Focus Meeting 8 - Poster Abstracts


Faraday rotation signatures of fluctuation dynamos in young galaxies

Sur, Sharanya

Observations of Faraday rotation through high-redshift galaxies has revealed that they host coherent magnetic fields that are of comparable strengths to those observed in nearby galaxies. These fields could be generated by fluctuation dynamos. In this talk, we will report on the resulting rotation measure (RM) and the degree of coherence of such fields obtained from idealized numerical simulations of fluctuation dynamos in forced compressible turbulence up to rms Mach number of 2.4. We show that the rms values of RM at dynamo saturation is of the order of 45 - 55 per cent of the value expected in a model where fields are assumed to be coherent on the forcing scale of turbulence. The dominant contribution to the RM in subsonic and transonic cases comes from the general sea of volume filling fields, rather than from the rarer structures. However, in the supersonic case, strong field regions as well as moderately overdense regions contribute significantly to the RM. Our results are in agreement with the observed RMs in young galaxies.

Magnetic field constraints in the outskirts of galaxies

Lopez, Ericson

Based on CO(2-1) public data, we study the monoxide oxygen gas excitation conditions and the magnetic field strength of four spiral galaxies. For the galaxy outskirts, we found kinetic temperatures in the range of 35 - 38 K, CO column densities 10^15 - 10^16 cm^(-2), and H2 masses 4 x10^6 - 6 x 10^8 Ms. An H2 density 10^3 cm^(-3) is suitable to explain the 2 sigma upper limits of the CO(2-1) line intensity. We constrain the magnetic field strength for our sample of spiral galaxies and their outskirts by using their masses and H2 densities to evaluate a simplified magneto hydrodynamic equation. Our estimations provide values for the magnetic field strength in the order of 6-31 uG.

New results on the magnetic field in M31

Beck, Rainer

The magnetic field of M31 is very regular, preserving its direction along a ring-like structure in the disk. This is regarded as the first and best evidence so far for the action of a large-scale dynamo in spiral galaxies. The regular field leads to fast diffusion of cosmic rays and prevents the formation of a radio halo of detectable surface brightness. The magnetic field in the central region is inclined to the disk and of opposite direction, indication of a major merger event in the past. New Effelsberg surveys at 11.1, 6.2, and 3.6 cm allowed us to derive maps of synchrotron emission, magnetic field strengths, and Faraday rotation with improved resolution and accuracy. M31 became the cornerstone to investigate the nonthermal properties of spiral galaxies.

Turbulent Generation of Galaxy Cluster Magnetic Fields

Jones, Thomas

Observations, and especially radio observations, reveal that microGauss-strength magnetic fields commonly pervade ICMs. Although the bulk dynamical stresses of those fields are probably sub-dominant to other forces, the fields should still play critical roles in ICM behaviors through microphysics, energy transport and dissipation processes. Largely independent of the sources of ICM seed magnetic fields, the extent and magnitude of the fields almost certainly depend on amplification and distribution by ICM turbulence. The effectiveness of turbulence in this context depends, in turn, on the strength, distribution, duration and character of the turbulence during cluster formation and evolution. In this presentation I will outline results from our simulation studies of MHD turbulence and cluster formation dynamics addressing these issues. I will emphasize the importance of turbulence "character", as well as its distributions in space and time, and also stress the implications to ICM physics of the observed ICM magnetic field properties.This work is supported at the University of Minnesota by the US National Science Foundation and the University of Minnesota Supercomputing Institute.

Magnetic fields and CR propagation in the halo of spiral galaxies as deduced from the CHANG-ES survey

Krause, Marita

With CHANG-ES, a survey of 35 edge-on galaxies in radio continuum and polarization with the EVLA in C- and L-band, we now better understand the halos of spiral galaxies and their magnetic fields. In the halo we observed again in strong X-shaped (and vertical) magnetic fields in several galaxies. However, it was unknown whether these fields are regular (coherent) or anisotropic (e.g. elongated loops). We now detected for the first time a large-scale Faraday depth pattern with different signs, indicating the existence of regular (coherent) magnetic fields in the halo of spiral galaxies. The results for the well-known galaxy NGC 4631 are presented and discussed in more detail.Further, we determined and analyzed the radio scale heights in a CHANG-ES subsample of 13 galaxies in a coherent way. The results are:Galaxies with smaller scale lengths are more spherical in the radio emission, while those with larger scale lengths are flatter.The radio scale height depends mainly on the radio diameter of the galaxy.The sample galaxies are consistent with an escape-dominated radio halo with convective cosmic ray propagation, indicating that galactic winds are a widespread phenomenon in spiral galaxies.While a higher star formation rate or star formation surface density does not lead to a higher wind velocity, we found for the first time observational indication of a gravitational deceleration of CRE outflow, i.e. a lowering of the wind velocity from the galactic disk.

Jet production in black-hole X-ray binaries and AGN: mass feeding and advection of magnetic fields

Cao, Xinwu

Relativistic Jets are observed only in the low/hard and intermediate states of X-ray binaries (XRBs), and are switched off in the thermal state, but they appear to be present in both low-luminosity and luminous active galactic nuclei (AGNs). It is widely believed that strong large-scale magnetic fields is a crucial ingredient in jet production; such fields can be attained only through efficient advection from the outer disc. We suggest that geometrically thin accretion discs with magnetic outflows are present in luminous radio-loud AGNs; this is likely because the interstellar medium provides both mass and sufficient magnetic flux to the outer disc. Most angular momentum of such disc is removed by the outflows, and the radial velocity of the disc is significantly increased compared to viscous drift velocity. This facilitates efficient magnetic field advection through the disc to produce a strong field near the black hole in luminous AGNs, which helps launch relativistic jets. In XRBs, the magnetic fields of the gas from companion stars are too weak to drive outflows from outer discs. Jets are therefore switched off in the thermal state due to inefficient magnetic field advection in the disc.

Galactic winds in nearby galaxies traced with radio continuum observations

Heesen, Volker

Galactic winds driven by cosmic rays (CRs) have since long been suspected to be an important ingredient in the evolution of galaxies, however, they have been proven elusive to detect observationally. This is possibly now about to change with the advent of sensitive low-frequency observations such as with the Low-Frequency Array (LOFAR), allowing us to see CR electrons far away from star-formation sites. They can be combined with new broadband, high-frequency observations such as with the refurbished Very Large Array (VLA), in order to study spatially resolved radio continuum spectra at matched angular resolution and sensitivity. On the modelling side there has been progress as well, both with numerical 3D simulations incorporating CR transport as well as with 1D semi-analytical models of CR-driven winds and of pure CR advection and diffusion. Here, we present results from our survey of nearby late-type spiral edge-on galaxies using archival data from a wide range of radio interferometers and single-dish telescopes as well as new observations at 140-MHz with LOFAR and 1.5- and 6-GHz observations from the CHANG-ES (Continuum Halos in Nearby Galaxies – an EVLA Survey) survey to explore the vertical CR transport in radio haloes. Early results are promising, with two types of haloes emerging: either they can be described as diffusion dominated, with diffusion coefficients in fair agreement with the Milky Way value, or they are advection dominated, with advection speeds within a factor of two in agreement with the escape velocity near the galactic mid-plane. This raises the possibility that winds are common in star-forming galaxies; they are visible as radio haloes extending over the entire disc and are related to processes connected to star formation. More work needed to better understand the relationship between cosmic rays and magnetic fields with other halo constituents such as the warm neutral, warm ionised, and hot ionised medium.

Spatial and Temporal Correlations in the Interstellar Medium

Hollins, James

We apply correlation analysis to random fields in numerical simulations of thesupernova-driven interstellar medium (ISM) with the magnetic field produced bydynamo action, and compare the properties of simulated radio observables withthe physical components in the model.We consider the cold, warm, and hot phases of the ISM separately; theanalysis mostly considers the warm gas, which occupies the bulk of thedomain.The correlation scales of random magnetic field, density, and velocityare distinct at all heights in the warm phase.The correlation time of the random velocity is comparable to the eddy turnovertime, although it may be shorter in regions with a higher starformation rate.The random magnetic field is anisotropic, with the standard deviations ofthe $y$- and $z$-components enhanced compared to the standard deviationof the $x$-component.The anisotropy is attributed to the global velocity shear from galacticdifferential rotation, and locally inhomogeneous outflow to the galactichalo.The correlation length of Faraday depth along the is greater than thecorrelation lengths of both electron density and vertical magnetic field.Such comparisons may be sensitive to the orientation of the line of sight.Uncertainties of the structure functions of synchrotron intensity rapidlyincrease with the scale. This feature is hidden in power spectrumanalysis, which can undermine the usefulness of power spectra fordetailed studies of interstellar turbulence.

Reliable detection and characterization of low-frequency polarized sources in the LOFAR M51 field

Horellou, Cathy

The new generation of broad-band radio continuum surveys will provide large data sets with polarization information. New algorithms need to be developed to extract reliable catalogs of linearly polarized sources that can be used to characterize those sources and produce a dense rotation measure (RM) grid to probe magneto-ionized structures along the line of sight via Faraday rotation.We have developed a computationally efficient and rigorously defined source-finding algorithm for linearly polarized sources.We used the calibrated data set from the LOw Frequency ARray (LOFAR) at 150 MHz centered on the nearby galaxy M51 to search for polarized background sources. We cataloged about 3000 continuum sources within 2.5 degrees of the center of M51. We made Stokes Q and U images centred on each source brighter than 100 mJy in total intensity and used RM synthesis to create Faraday cubes. For each source, the noise distribution function was determined; the peaks in polarized intensity in the Faraday spectrum were identified and the p-value of each source was calculated. Finally, the False Discovery Rate method was applied to the list of p-values to produce a list of polarized sources and quantify the reliability of the detections.  Of the 201 sources that were searched for polarization, six polarized sources were detected confidently. This corresponds to a number density of one polarized source per 3.3 square degrees, or 0.3 source per square degree. Increasing the false discovery rate to 50 percent yields 19 sources. A majority of the sources have a morphology that is indicative of them being double-lobed radio galaxies, and the ones with literature redshift measurements have 0.5<z<1.0.we find="" that="" this="" method="" is="" effective="" in="" identifying="" polarized="" sources. in="" the="" future,="" we="" intend="" to="" develop="" it="" further="" and="" apply="" larger="" data="" sets="" such="" as="" lofar="" two-meter="" survey="" of="" whole="" northern="" sky,="" lotss,="" ongoing="" deep="" observations="" goods-north="" field.<="" p="">

Rotation measure asymmetry reveals a precession of the AGN outflow in a Seyfert galaxy.

Damas-Segovia, Ancor

Feedback on galactic-scales is an important question in studies of cosmic evolution of galaxies. It is believed that AGN driven jets and/or stellar winds plays an important role in driving materials away from galactic discs. In this regard, we demonstrate that radio polarization studies of galactic outflows can help to distinguish between various driving mechanisms. New broad band polarimetric observations from the CHANG-ES project of the galaxy NGC 4388 with the JVLA showed extended features in the radio polarized intensity of this Virgo galaxy. In this work we show how a jet precession model can well explain the complexity of these nuclear outflows and allows us to infer physical parameters of this ejection like velocity, inclination, period, and total time of ejection. For the first time, the direction of the outflow with respect to the line of sight is introduced into this model and compared to the observed rotation measures (RMs) of the nuclear outflow, showing good agreement between the modeled RMs and the polarization radio observations. Furthermore, this precession model, combined with polarimetric radio observations, could serve as a tool for studying the interaction of nuclear outflows with their environments.

Generalized Faraday rotation of the CMB polarized anisotropies by large scale structures

Lemarchand, Nadège

A cluster of galaxies is both a magnetized relativistic and non relativistic plasma. Thus, it acts as a birefringent medium for the light that goes through this kind of structures. In particular, CMB photons cross clusters of galaxies on their way to us. Depending on the relativistic nature or not of the free electrons in the plasma, the effect on the CMB polarization will be different. In the case of a cold plasma, the polarization plane is rotated after going through a cluster of galaxies (Faraday Rotation). On the contrary, when the plasma is relativistic, CMB photons experience Faraday Conversion which transfers linear polarization into circular polarization. I looked at a statistical study of this effect, by first focusing on predicting the angular power spectra of such effects due to clusters, using a line-of-sight approach and the halo model, implementing the cosmological principle for the statistics of the directions of the magnetic fields inside clusters. These effects are both sensitive to the cosmology through the mass function of the clusters and so parameters such as s8, and to the distribution of the magnetic field and electrons inside a cluster, and can be used as a probe both for cosmology and for clusters of galaxies. Then I looked at the consequences of these effects on the angular power spectra of the CMB polarized anisotropies: the Faraday rotation effect mixes the E and B modes (creating secondary B modes in addition to the primordial and lensing ones), whereas the Faraday conversion effect transfers E and B anisotropies into the V mode, creating circular polarization which has no primordial origin in the standard cosmological scenario. Finally, I will sketch how polarized CMB anisotropies can be used for reconstructing the Faraday rotation and conversion fields.

Magnetic field effects on the ISM structure and galactic outflows

Shukurov, Anvar

We explore the effect of magnetic fields on the vertical distribution, multiphase structure and outflow of the gas and turbulence in simulations of interstellar medium (ISM) driven by supernova (SN) explosions. Magnetic field makes the ISM more homogeneous and reduces the fractional volume occupied by the hot phase. Magnetic pressure generally weakens systematic gas flow away from the mid-plane. Magnetic field strength is maximum at about the height |z| = 0.3 kpc above the mid-plane,  and magnetic pressure gradient counteracts the outflow at the smaller heights and facilitates it above. The downward magnetic pressure gradient at |z| < 0.3 kpc leads to an almost uniform gas  distribution along z near the mid-plane. The role of magnetic tension is weaker at the base of the halo than often assumed. Remarkably, an imposed magnetic field affects the ISM structure differently from a large-scale field generated self-consistently by the dynamo action: the dynamo magnetic field evolves together with the ISM and its effects on the gas are more diverse and subtle than those of an imposed magnetic field.

Particles Acceleration in the Kilonovae Shock

Wang, Xin

Cosmic ray generally can be accelerated by the astrophysical shock,e.g. for SNR or AGN. The cosmic ray energy spectrum with its largeenergy range from GeV to ZeV (~1021eV). Generally, the energyspectrum below "knee" (3.5X1015eV) can be accelerated by thegalactic origins. But the energy spectrum beyond "knee" could beoriginated from the extragalactic Universe, this part remain poorlyunderstood. Magnetic field and the amplification in theastrophysical burst will play important role on the particlesacceleration at the astrophysical shocks. However, there is scarcelytheoretical model can directly verify the astrophysical magneticfield in galactic origins accelerate the particle energies to the "knee" energy range. In this work, we perform a simulation tocalculate the particles acceleration processes at the kilonovaeshock. We suggest that the kilonova environment driven a shock couldaccelerate the particles to the energy spectral "knee" with theiramplification of the magnetic turbulence.

The evolution of large scale magnetic fields in spiral galaxies

Rodrigues, Luiz Felippe Santiago

We investigate how the large scale magnetic fields in the discs of spiral galaxies evolve through cosmic time. To do this, we couple the galaxy properties computed by a semi-analytic model of galaxy formation to the mean field dynamo equations. These are solved numerically as a function of time and galactocentric radius for a thin disc using the no-z approximation, with imposed axial symmetry, and the dynamical quenching non-linearity. A simple prescription for the evolution of the random (small-scale) magnetic field component and its relation with the mean (large-scale) component is adopted. This allows us to compute radial and time dependent properties of the interstellar medium of discs for a statistical sample of galaxies from z~7 until the present. We compute the distribution of the typical magnetic field strength at different redshifts and the dependence of these on galaxy mass. We examine the evolution of the growth rate of the mean disc magnetic fields of galaxies and discuss the steady state assumption. Finally, we analyse what is the sensitivity of our results to specific assumptions and to the galaxy formation model.

Polarization as a Probe of Thick Dust Disk in Edge-on Galaxies: Application to NGC 891

Seon, Kwang-il

Radiative transfer models were developed to understand the optical polarizations in edge-on galaxies, which are observed to occur even outside the geometrically thin dust disk, with a scale height of ˜ 0.2 kpc. In order to reproduce the vertically extended polarization structure, we find it is essential to include a geometrically thick dust layer in the radiative transfer model, in addition to the commonly-known thin dust layer. The models include polarizations due to both dust scattering and dichroic extinction which is responsible for the observed interstellar polarization in the Milky Way. It is found that the magnetic fields in edge-on galaxies are in general vertical (or poloidal) except the central part, where the magnetic fields are mainly toroidal or have no coherent pattern. We also find that the polarization level is enhanced if the clumpiness of the interstellar medium, and the dichroic extinction by vertical magnetic fields in the outer regions of the dust lane are included in the radiative transfer model. The predicted degree of polarization outside the dust lane was found to be consistent with that (ranging from 1% to 4%) observed in NGC 891.

Far-infrared polarization of galaxies with SOFIA/HAWC+

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 emission and distribution of dust in galaxies as well as the morphology of their magnetic fields. However, the atmosphere is opaque to the 50-220 µm range and observations are impossible from ground-based telescopes. Furthermore, polarimetric capabilities have been very limited in this wavelength range. HAWC+ has opened a new window to explore active galactic nuclei (AGN) and starburst galaxies, providing the best angular resolution within the 40-300 µm range of the current suite of instruments.We here present the results of a massive spiral galaxy containing an AGN, NGC 1068, and a starburst galaxy, M82, observed at 53 µm and 89 µm with the far-IR (FIR) polarimeter HAWC+ onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). Specifically, our polarization observations of NGC 1068 at 53 µm have shown for the first time a magnetized arm along the spiral inner arms of the galaxy. Our polarized flux observations of M82, in combination with previously published NIR polarimetric observations, have shown evidences of a galactic magnetic wind at scales of several hundred parsecs.

ALMA polarization studies of Nearby galaxies

Paladino, Rosita

Magnetic fields are an essential ingredient of star formation in galaxies, at various spatial scales.They affect directly the mean gas density, which impacts significantly the star formation rate, but they also regulate the collapse and fragmentation of molecular clouds.Nearby galaxies offer the unique opportunity to study magnetic fields in different environments on large scales, while still being close enough to allow detailed studies of small scale structures.The large scale magnetic fields in galaxies are investigated through observations of synchrotron polarized emission. On giant molecular clouds scales, so far only in the Milky Way, dust polarization measurements have been obtained. Relating these different tracers at different scales is fundamentalto clearly understand the role of magnetic fields.With current data for the Milky Way, it is difficult to reconcile magnetic field models with both synchrotron and dust polarization observed. More sophysticated models are needed, and observational constraints on the observed dust polarization in different location of nearby galaxies are crucial.ALMA, with its incomparable combination of resolution and sensitivity, offers a new tool to observe dust continuum at GMC scales in nearby galaxies and detect its polarization.With these unprecedented observations it will be possible to combine dust polarization and synchrotron information to build a coherent picture of magnetic fields in galactic interstellar medium.

Inflow-Outflow in the magnetosphere of a black hole

Chantry, Loic

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. The geometry of the self-similar solutions is not fixed in advance and is determined by transversal forces balance. These models takes into account the light cylinder effects.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 and magnetic flux of the ultra-relativistic outflow solutions are of the same order as those 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 energetic 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. We discuss an ensemble of inflow solutions, emphasing features and topology for the magnetic field in the vicinity of the black hole.

Magneto-thermo-turbulent star formation in cosmic zoom-in spiral galaxies

Martin-Alvarez, Sergio

An incredibly successful and simple description of star formation on galactic scales is the Kennicutt-Schmidt law which relates the star formation rate to gas density. At smaller scales however, complex local dynamical processes driven by phenomenon such as stellar feedback, turbulence and/or magnetic fields are thought to be necessary to explain star formation.As numerical simulations are able to resolve unprecedented spatial scales, sub-grid prescriptions need to be adapted to consistently model those physical processes that still remain below the resolution limit. By means of a suite of constrained transport magnetohydrodynamical adaptive mesh refinement high-resolution cosmological zoom-in simulations of Milky Way-like spiral galaxies, we explore how modelling star formation through a local magneto-thermo-turbulent prescription affects the properties of the resulting galaxies. We focus specifically on the role played by magnetism. We find that for most levels of magnetisation, even though the presence of magnetic fields considerably modifies star formation histories, it does not substantially alter the resulting stellar mass. Only at the strongest magnetisations tested, is the stellar mass halved. We also explore how stellar feedback changes the effect of magnetic fields and hence star formation.

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.

CHANG-ES - an overview

Stil, Jeroen

CHANG-ES (Continuum Halos in Nearby Galaxies - and EVLA Survey) is a survey of 35 nearby edge-on galaxies with the JVLA in L band (B, C, and D configuration) and C band (C and D configuration) in all four Stokes parameters. Science goals include the origin of radio halos in galaxies, magnetic fields at the interface between disks and halos, cosmic ray transport, the far-infrared-radio correlation, and large-scale magnetic field structure in the halos of galaxies. On this poster we introduce the survey on behalf of the CHANG-ES team, and present a selection of results from the survey so far.

The CHANG-ES view of NGC 4666

Dettmar, Ralf-Juergen

We present CHANG-ES VLA data of the nearby superwind and starburst edge-on spiral galaxy NGC 4666, which is a member of a small group of galaxies in a distance of 27.5 Mpc. The observations were carried out at two different radio frequencies (1.5 GHz and 6 GHz) and with all polarization products. With these data the magnetic field strength as well as the magnetic field configuration in the halo and the disk is investigated. Further analysis of the rotation measure (RM) values along the disk of the galaxy (from RM-synthesis) reveals reversing magnetic fields within the magnetized disk. To our knowledg this is the first report of a field reversal in the disk of an external galaxy.

Magnetic fields at the epoch of reionization

Battaner, Eduardo

We detected magnetic fields with strengths of the order of 10-8 G at the epoch of Reionization. These were identified by using CMB data to obtain Faraday Rotation at both, the map and the spectrum level. The multipole region of about l<12 and the lack of correlations with either, galactic emissions (Faraday rotation, synchrotron and dust) or with CMB anisotropies and lensing, support our identification.

Variability of magnetically-dominated jets in blazars and gamma ray bursts

Agnieszka, Janiuk

The fastly variable accretion flows are found in a number of different types of astrophysical black hole sources. At largest scales, they are present in the cores of active galaxies.In the radio-loud objects, such as blazars, the variability of the inflow can be transmitted to the outflow properties. In these sources,the relativistic jets are pointing to our line of sight.In addition, many similarities are found between the jet physics in blazars and in gamma ray bursts.The latter are observed from extragalactic distances, butoperate at smaller scales, within the stellar-mass accreting black holes and in collapsing star's environment.Observational studies have shown an anticorrelation between minimum variability time scale and Lorentz factor of the emitted jet.Motivated by those observational properties of black hole sources, we investigate the accretion inflow and outflow properties,by means of numerical GRMHD simulations.Our two-dimensional magneto-hydrodynamical models are computed in full General Relativity, implemented with the code HARM. The properties ofmagnetic fields and their role in evolution in the flows are studied in detail.The blazar jet is Poynting-dominated, and powered by the Blandford-Znajek mechanism which can extract energy from a rotating black hole. This mechanism is nowwell known and tested in the purpose of a jet launching, but observations are showing variability in the jet emission. Multiple shocks that collide in the jet,can lead to multiple emission episodes and can account for the fluctuating light curve. A reasonable interpretation of this effect is that the variabilityobserved in the jets can directly reflect the central engine variability. The latter is tightly related to the action of magnetic fields in the center of thegalaxy.

Spectral analysis of the magnetic field evolution in the ICM

Dominguez-Fernandez, Paola

The origin of the observed magnetic fields in the intracluster medium remains to be unclear.  Nevertheless, there are two plausible scenarios that can be able to explain the corresponding radio observations: a primordial scenario where magnetic fields were generated in the very early Universe during phase-transitions, or an astrophysical scenario were magnetic fields were generated by starbursts or AGNs and later on spread into the ICM. Supporting the first scenario, we study the evolution of magnetic fields in a major merger scenario coming from a cosmological MHD simulation made with ENZO (The ENZO collaboration et al. 2013) where the initial magnetic field seed gets amplified via a turbulent dynamo during structure formation. Since this is the first cosmological  simulation of the ICM that resolves the magnetic dynamo action (Vazza et al. 2018), we are able to make an analysis of the magnetic power spectra following closely the dynamo theory predicted first by Kazantzev's theory (Kanzantzev 1967).

Magnetized stars embedded in AGN accretion disks and tori

Zajacek, Michal

A population of magnetized stars (neutron stars, white dwarfs, young T Tauri stars, and chemically peculiar Ap and Bp stars) is expected to be embedded within an accretion disk or a torus near a supermassive black hole (SMBH) in active galactic nuclei (AGN). The dipole-type magnetic field can significantly influence the gaseous environment within the region of influence around the star, depending on the intrinsic strength of its dipole and parameters of the surrounding medium. We estimate the fraction of the volume in the accretion disk/torus where the structure must be entirely changed by the presence of the embedded magnetized stars, as compared with an unperturbed solution.

An idea for a SOFIA nearby galaxies far-IR legacy survey

Zinnecker, Hans

In this poster, we propose a combined large (~100 hr)continuum and line emission far-IR legacy survey of nearby star forming galaxies with the SOFIA air-borne NASA/DLR Observatory (2.5m telescope), using the far-IR camera HAWC+ and far-IR integral fieldspectrometer FIFI-LS, with a FOV of 1' or more(in the case of HAWC+).We first select a distance-limited sample of 50-100 nearbystar forming galaxies (10-40Mpc), each of which fit intothe FOV and are, for scheduling, conveniently distributed all over the sky.We will study the spatial distribution of far-IRdust emission at several HAWC+ far-IR wavelengths (53, 89, 154, 214 micron) and will measure their total far-infrared luminosities (a proxy fortheir total star formation rates). In addition,we will also map, with HAWC+, the multi-wavelength (53 and 89 micron) spatial distributionof polarized dust emission due to aligned dust grains,allowing us to infer the large-scale orientation ofmagnetic fields in these galaxies at 5-10" spatial resolution.(Herschel could not do this, as neither PACS nor SPIRE hada polarimetric mode).In the second part of this proposal, we will use FIFI_LSto measure the integral flux of the most important 158 micron [CII]ISM gas cooling line of these same star forming galaxies.We can then deduce the far-IR line-to-continuum luminosityratio of L_[CII]/L_FIR and can check to what extent is itindeed universal (of the order of 1%). This in turn is atest of the hypothesis that the [CII] luminosity is agood reliable star formation rate indicator, as is widely(but blindly) assumed in the high-z star formation community.Such an investigation of the "local truth" would seem to behighly desirable before accepting far-reaching extrapolationsof early universe star formation rates based on the detection ofhigh-redshifted [CII] emission with submm telescopes(e.g. with ALMA and NOEMA).We invite interested far-IR/submm astronomers to join and helpwith this SOFIA legacy proposal (new deadline: 7 Sept 2018).

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