALMA spatial resolution and sensitivity. We present a study of the morphology and kinematics of the cold dense gas in a sample of 5 nearby Seyfert/LINER nuclei at the unprecedented spatial resolution of 0.06-0.09” (3-10 pc), part of a new ALMA follow-up of the NUGA (NUclei of GAlaxies) program. NUGA is a high-resolution (0.5-1”) CO survey of 25 low luminosity AGN performed with the IRAM PdBI that has revealed smoking gun evidence of gas funnelling into the nucleus in 1/3rd of the sample, suggesting that galaxies may be alternating periods of fuelling and starvation.

Multi-wavelength intraday variability studies: what do they tell us about blazar Jets?

Bhatta, Gopal

Intraday variability studies are the most important, if not the only, tools to explore the physical processes occurring at the innermost blazar regions which are not resolved by any current instruments. In this presentation, we report the results of intraday variability in the optical (BVRI bands) and hard X-ray band (3-79 keV) in a number of blazars consisting of both BL Lacs and flat spectrum radio quasars. In the optical microvariability studies of low-synchrotron peaked blazars S5 0716+714 and BL Lac, we observed many interesting features such as rapid variability, large variability amplitude, presence of characteristic timescales, bluer-when-brighter achromatic behavior, and single power-law power spectral density. In 31 NuSTAR observations of 13 blazars, using spectral and timing analysis, we found similar features consistent with the ones from the optical studies. In addition, in BL Lacs we estimated the Lorentz factor of the population of highest energy electrons emitting synchrotron emission, and whereas in flat-spectrum radio quasars, using external Compton models, we estimated the energy of the lower end of the injected electrons to be a few Lorentz factors. In addition, we find that the low flux state exhibit more rapid variability in contrast to the previously reported results showing high flux states displaying rapid variability. In both the studies, the size of the emission regions estimated using variability timescales turn out to be an order magnitude smaller than the gravitational radius of a typical black-hole masses between 10^8-10^9 solar masses which are believed to be harbored by the radio-loud AGN. The results of the studies suggest that these low-amplitude rapid variability might originate as a result of magnetohydrodynamical instabilities near the base of the jets triggered by the processes modulated by the magnetic field at accretion disc.

Multi-wavelength Observations of Dual AGN (MODA) – the cases of Mrk463 and NGC6240

Treister, Ezequiel

Nowadays, we know that most Active Galactic Nuclei (AGN) are observed to be triggered by internal, secular processes and minor galaxy mergers. Nevertheless, the most luminous AGN – quasars (QSOs) – are hosted by major mergers. In addition to that, AGN activity in mergers is seen to peak at nuclear separations shorter than 10kpc. Non intuitively, the number of AGN pairs found at those distances (also known as dual AGN) are not frequently identified: only a few percent of mergers host such systems. Although technical limitations may play some role in this, system-intrinsic physical properties definitely will (e.g., AGN duty-cycle shorter than that of mergers; extreme nuclear obscuration; etc...). As a result, we are conducting the Multi-wavelength Observations of Dual AGN (MODA) survey targeting 17 known dual AGN systems at z<0.1 and aims to characterize their physical properties of the ionized, atomic, and molecular gas, as well as the dust. This presentation will present the results on Mrk463 reported by Treister et al. (2018), where optical, near-infrared and ALMA millimeter observations were brought together to reveal the large and small scale properties of the system. Specifically, the evidence for a biconical outflow and ionized material outflowing at >600 km/s (a rate in rough balance with the molecular gas infalling onto the system), and an AGN-photoionized region indicating that the Eastern nucleus was up to 20 times more active in the past 10's thousand years. In addition, the current work being done toward NGC6240 will also be revealed, where ALMA data is resolving the gas bridging the two AGN nuclei down to ~25pc scales.

Direct evidence of a few to tens parsecs torus in 3C84

Kawakatu, Nozomu

New discovery of a parsec scale northern lobe in a nearby bright radio galaxy 3C 84 at 43 and 86 GHz shades a light on the nature of structure surrounding of active galactic nuclei (AGNs). Based on this, we examine a parsec scale surrounding matter near supermassive black holes (SMBHs) of 3C 84.The optically thick spectral feature of northern lobe can be interpreted as the existence of a dense matter, which is responsible for the free-free absorption of the northern lobe with the ionized electron density with 10^5 cm^-3. Moreover, the ratio of the observed optical depths at 43 and 86GHz suggests highly inhomogeneous surrounding matter near SMBHs within a parsec scale. In addition to this, the abrupt appearance of the new counter lobe implies the column density with N_H~10^23-24 cm^-2 for inclination angle 40-80 deg. This would be consistent with results of the radiation-driven fountain model for low-luminosity AGNs(Wada 2012). Thus, this may suggest that the observed absorbing structure is a direct evidence of the clumpy torus.

Disentangling radio galaxy magnetism with the QUOCKA Survey

Heald, George

I will introduce the QUOCKA survey: QU Observations at Cm wavelength and Km baselines with the ATCA (Australia Telescope Compact Array). The aim of the QUOCKA survey is to provide a gold-standard set of broadband radio polarization spectra for active galactic nuclei (AGN) in the southern sky. QUOCKA will build on, and complement, the ASKAP POSSUM survey via targeted full-polarization imaging observations covering the 1-8 GHz range. The primary science goals are to: (i) characterise the internal magnetic field and plasma structure of radio lobes, jets, and their environments from exquisite broadband linear polarization spectra; and (ii) perform the first large-scale search for and characterisation of broadband circular polarization from radio galaxies. QUOCKA observations begin in mid-2018 with an initial sample of 250 radio galaxies selected from ASKAP Early Science fields. I will summarise the observational progress, demonstrate the data quality, and present initial results from the survey.

Gas kinematics in radio-AGN

Xu, Dawei

Narrow-line Seyfert 1 galaxies are a sub-class of active galactic nuclei (AGN) with low-mass black holes and high accretion rates. Only a small fraction of them is radio-loud. Our analysis of SDSS spectroscopy of these galaxies has shown that their emission lines are highly shifted. If interpreted as outflow, these imply radial velocities exceeding up to 2000 km/s in the highest-ionization gas. We further find a strong ionization stratification, and a lack of zero-velocity high-ionization gas, implying a large NLR fraction is affected by the outflow. All galaxies of the mini-sample have high L/LEdd and also possess strong radio jets. Therefore, both mechanisms are potential drivers of the outflow, i.e., large-scale winds and jet-NLR interactions. Based on predictions from hydrodynamic simulations, the high observed outflow velocities can be understood, if the AGN are in an early stage of their evolution, not much older than 1 Myr.

The continuing mystery of multiple spectral components in Jets from Black Holes

Meyer, Eileen

One of the first things that astronomers usually determine for any new astrophysical source class is the emission process generating the radiation -- thermal, synchrotron, inverse Compton, Bremsstrahlung, etc.  Identifying these processes is critical to using the EM observations to probe the physical environments of very distant objects.  Despite the fact that jets from black holes were first understood to exist over 40 years ago, we are still in ignorance about many primary aspects of these systems -- including the radiation mechanism at high energies, the particle makeup of the jets, and how particles are accelerated, possibly to energies as high as 100 TeV and hundreds of kpc from the central engine.  I will discuss how this mystery first really got going with the launch of Chandra in 1999, and show how high-resolution observations with observatories like Hubble and ALMA have continued to add pieces to the puzzle -- sometimes seemly solving a problem, and other times opening a new one. I will conclude with some perspectives on how new observatories, like the Chandra successors AXIS and Lynx, can help us solve these long-open questions in jet physics.

The seed factor: a way to understand the blazar GeV emission

Georganopoulos, Markos

The question of if the blazar GeV emission comes from leptonic or hadronic processes is still unclear. For leptonic models the distance of the GeV emission site is still debated. We present a way to approach these issues and we show some preliminary results.

Multi-wavelength Variability and QPOs in Blazars

Gupta, Alok

In the present poster, I will summarize our recent results based on multi-wavelength variability and QPOs detection in blazars.

Radio luminosity function at z = 6

Saxena, Aayush

We present a model to predict the luminosity function for radio galaxies and their linear size distribution at any redshift. The model takes a black hole mass function and Eddington ratio distribution as input and tracks the evolution of radio sources, taking into account synchrotron, adiabatic and inverse Compton energy losses. We first test the model at z = 2 where plenty of radio data are available and show that the radio luminosity function (RLF) is consistent with observations. We are able to reproduce the break in luminosity function that separates locally the Fanaroff–Riley class I and Fanaroff–Riley class I radio sources. Our prediction for linear size distribution at z = 2 matches the observed distribution too. We then use our model to predict an RLF and linear size distribution at z = 6, as this is the epoch when radio galaxies can be used as probes of reionization. We demonstrate that higher inverse Compton losses lead to shorter source lifetimes and smaller sizes at high redshifts. The predicted sizes are consistent with the generally observed trend with redshift. We evolve the z = 2 RLF based on observed quasar space densities at high redshifts, and show that our RLF prediction at z = 6 is consistent. Finally, we predict the detection of 0.63, 0.092 and 0.0025 z = 6 sources deg2 at flux density limits of 0.1, 0.5 and 3.5 mJy. We assess the trade-off between coverage area and depth and show that LOFAR surveys with flux density limits of 0.1 and 0.5 mJy are the most efficient at detecting a large number of z = 6 radio sources.

Optical monitoring of a sample of FR II-type QSO

Zola, Staszek

We will present results derived from a monitoring program of a sample of FR-II type radio quasars.The variabilities detected in their densly covered light curves, that have being gatheredover a period of more than 9 years, are analyzed with statistical methods (WWZ, DFT andthe structure function). Based on our findings we will draw preliminary conclusions on theproceses that may cause  flux variations in the optical band.

Radio-spectral index distribution of SDSS-FIRST sources across optical diagnostic diagrams

Zajacek, Michal

For a selection of a few hundred intermediate-redshift SDSS-FIRST galaxies, we performed radio-continuum observations at 4.85 and 10.45 GHz with the Effelsberg 100-m telescope. The selected sources cover mainly the Composite-AGN part in the optical diagnostic diagrams (ODDs). The ionization-state information and the radio loudness at 1.4 GHz was complemented by spectral-index distribution between 4.85 and 10.45 GHz. We performed an extensive analysis of the distribution of steep, flat, and inverted radio sources across ODDs. Three main classes of objects were found: (i) sources with steep radio index, high ionization ratio and large radio loudness, (ii) sources with flat radio index, lower ionization ratio and intermediate radio loudness, and (iii) sources with inverted radio spectra, low ionization ratio and low radio loudness. The groups (i), (ii), and (iii) are prominent on the transition from Seyferts to LINERs in the direction of the decreasing ionization-line  ratio, where the trend of radio-spectral index flattening is found. These findings are interpreted in terms of the recurrent nuclear/jet activity, partially driven by galaxy interactions and mergers.

Kinetic Simulations of the Radiative Signatures of Relativistic Magnetic Reconnection

Nalewajko, Krzysztof

We present the results of kinetic numerical simulations of relativistically magnetized plasmas that illustrate the mechanism of magnetoluminescence, i.e., efficient conversion of free magnetic energy into broad-band non-thermal radiation by means of localized magnetic reconnection and associated particle acceleration. In particular, we performed 2D and 3D particle-in-cell simulations of periodic magnetic equilibria known as "ABC fields", including radiation losses due to synchrotron and inverse Compton processes. Similar processes can be expected to operate within the relativistic jets of active galactic nuclei, leading to non-thermal radiation signals observed in blazars and radio galaxies. We calculate detailed radiation signatures including lightcurves, spectral energy distributions, and synchrotron polarization. We investigate the effect of strong radiative losses on the intrinsic structure of dynamical current layers. We also demonstrate departure of the Compton dominance parameter from its nominal value, which can be invoked to alleviate the extreme energetic constraints imposed on the relativistic jets by rapid gamma-ray flares.

3C 294 revisited

Heidt, Jochen

3C 294 is a powerful FR II radio galaxy at z = 1.786 dominated by a Z-shaped structure with a relatively weak core at 6cm. The galaxy is associated with a large cloud of ionized gas aligned with the inner part of the radio structure. Due to its proximity to a bright 11th mag star it is an ideal target for observations with modern AO-systems. Previous AO-observations of 3C 294 have resolved this source in several subclumps perhaps in the process of merging. This is supported by an apparent overdensity of faint red galaxies in its vicinity. On the other hand, there are claims that 3C 294 consists of two active nuclei separated by a few kpc based on proper astrometry and acomparison with high-resolution X-ray data. Thus its evolutionary state and structure is complex and not yet fully understood. The findings described above are based on observations more than 15 years ago. Since then the AO-systems have become more advanced and the detectors more sensitive allowing observations of this sourcewith much better contrast and sensitivity than before. In this contribution we present and discuss a new data set of 3C 294 taken at the Large Binocular Telescope. In particular, we secured deep diffraction-limited JHK-images of 3C 294 accompanied by high-resolution (0.5" FWHM) JHK-images of its large-scale environment.The data set is complemented by deep optical spectra to search for signatures of a dual AGN.

The evolution code PEGASE.3 for distant radiogalaxies with JWST

Rocca Volmerange, Pr Brigitte

New observations (images and spectra) of distant radio galaxies with the satellite JWST on its unique wavelength coverage (visible to mid-infrared) and resolutions will require galaxy evolution models with dust attenuation and emission. The code PEGASE.3 (Fioc & Rocca-Volmerange,, on submission process) is specifically adapted to interpret JWST data, in particular in the puzzling 5 to 20 microns domain. Multiple aims are to identify stochastic effects on dust emission as well as to disentangle the various components from hot dust, star-formation zones, diffuse ISM and AGN torus, in possible relation with the growth of super massive black holes.

The reconfinement of AGN jets

Bamford, Thomas

The relativistic jets associated with active galactic nuclei (AGN) are capable of propagation over multiple length scales, extending up to a few billion initial jet radii. This remarkable stability can be understood in terms of the interaction of the jet with its surrounding environment. In particular, jet expansion associated with a decreasing external pressure can lead to causal disconnectivity across the jet, suppressing global instabilities. In at least some AGN jets, the external pressure eventually drives a reconfinement shock into the jet axis establishing causality across the jet once more. Past this reconfinement point the jet is therefore subject to global instabilities and will eventually become fully disrupted and turbulent. In 1997 Komissarov and Falle proposed a semi-analytic model predicting the position of the reconfinement point. This model is explored in more detail for different atmospheres. Strong deviations are found for steeply declining power law atmospheres, with the model significantly underestimating the reconfinement scale.

Radio-loud fraction of high-z low-luminosity HSC/Subaru quasars

Lee, Kianhong

The co-evolution between super-massive black holes (SMBHs) and their host galaxies has become one of the biggest mysteries in the modern astronomy. In the active galactic nucleus (AGN)-feedback scenario, theoretical studies show that the radio-mode feedback has a significant impact on shaping the bright-end of the galaxy luminosity function. Radio-loud AGNs, a sub-class of AGN populations, provide a laboratory to study the physical processes associated with the radio-mode feedback in galaxies, yet we still lack a complete understanding of the existence of two populations which are divided by whether they show the strong radio emission or not.In the local or lower redshift universe, some studies showed that the radio-loud fraction tend to depend on both the redshift and the optical luminosity, while it has been argued that the result is biased by the apparent magnitudes. Such potential bias can become more significant at higher redshifts, and in fact, previous studies on radio-loudness of high-z (z>5.5) quasars are focused on the very luminous ones which likely host heavy SMBHs.However, recently, a sample of more than 80 high-z (z~6) lower luminosity quasars has been discovered by an on-going deep and wide-area multi-band optical imaging survey with the Hyper Suprime-Cam (HSC) on Subaru 8-m telescope (Matsuoka et al. 2016, 2018ab). Most of these newly uncovered z~6 quasars have the lower rest-UV luminosity (M_1450 > -25 mag) and thus fall near the break of the quasar luminosity function at z~6, which means that their properties are more representative compared to the known luminous ones in the early universe.Toward this valuable new sample, we have conducted radio follow-up observations with JVLA at 1.4 GHz. At this moment, 16 targets have been observed with a typical sensitivity of about 10-30 uJy (1 sigma). In this presentation, constraints on the radio-loud fraction of such low-luminosity z~6 quasars will be presented for the first time.

High-resolution VLBI observations of Active Galactic Nuclei

Ros, Eduardo

Active Galactic Nuclei are probed at sub-parsec scales by very-long-baseline interferometry (VLBI) at the highest resolutions.  These are reached by the RadioAstron program with baselines larger than the Earth with a radio telescope in orbit; and also observing at high frequencies with the Global mm-VLBI Array (GMVA, 86 GHz) and the Event Horizon Telescope (EHT, 230 GHz).  For the latter, the inclusion of beam formed ALMA since April 2017 provides enhanced sensitivity and imaging fidelity.  In this poster we will show selected results of our observations of the innermost regions of the radio galaxies NGC 1052 and Centaurus A, and blazars such as 4C+01.28, among others. 

XXX IAU General Assembly | ACV - Austria Center Vienna  | Bruno-Kreisky-Platz 1  | 1220 Vienna