Focus Meeting 3 - Abstracts
Radio galaxy populations and their cosmic evolution
Sadler, Elaine
Large-area radio surveys, combined with wide-field imaging and spectroscopic surveys at optical and other wavelengths, have allowed us to build up a detailed picture of the different radio-galaxy populations in the local Universe and improve our understanding of how these populations evolve with cosmic time. I plan to review recent progress in this field, with a particular focus on the results from multi-wavelength radio surveys enabled by new telescopes and capabilities.
Finally Rapporteur
Celotti, Anna Lisa
.I will try to enlighten the content of the FM3, with emphasis on still open problems.
The event horizon telescope and beyond
Doeleman, Sheperd
The Event Horizon Telescope (EHT) is a Very Long Baseline Interferometry (VLBI) array operating at the shortest possible wavelengths, which can resolve the event horizons of the nearest supermassive black holes. Initial observations with the EHT have revealed Schwarzschild radius scale structure in SgrA*, the 4 million solar mass black hole at the Galactic Center, and in the much more luminous and massive black hole at the center of the giant elliptical galaxy M87. Over the coming years, this international project will add new sites, increase observing bandwidth and continue observations to focus on astrophysics at the black hole boundary. The EHT will have an unprecedented combination of sensitivity and resolution with excellent prospects for imaging strong GR signatures near the horizon, detecting magnetic field structures through full polarization observations, time-resolving black hole orbits, testing GR, and modeling black hole accretion, outflow and jet production. This talk will review progress and status of the project and describe future enhancements, including potential addition of space-based dishes to the array.
Disks, jets, and other black hole-powered transients
Tchekhovskoy, Alexander
Black holes are responsible for a wide variety of astrophysical phenomena. They devour stars, eject relativistic jets, affect star formation and galaxy evolution, and enrich the Universe with heavy elements. I will discuss how global general relativistic magnetized fluid dynamics numerical simulations allow us to use this activity to quantitatively probe strong-field gravity and constrain black hole physics in various astrophysical contexts.
AGN Feedback in Clusters of Galaxies
Fabian, Andrew
Accreting black holes in Brightest Cluster Galaxies power jets whichblow bubbles in the surrounding intracluster medium. Such AGN Feedbackis commonly observed as radio-emission-filled cavities in ChandraX-ray images of cool core clusters. Good agreement is obtained betweenthe feedback power determined from the bubbles and the rate ofradiative energy loss from the hot gas in the core. Catastrophiccooling of the intracluster gas is thereby prevented. I discuss howthe energy can be transported and dissipated throughout the clustercore. Feedback operating in this way appears to be ubiquitous inearly-type galaxies, groups and cool core clusters over a wide rangeof mass and redshift.
Prevalence of radio jets associated with quasar outflows and feedback
Jarvis, Miranda
We have identified that radio jets are commonly associated with ``radiative mode” feedback. By performing a systematic multi-wavelegnth study of z<0.2 quasars, we have found that >~70% of `radio quiet’ type 2 quasars, that host kpc-scale ionized gas outflows, exhibit radio jet structures. I will present our results on the pilot sample of 10 objects that combine high resolution (~0.3-1 arcsec) radio imaging at 1-6GHz with optical IFU observations. Our results demonstrate that is it extremely common for jets to be spatially and kinematically linked to kpc-scale ionized gas kinematics in such quasars. Therefore, radio jets may be an important driver of outflows during `radiative mode'’ feedback, apparently blurring the lines between traditional divisions of feedback modes. Based on a recently accepted VLA proposal our sample should reach ~50 quasars during 2018. I will outline our on-going campaign to obtain multi-wavelength observations to provide a full picture of the properties, drivers and impact of galaxy wide outflows in low redshift quasars.
The parsec-scale structure of jet-driven HI outflows in powerful radio galaxies
Morganti, Raffaella
Massive outflows of atomic hydrogen in powerful radio galaxies are a striking signature of AGN feedback. Such outflows are considered to be largely driven by the relativistic jets launched by the AGN, pushing their way through the clumpy interstellar medium surrounding the AGN. However, information on the complex interplay on parsec-scales between gas and jets, and how this evolves with time, is extremely limited. Progress can be made by using Very Long Baseline Interferometry (VLBI) which provides the spatial resolution required. We have conducted a study to locate and characterise the outflow of atomic gas on parsec scales in a small, but diverse sample of young and recently restarted radio galaxies comprising 4C12.50, 3C236, 4C52.37, and 3C293. In this talk, we will compare the differences and similarities of the properties of the HI outflows in our sample which provides important input for theoretical models. Our data allow to start building up a picture of the relevant physical processes of jet-driven outflows on small scales, while our in results we may see indications for different stages of evolution in jet-ISM interactions. This shows the potential of future studies on larger samples to enable a more detailed statistical analysis.
Probing SMBH axis perturbations with low axial ratio radio galaxies
Saripalli, Lakshmi
Extended radio emission associated with AGNs has a variety of structures determined by the direction and stability in beam powers, as well as the ambient gaseous environment of the host galaxy. Radio galaxies with significant distortions and radio emission that is off the main axis exhibit low axial ratios. A significant subset of this class of low axial ratio radio galaxies may be caused by changing beam directions, which are signposts of perturbations to the super-massive black hole spin axis (SMBH; Saripalli and Roberts, 2018). I present a systematic study of an unbiased sample of radio galaxies with low axial ratios in a program aimed at (a) an empirical classification of the types of observed off-axis distortions, and (b) relating these to the types of distortions expected in interactions of beams with asymmetric gaseous environments, as well as in a variety of SMBH spin axis perturbations expected in different stages of galaxy mergers. The analysis leads to (c) derivation of occurrence rates for mergers and hence for nanoHertz GW backgrounds. The work is based on recent EVLA imaging of a large sample of low axial ratio radio sources, which has unearthed a rich haul of S-, Z- and X-shaped radio galaxies as well as a significant number that show signatures such as inner S-spines, and those that show a pair of radio sources along different axes with a common radio core. Our analysis of the large sample of 100 distorted radio galaxies points to a favored mechanism for the morphologies of the intriguing X-shaped radio galaxies that require both black-hole axis flip as well as synchrotron-plasma backflows into relic channels. The study has opened a promising route to pursue searches for binary SMBHs using large samples of low axial ratio radio galaxies, and hence to examine central engine astrophysics in extreme gravity regimes.
Molecular outflows in young radio galaxies
Oosterloo, Tom
Our view of the physical conditions of the gas in the central regions of AGN has been enriched by the discovery of fast, massive outflows of molecular gas in AGN. These outflows can be driven by radiation from the AGN, but also by the plasma jets ejected by the AGN. These outflows impact on the growth on the central supermassive black hole as well as on the star formation of the host galaxy.Much of the physics of these outflows, and their impact on the evolution of the host galaxy, is still not well understood. Better understanding these outflows, and quantifying their impact, requires tracing their location and deriving their physical conditions (density, mass, mass outflow rate and kinetic energy etc.).We will present recent ALMA observations which have allowed to study the details of the molecular outflows in two radio galaxies where young radio jets play a key role in shaping the surrounding gaseous medium. Data on multiple molecular transitions allow us to derive the physical conditions in different regions of the outflows. We will describe these results, with emphasis on the comparison with other phases of the ISM (HI and ionised gas).Based on a comparison with detailed numerical simulations, for one of the objects we obtain a complete picture of the outflow and find that outflowing molecular gas is present across the entire region co-spatial with the radio plasma, providing unambiguous evidence that the radio jets are driving the outflow. The signature of the impact of the radio jet is clearly seen in the spatial distribution of the excitation temperature and pressure of the outflowing gas, with the highest excitation and pressures found for the gas with the highest outflow velocities. The detailed information about the physical condition of the gas in this fast outflow can serve as template for the signatures of the impact of radio plasma jest on a gas-rich ISM and guide the studies of outflows in other galaxies, including higher redshift objects.
Modeling the environmental dependence of radio galaxy populations
Shabala, Stas
Feedback from AGN radio jets is held responsible for regulating star formation in the most massive galaxies over the last half of Hubble time. Observations of radio galaxy populations encode important information on feedback energetics and duty cycles, yet interpreting these observations is challenging due to the highly non-linear nature of the mapping between the observable and physical properties of radio jets.I will present a recently developed dynamical model, RAiSE (Turner & Shabala 2015, Turner et al. 2018a,b). A major departure from previous radio source models is in using galaxy clustering to describe environments into which the jets expand; this approach allows jet models to be easily integrated within a semi-analytic galaxy formation framework. The mapping between observables (such as radio luminosity) and physical parameters (such as AGN jet power and age) is strongly environment-dependent, and also evolves substantially over the AGN lifetime. I will describe the framework for inferring intrinsic jet parameters from broadband radio continuum and ancillary data, and quantifying selection effects against old low-surface brightness radio lobes such as those recently discovered with LOFAR and the MWA.
Testing jet formation in a new sample of radio galaxies
Boccardi, Bia
In the recent years, radio galaxies proved to be the the ideal targets for studies aimed at investigating the launching mechanism of relativistic jets. Inferring the intrinsic properties of the jet base through high-resolution radio observations is, in fact, easier in misaligned objects due to the reduced impact of Doppler boosting and projection effects. So far, very-long-baseline interferometry studies of jet formation have been performed in selected nearby objects (mainly in M87, Cygnus A, and 3C84), and have provided important observational evidence in support of the magnetic launching models.In this talk, I will discuss the attempt to identify a larger sample of radio galaxies suited for such analyses, and I will present first results concerning the collimation properties and the internal structure of the plasma flow in still unexplored sources down to scales of hundreds Schwarzschild radii.
VHE Gamma-Ray Observations of Radio Galaxies by H.E.S.S.
Boettcher, Markus
Only a handful of radio galaxies have been detected invery-high-energy gamma-rays with ground-based CherenkovTelescope facilities. The theoretical interpretation of the gamma-ray emission seen from these misaligned jet sources remains problematic due to the expected smallDoppler boosting (or even de-boosting). In this talk,I will review recent results from H.E.S.S. and co-ordinatedmulti-wavelength observations of radio galaxies, focusingon two prominent examples, namely Centaurus A, and PKS 0625-354. Centaurus A provides clear evidence fortwo spectral components in the combined Fermi-LAT +H.E.S.S. spectrum, while SED and variability patternsof PKS 0625-354 suggest a blazar-like jet orientation on small scales, contrasting the misaligned large-scalejet structure that led to the source's classification asradio galaxy.
The intermediate-power population of radio galaxies: morphologies and interactions
Worrall, Diana
Radio galaxies of intermediate power dominate the radio-power injection in the Universe as a whole, due to the break in the radio luminosity function, and so are of special interest. The population spans FR I, FR II, and hybrid morphologies, resides in a full range of environmental richness, and sources of all ages are amenable to study. Structures and interactions will be described, with emphasis on sources with deep high-resolution Chandra X-ray data. As compared with low-power sources there is evidence that the physics changes, and the work done in driving shocks can exceed that in evacuating cavities. The range of morphologies and phenomena will be illustrated and summarized.
Extreme jet distortions in low-redshift radio galaxies
Birkinshaw, Mark
Jets commonly display bends and knots at which the flows may change character. Some extreme distortions have implications for the nature of jet flows and their interactions. We will present the results of recent radio mapping of 3CRR and other radio galaxies. In the case of NGC 7385 the cause of the distortion is a collision with a foreground magnetised gas cloud which causes Faraday rotation and free-free absorption, and is triggered into star formation: the highly-ionized cloud in PKS 2152-699 may be similar. For NGC 6109 the distortion is more extreme, but no deflector can be identified in cold or hot gas: a similar distortion in NGC 7016 is apparently associated with an X-ray gas cavity. The results will be related to encounters with substructures in the intergalactic medium and the compositions and speeds of the jets.
Probing restarting activity in soft gamma-ray selected giant radio galaxies
Bruni, Gabriele
Cross-correlating the INTEGRAL/IBIS - Swift/BAT AGN population with radio catalogs (NVSS, FIRST, SUMSS), we found that 25% of extended radio sources are Giant Radio Galaxes (GRG), i.e. the largest individual objects in the Universe. This fraction is four time more abundant than what found in previous studies. In 2014, we observed a pilot sample of these soft-gamma ray selected GRG at low radio frequencies with the GMRT, with the aim of studying the morphological and spectral properties of these objects. Thanks to these data, we discovered the second X-shaped GRG to date, and a previously unidentified radio galaxy. Another object, observed both at kpc and pc scales (VLBI), showed an extreme jet re-orientation (about 90 degrees). Moreover, the majority of these objects show signs of restarting activity from previous observations in the literature.Given these intriguing premises, we embarked on a radio observing campaign, using both single dish (Effelsberg) and interferometers (VLBA), to probe the lifecycle of these soft gamma-ray selected GRG. The results of this campaign will be presented, that potentially shed light on the origin and evolution of the radio phase for this extreme class of objects (and radio-loud AGN in general), and the connection with high-energy emission. The X-ray properties, and in particular the correlation between the X-ray luminosity of the AGN and the radio luminosity of both the core and the lobes, will be discussed as well.
The Jet-Disk Model for the Galactic Center and other AGN
Falcke, Heino
The Galactic center host a well-known flat-spectrum radio source, Sgr A*, that is akin to the nuclei of quasars and radio galaxies. There is still some discussion on where the persistent and flaring emission of that source originates from. Does it come from an accretion flow or is it produced in a relativistic jet-like outflow? Answering this question is not only important for understanding the plethora of multi-wavelength data available for Sgr A*, it is also crucial for interpreting upcoming VLBI images of the shadow of the event horizon. Using advanced three-dimensional general relativistic magnetohydrodynamics simulations coupled to general relativistic ray tracing simulations, we can now model the dynamics and emission of the plasma around starving black holes in great detail out to several thousand Schwarzschild radii. Jets appear almost naturally in theses simulations. A crucial parameter is the heating of radiating electrons and we argue that electron-proton coupling is low in the accretion flow and high in the magnetized region of the jets, making the jet an important ingredient for the overall appearance of the source. This comprehensive model is able to predict the radio size and appearance, the spectral energy distribution from radio to X-rays, the polarization properties, the variability, and the time lags of Sgr A* surprisingly well. Most interestingly, the same model can be easily generalized to other jet sources like M87 and other radio galaxies.
Jet-driven outflows of cold gas in radio galaxies: the case of 3C293
Mahony, Elizabeth
While it is generally accepted that the evolution of galaxies and their central SMBH are strongly linked, the feedback mechanisms responsible for this are less clear. Outflows are often thought to be driven by quasar winds or massive starbursts, but an increasing number of studies have shown that radio jets could also be responsible. In this talk I will present recent results on jet-driven outflows of gas in the nearby radio galaxy 3C293. Using spectral line observations from the JVLA we detect fast outflows of neutral hydrogen of up to ~1200 km/s being driven by the radio jet at a distance of 0.5 kpc from the central core of the AGN. Follow-up IFU observations tracing the ionised gas revealed broader linewidths up to 12 kpc from the nucleus, indicating that the disturbed kinematics extend beyond the high surface brightness radio structures of the jets. These results highlight the need for deep optical and radio observations at high resolution to properly characterise the interaction between radio jets and the surrounding gas. The upcoming SKA-pathfinders will allow us to map the interaction between radio jets and the cold gas in galaxies out to further distances than ever before, shedding light on how jets impact their environment at a crucial point in the lifecycle of radio galaxies.
The MWA GLEAM 4-Jy Sample
White, Sarah
Powerful radio-galaxies feature heavily in our understanding of galaxy evolution. However, when it comes to studying their properties as a function of redshift and/or environment, the most-detailed studies tend to be limited by small-number statistics. In this talk, I will present a new sample of nearly 2,000 of the brightest radio-sources in the southern hemisphere (Dec. < 30 deg). These were observed at low radio-frequencies as part of the GaLactic and Extragalactic All-sky MWA (GLEAM) survey, which is a continuum survey conducted using the Murchison Widefield Array (MWA). This instrument is the precursor telescope for the low-frequency component of the Square Kilometre Array, and allows us to select radio galaxies in an orientation-independent way (i.e. minimising the bias caused by Doppler boosting, inherent in high-frequency surveys). Being brighter than 4 Jy at 151 MHz, we refer to these objects as “the MWA GLEAM 4-Jy Sample”. Thanks to the location of the MWA in a protected, radio-quiet zone, we have excellent spectral coverage for these sources, with 20 radio flux-densities spanning a frequency range of 72-231 MHz. By combining these measurements with those at higher frequencies, we can better investigate the processes that give rise to spectral curvature in the radio. Furthermore, we use multi-wavelength data -- such as existing optical spectra from the 6-degree Field Galaxy Survey (6dFGS) and mid-infrared images from the Widefield Infrared Survey Explorer (WISE) -- to identify the host galaxies of the low-frequency radio emission. Those with 6dFGS spectra are then used to provide first insights into the local sources with optically-bright hosts (median z = 0.09). Finally, with 10 times as many sources as the most-prominent, low-frequency radio-source sample that is optically complete (the revised Third Cambridge Catalogue of Radio Sources; 3CRR), the MWA GLEAM 4-Jy Sample will allow models of powerful active galactic nuclei to be tested more robustly.
Understanding the mechanical feedback from high- and low-accretion rate radio galaxies
Whittam, Imogen
I will discuss the properties of ~1000 radio galaxies selected from a 1.4 GHz JVLA survey of Stripe 82. This survey covers 100 deg2 and is a factor of five deeper than FIRST, allowing us to probe the fainter radio galaxy population (1.4 GHz luminosity > 1021 W/Hz). Using optical spectra we have classified the sources as high-excitation (radiative mode) or low-excitation (jet mode) radio galaxies (HERGs and LERGs). We find that the HERGs tend to have higher Eddington-scaled accretion rates than the LERGs, but that there is more overlap between the two distributions than found by previous studies at higher radio luminosities. We show that the properties of the host galaxies (e.g. stellar mass and stellar age) vary continuously with accretion rate, with the most slowly accreting sources having the oldest stellar populations, consistent with the idea that these sources lack a supply of cold gas. We find that 84 per cent of our sample release more than 10 per cent of their accretion power in their jets, showing that mechanical AGN feedback is significantly underestimated in many hydrodynamical simulations. There is a scatter of ~2 dex in the fraction of the accreted AGN power deposited back into the ISM in mechanical form, showing that the assumption in many simulations that there is a direct scaling between accretion rate and radio-mode feedback does not necessarily hold. We also find that mechanical feedback is significant for many of the HERGs in our sample as well as the LERGs.I will also discuss the influence of environment on the accretion rates and host galaxy properties of the radio sources in this sample. Finally, I will discuss plans to build on this work using the MeerKAT telescope here in South Africa.
Obscuration properties of radio galaxies
Ricci, Claudio
Most of the accretion onto supermassive black holes happens during a phase in which the AGN is obscured. While the study of obscured AGN has been a hot topic of research over the past two decades, the physical mechanisms regulating the amount of material around these object is still debated. In a recent work (Ricci et al. 2017c, Nature 549, 488) we have shown that radiative feedback plays a dominating role in shaping the close environments of AGN; however, it is still unclear whether the powerful jets often observed in the radio could also contribute to decrease the level of obscuration, sweeping the material away.Our group has carried out the multi-wavelength study of a large sample of local AGN selected in the hard X-ray band, where obscuration does not play a strong role (Ricci et al. 2017d, ApJS 233, 17; Koss et al. 2017, ApJ 850, 74, see www.bass-survey.com). In my talk I will discuss the obscuration properties of the ~100 radio galaxies in our sample, and discuss the relation between jets and the close environments of AGN.
Search for faint high redshift radio galaxies at low frequencies
Saxena, Aayush
High-redshift radio galaxies (HzRGs) are progentors of the most massive elliptical galaxies we see today. HzRGs are often foung in overdense regions in the early universe (in the centres of clusters and protoclusters) and are seen to be forming stars intensively. Their bright radio luminosities coupled with strong emission line strengths make them a unique beacon to study the most massive galaxies across the universe. At redshifts z>6, into the epoch of reionisation, radio galaxies can be used as unique probes to study the evolution of the neutral fraction of the intergalactic medium through the redshifted 21cm absorption signals in their spectra. Detection of even a single HzRG at z>6 could have profound implications for comoslogy. In this talk, I will present results from our search for faint HzRGs at 150 MHz from the TGSS ADR survey. Our sample probes a unique parameter space in flux density and spectral index. We have shortlisted 32 promising candidates from over 600000 sources and have followed them up at optical and infrared wavelengths (Saxena et al. 2018). We have confirmed redshifts in the range 1.5 < z < 5.7, which includes the discovery of the most distant radio selected galaxy known to date, with a Lyman alpha redshift of z=5.72 (Saxena et al. in prep). This object is by far the brightest radio source close to the epoch of reionisation and helps extend studies of HzRGs to never-seen-before redshifts. For a radio galaxy to exist at this epoch, its central SMBH must have been accreting very actively in the early universe. Discovery of the most distant radio galaxy from a preliminary sample is promising news for HzRG searches to probe the epoch of reionisation in unparalleled detail with next generation telescopes such as LOFAR, which is predicted to detect hundreds of radio galaxies at z>6 (Saxena et al. 2017).
Radio AGN in LOFAR surveys -- large samples at last!
Hardcastle, Martin
The LOFAR Tier-1 survey of the Northern sky (LoTSS) is the first large-area survey to simultaneously have the long baselines to detect extended emission from radio-loud AGN and the resolution to identify them with host galaxies -- we can select, image and identify objects in a single survey -- and is ten times deeper than any existing large-area survey. As such it will provide samples larger by many orders of magnitude than what we have at present. I will present results from the first data release of LoTSS, including a robustly selected AGN sample, constraints on the local jet kinetic luminosity function and studies of rare subclasses of objects such as restarting sources and giants.
RadioAstron imaging of nearby radio galaxies
Savolainen, Tuomas
RadioAstron Nearby AGN Key Science Program uses the ultra high angular resolution provided by the space-VLBI mission RadioAstron to study the structure of the jets in nearby radio galaxies close to their formation site. Our space-VLBI images of 3C84 and M87 well resolve both jets in transverse direction, revealing structures that are not seen in the ground-based VLBI data. In 3C84, we are able to resolve the limb-brightened jet just 30 microarcseconds from the core in our 22GHz image, which allows us to measure the jet collimation profile from ~10^2 to ~10^4 gravitational radii from the black hole. We find a very broad, almost cylindrical structure extending all the way to the core. The bright outer layer has a transverse radius of 250 gravitational radii at only 350 gravitational radii (deprojected) from the core, which raises a possibility that the jet sheath originates in the accretion disk. Our 5GHz RadioAstron image of 3C84 shows a previously unseen low-intensity emission from a cocoon-like structure around the recently restarted, one parsec long, jet. The cocoon pressure may provide a natural explanation for the cylindrical jet profile seen in the 22GHz image. In the case of M87, we have obtained a high dynamic range image at 1.6GHz, which reveals a pattern of helical filaments inside the jet. The origin of this structure will be discussed.
Compact Symmetric Objects: the key to understanding the initial stages of a radio source expansion
Sobolewska, Malgosia
Relativistic outflows from AGN propagate out to hundreds of kpc distances from the origin and impact environment on many scales, and thus influence evolution of structures in the universe. Compact extragalactic radio sources provide important insights into the initial stages of a radio source evolution and probe states of black hole activity at the time of the formation of a relativistic outflow. These compact sources show radio features typically observed in large-scale radio galaxies (jets, lobes, hot spots), but contained within the central 1 kpc region of the host galaxy. Compact Symmetric Objects (CSOs, a subclass of GigaHertz Peaked spectrum radio sources) are not affected by beaming and their linear radio size can be translated into a source age if one measures the expansion velocity of the radio structures. Such ages have been measured for a small sample of CSOs. Using the Chandra X-ray Observatory, XMM-Newton and NuSTAR we observed a pilot sample of 16 CSOs in X-rays (6 for the first time). Our results show heterogeneous nature of the CSOs X-ray emission indicating a range of AGN luminosities and complex environments. In particular, we identified four X-ray sources obscured with a dense medium (equivalent column > 1023 cm-2) capable of disturbing/slowing down the jet and confining the jet to a small region. Thus, for the first time we gain the observational evidence in X-ray domain in favor of the hypothesis that in a sub-population of CSOs the radio jets may be confined by the dense X-ray obscuring medium. As a consequence, the kinematic ages of these CSOs may be underestimated. We discuss the implications of our results on the emission models of CSOs, the earliest stages of the radio source evolution, jet interactions with the ISM, diversity of the environments in which the jets expand, and jet-galaxy co-evolution.
AGN Feedback and its Importance to Galaxy Evolution in the Era of the Next Generation Very Large Array
Nyland, Kristina
Energetic feedback by Active Galactic Nuclei (AGNs) plays an important evolutionary role in the regulation of star formation (SF) on galactic scales. However, the effects of this feedback as a function of redshift and galaxy properties such as mass, environment and cold gas content remain poorly understood. The broad frequency coverage (1 to 116 GHz), high collecting area (about ten times higher than the current Karl G. Jansky Very Large Array), and superb angular resolution (maximum baselines of at least a few hundred km) of the proposed next generation Very Large Array (ngVLA) are uniquely poised to revolutionize our understanding of AGNs and their role in galaxy evolution. Here, we provide an overview of the science related to AGN feedback that will be possible in the ngVLA era and discuss exciting opportunities for multi-wavelength synergy with other next-generation instruments, such as the Square Kilometer Array and the James Webb Space Telescope. We also present ngVLA imaging simulations of resolved radio jets spanning a wide range of intrinsic extents. As supported by our simulations, the unique combination of high resolution, large collecting area, and wide frequency range of the ngVLA will enable significant advancements in our understanding of the effects of jet-driven feedback on sub-galactic scales, particularly for sources with extents of a few pc to a few kpc such as young and/or lower-power radio AGNs, AGNs hosted by low-mass galaxies, radio jets that are interacting strongly with the interstellar medium of the host galaxy, and AGNs at high redshift.
High-energy emission of jetted AGN
Schwartz, Daniel
Quasars with flat radio spectra and one-sided arc-second scale jets are found to have similar scale X-ray jets in about 60% of such objects, even in short 5 to 10 ks Chandra observations. Jet radio emission is synchrotron radiation, as known from its polarization. The X-ray emission is explained most simply, i.e. with the fewest additional parameters, as inverse Compton (iC) scattering of cosmic microwave background (cmb) photons by the relativistic electrons in the jet. With physics based assumptions, one can estimate enthalpy fluxes upwards of 10^46 erg per second, sufficient to reverse cooling flows in clusters of galaxies, and play a significant role in the feedback process which correlates the growth of black holes and their host galaxy bulges. On a quasar-by-quasar basis, we can show that the total energy to power these jets can be supplied by the rotational energy of black holes with spin parameters as low as a=0.3. For a few bright jets at redshifts less than 1, the Fermi gamma ray observatory shows upper limits below the fluxes predicted, calling the iC/cmb mechanism into question. At large redshifts, the cmb energy density is enhanced by a factor (1+z)^4, so that iC/cmb must be the dominant mechanism for relativistic jets unless their rest frame magnetic field strength is hundreds of micro-Gauss. A new Chandra survey for jets in radio quasars at z > 3 has revealed cases of X-ray jets and lobes extending beyond the detected radio emission.
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.