AGN Cores Research Articles

High-Redshift Quasars at z ≥ 3: Radio Variability and MPS/GPS Candidates

We present a study of the radio variability of bright, S1.4≥100 mJy, high-redshift quasars at z≥3 on timescales of up to 30–40 yrs. The study involved simultaneous RATAN-600 measurements at the frequencies of 2.3, 4.7, 8.2, 11.2, and 22.3 GHz in 2017–2020. In addition, data from the literature were used. We have found that the variability index, VS, which quantifies the normalized difference between the maximum and minimum flux density while accounting for measurement uncertainties, ranges from 0.02 to 0.96 for the quasars. Approximately half of the objects in the sample exhibit a variability index within the range from 0.25 to 0.50, which is comparable to that observed in blazars at lower redshifts. The distribution of VS at 22.3 GHz is significantly different from that at 2.3–11.2 GHz, which may be attributed to the fact that a compact AGN core dominates at the source’s rest frame frequencies greater than 45 GHz, leading to higher variability indices obtained at 22.3 GHz (the VS distribution peaks around 0.4) compared to the lower frequencies (the VS distribution at 2.3 and 4.7 GHz peaks around 0.1–0.2). Several source groups with distinctive variability characteristics were found using the cluster analysis of quasars. We propose seven new candidates for gigahertz-peaked spectrum (GPS) sources and five new megahertz-peaked spectrum (MPS) sources based on their spectrum shape and variability features. Only 6 out of the 23 sources previously reported as GPS demonstrate a low variability level typical of classical GPS sources (VS<0.25) at 4.7–22.3 GHz. When excluding the highly variable peaked-spectrum blazars, we expect no more than 20% of the sources in the sample to be GPS candidates and no more than 10% to be MPS candidates.

Identification of the optical emission detected by Gaia with radio structures in parsec-scale active galactic nucleus jets

Aims. We investigated the location of the optical emission with respect to the parsec-scale radio structure and attempted to identify whether the optical centroid is coincident with the radio core or a radio component of the jet. Methods. We used optical Gaia DR3 and 8 GHz ICRF3 positions and a model fitting of 15 GHz imaging by the MOJAVE VLBA survey for 422 sources, mostly blazars. We searched for possible associations between optical centroids and radio components. We also compared the astrometric and photometric properties of each category, looked for trends between the various source parameters, and discussed possible biases. Results. Sources can be separated into four categories based on whether their optical centroid (i) falls onto the radio core (category C), (ii) lies close to the base of the jet (category B), (iii) coincides with a radio component downstream in the jet (category J), or (iv) is not found to coincide with a detected radio component (category O). Due to a number of random and systematic errors, the number of sources falling into each category remains approximate but close to 32%, 36%, 22%, and 10%, respectively. The family of quasars, mostly flat spectrum radio quasars (FSRQs), clearly dominates the C and B categories, with their percentage decreasing from categories C to O. Conversely, the family of BL Lacs is spread over the four classes and dominates the category O. Radio galaxies are mainly in classes O and J, and the radio-loud narrow-line Seyfert 1 all belong to class C. An individual analysis of O sources shows that, despite the absence of a direct association with a specific radio component, the optical Gaia centroid is globally related to the radio VLBI jet structure. Conclusions. Our study shows that the spatial distribution of the optical counterparts seen by Gaia below the 0.2-arcsec scale around the radio cores appears in the vast majority of cases to be related to the AGN core or to its jet, with most of them located downstream in the jet. Those associated to the core also exhibit a bluer color index, suggesting a possible contribution of the accretion disk to the optical emission, while those associated to a radio knot in the jet appear redder and tend on average to be found in more polarized radio sources. Most BL Lacs have their optical emission coincident with the jet base or a knot in the jet, while sources with an optical emission on or close to the radio core are mostly FSRQs. Radio components associated with the optical centroid at the jet base or along the jet are mainly stationary or quasi-stationary features, with low apparent MOJAVE velocities. There are indications that the apparent proper motion of the Gaia centroids may be higher than the speed of the associated radio components, but the significance of this trend requires further investigation.

The VLBA CANDELS GOODS-North Survey. II – Wide-field source catalogue comparison between the VLBA, EVN, e-MERLIN, and VLA

ABSTRACT Deep radio surveys of extragalactic legacy fields trace a large range of spatial and brightness temperature sensitivity scales, and therefore have differing biases to radio-emitting physical components within galaxies. This is particularly true of radio surveys performed at $\lesssim 1 \ \mathrm{arcsec}$ angular resolutions, and so robust comparisons are necessary to better understand the biases present in each survey. We present a multiresolution and multiwavelength analysis of the sources detected in a new Very Long Baseline Array (VLBA) survey of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey Great Observatories Origins Deep Survey-North field. For the 24 VLBA-selected sources described in Paper I, we augment the VLBA data with EVN data, and ∼0.1–1 arcsec angular resolution data provided by Very Large Array (VLA) and enhanced-Multi Element Remotely Linked Interferometry Network. This sample includes new active galactic nuclei (AGN) detected in this field, thanks to a new source extraction technique that adopts priors from ancillary multiwavelength data. The high brightness temperatures of these sources (TB ≳ 106 K) confirm AGN cores, that would often be missed or ambiguous in lower-resolution radio data of the same sources. Furthermore, only 15 sources are identified as ‘radiative’ AGN based on available X-ray and infrared constraints. By combining VLA and VLBA measurements, we find evidence that the majority of the extended radio emission is also AGN dominated, with only three sources with evidence for extended potentially star formation-dominated radio emission. We demonstrate the importance of wide-field multiresolution (arcsecond–milliarcsecond) coverage of the faint radio source population, for a complete picture of the multiscale processes within these galaxies.

A two-zone model as origin of hard TeV spectrum in extreme BL lacs

ABSTRACT The emission of the so-called extreme BL Lacs poses challenges to the particle acceleration models. The hardness of their spectrum, ≲ 2, in the high-energy band demands unusual parameters using the standard one-zone synchrotron self-Compton (SSC) model with a deficient magnetized plasma. Some authors use either two-zone or hadronic/lepto-hadronic models to relax these atypical values. In this work, we present a lepto-hadronic two-zone model to explain the multi-wavelength observations of the six best-known extreme BL Lacs. The very-high-energy gamma-ray observations are described by the photo-hadronic processes in a blob close to the AGN core and by SSC and external inverse Compton-processes in an outer blob. The photo-hadronic interactions occur when accelerated protons in the inner blob interact with annihilation line photons from a sub-relativistic pair plasma. The X-ray observations are described by synchrotron radiation from the outer blob. The parameter values found from the description of the spectral energy distribution for each object with our phenomenological model are similar to each other, and lie in the typical range reported in BL Lacs.

Theoretical investigation of Agn@(ZnS)42(n=6-16) using first principles: Structural, electronic and optical properties

Ag@ZnS nanoparticles display enhanced photocatalytic efficiency and good photoelectric properties compared to their single-component counterparts in the process of forming a core-shell structure using an Ag cluster as the inner core of a ZnS outer shell. In this study, first-principles calculations were used to investigate the structural, electronic, and optical properties of Agn@(ZnS)42 (n = 6-16) core-shell nanocomposites. The calculated results show significant even-odd oscillations in the structural stability, that is, Ag@ZnS nanostructures with an even number of Agn core atoms are relatively more stable than those with an odd number of core atoms. The second-order differences in the total energies (Δ2E) and the core-shell interaction energy Ecs indicate that a Ag12@(ZnS)42 nanostructure is the most stable configuration. A significant red shift was found in Agn@(ZnS)42 nanoparticles in the absorption spectrum compared with a (ZnS)48 nanostructure, which is likely attributed to the strong electron interactions between the Ag core and the ZnS shell.

Embedded AGN and star formation in the central 80 pc of IC 3639

Aims. Our goal is to probe the inner structure and the nature of the mid-IR emission in the active galaxy IC 3639, which hosts a Seyfert 2 nucleus and shows signatures of strong star-forming activity. Methods. We used interferometric observations in the N-band with VLTI/MIDI to resolve the mid-IR emission of this nucleus. The origin of the nuclear infrared emission is determined from: (1) the comparison of the correlated fluxes from VLTI/MIDI with the fluxes measured at subarcsecond resolution (VLT/VISIR, VLT/ISAAC); (2) diagnostics based on IR fine-structure line ratios, the IR continuum emission, IR bands produced by polycyclic aromatic hydrocarbons (PAH) and silicates; and (3) the high-angular resolution spectral energy distribution. Results. A large fraction of the total mid-IR emission of IC 3639 is produced in the innermost ≲80 pc with only ~1% of the total luminosity released in the UV/optical range. The unresolved flux of IC 3639 is 90 ± 20 mJy at 10.5 μm, measured with three different baselines in VLTI (UT1–UT2, UT3–UT4, and UT2–UT3; 46–58 m), making this the faintest measurement so far achieved with mid-IR interferometry. The correlated flux is a factor of 3–4 times fainter than the VLT/VISIR total flux measurement. The observations suggest that most of the mid-IR emission has its origin on spatial scales between 10 and 80 pc (40–340 mas). The emission confined within the inner 80 pc is either dominated by a starburst component or by the AGN core. The brightness distribution could be reproduced by a single component associated with the AGN, although this scenario would imply a very extended dust distribution when compared to other nearby Seyfert galaxies detected with MIDI. The extended component could also be associated with polar dust emission, that is, with a dusty wind blown by the AGN. However, a mixed contribution dominated by the star formation component over the AGN is favoured by the diagnostics based on ratios of IR fine-structure emission lines, the shape of the IR continuum, and the PAH and silicate bands. Conclusions. A composite AGN-starburst scenario is able to explain both the mid-IR brightness distribution and the IR spectral properties observed in the nucleus of IC 3639. The nuclear starburst would dominate the mid-IR emission and the ionisation of low-excitation lines (e.g. [Ne II]12.8 μm) with a net contribution of ~70%. The AGN accounts for the remaining ~30% of the mid-IR flux, ascribed to the unresolved component in the MIDI observations, and the ionisation of high-excitation lines (e.g. [Ne V]14.3 μm and [O Iv]25.9 μm).

Using Cross Entropy Optimization to Model Active Galactic Nuclei Light Curves from VLBA MOJAVE Images

Abstract We present in this article a new method to derive the observed properties of outbursts in relativistic jets. We use the VLBI MOJAVE maps to obtain the light curves, based on the principle that the variability of extragalactic sources, in this case 3C 279 and 4C +29.45, should appear in high resolution observations since 1996 until 2016. The use of the cross entropy method (CE) can accurately determine the ranges of parameters for a sequence of outbursts based on the shock-wave model, where the decay/rise timescale ratio has a small spread and the use of a unique index 1.3 generates a good fit modeled by functions of outbursts and by the model of the three stages. By the CE method, one can automatically get the start epochs as well as the occurrence of rise and decline times of the outbursts in the light curves. The values found are in agreement with the power-law distribution of energy, which shows that the cooling of electrons is a predominant process during the initial phase of the shock model evolution. The results of the decomposition show that the outbursts match the VLBI components observed in jets in addition to showing strong evidence of the peaks in the frequencies of 15.3 GHz. With this, we can model the shock waves with reference to the distance at the core of AGN to obtain the Doppler factor and the Lorentz factor.

Optical/Infrared Polarised Emission in X-ray Binaries

Recently, evidence for synchrotron emission in both black hole and neutron star X-ray binaries has been mounting, from optical/infrared spectral, polarimetric, and fast timing signatures. The synchrotron emission of jets can be highly linearly polarised, depending on the configuration of the magnetic field. Optical and infrared (OIR) polarimetric observations of X-ray binaries are presented in this brief review. The OIR polarimetric signature of relativistic jets is detected at levels of ~ 1-10 %, similar to AGN cores. This reveals that the magnetic geometry in the compact jets may be similar for supermassive and stellar-mass BHs. The magnetic fields near the jet base in most of these systems appear to be turbulent, variable and on average, aligned with the jet axis, although there are some exceptions. These measurements probe the physical conditions in the accretion (out)flow and demonstrate a new way of connecting inflow and outflow, using both rapid timing and polarisation. Variations in polarisation could be due to rapid changes of the ordering of the magnetic field in the emitting region, or in one case, flares from individual ejections or collisions between ejecta. It is predicted that in some cases, variable levels of X-ray polarisation from synchrotron emission originating in jets will be detected from accreting Galactic black holes with upcoming spaceborne X-ray polarimeters.

Multi-wavelength campaign on NGC 7469

Outflows in active galaxies (AGNs) are common, although their launching mechanism, location, and physical impact on the host galaxy remain controversial. We conducted a multiwavelength six-month campaign to observe the nearby Seyfert galaxy NGC 7469 with several observatories in order to better understand and quantify the outflow in this AGN. We report on the time-integrated line-resolved X-ray spectrum of NGC 7469 obtained with the Reflection Grating Spectrometer (RGS) on board XMM-Newton. We use the RGS spectrum to discern the many AGN outflow components. A global fit is applied to obtain their physical parameters. We find that the AGN wind can be well described by three narrow velocity components at -650, -950, and -2050 km/s. The RGS clearly resolves the -20 50 km/s component in C5+ Ly$\alpha$, while the -650 km/s and -950 km/s velocities are blended. Similar velocities are resolved in the UV. The H-equivalent column densities of these components are, respectively, NH = 7x10^20, 2.2x10^21, and 10^20 cm^-2, for a total of 3x10^21 cm^-2. The -650 km/s component shows a broad ionisation distribution. We identify a photo-ionised emission component blue-shifted by -450 km/s which we ascribe to the same outflow that produces the absorption lines. The elemental abundance ratios of C, N, Ne, S, and Fe to O in the outflow tend to be between 1 - 2 times solar. Preliminary estimates of the absorber distance from the AGN center suggest it is at least a few pc away from the center, but more advanced methods need to be applied in order to obtain better constraints. The complex X-ray spectrum of NGC 7469 demonstrates the richness of high energy phenomena taking place in AGN cores. The subtle spectroscopic differences between the various components require deep, high-resolution observations, such as the present RGS spectrum, if one is to resolve them and perform quantitative plasma diagnostics.

On the origin of two unidentified radio/X-ray sources discovered withXMM-Newton

We aim at clarifying the nature of the emission of two spatially related unidentified X-ray sources detected with XMM-Newton telescope at intermediate-low Galactic latitude. Observations reveal a point-like source aligned with elongated diffuse emission. The X-ray spectra are best-fitted by absorbed power laws with photon indices ~1.7 for the point-like and ~2.0 for the extended one. Both sources show nonthermal radio-continuum counterparts that might indicate a physical association. From the available data, we did not detect variability on the point-like source in several timescales. Two possible scenarios are analyzed: first, based on HI line absorption, assuming a Galactic origin, we infer a distance upper bound of <2 kpc, which poses a constraint on the height over the Galactic plane of <200 pc and on the linear size of the system of <2.3 pc. In this case, the X-ray luminosities are >10^32 erg/s and >7.5 x 10^32 erg/s, for the point-like and extended sources, respectively; second, an extra-Galactic nature is discussed, where the point-like source might be the core of a radio galaxy and the extended source its lobe. In this case, we compare derived fluxes, spectral indices, and spatial correlation with those typical from the radio galaxy population, showing the feasibility of this alternative astrophysical scenario. From the available observational evidence, we suggest that the most promising scenario to explain the nature of these sources is a system consisting of a one-sided radio galaxy, where the point-like source is an active galactic nucleus and the extended source corresponds to the emission from its lobe. Other possibilities include a PSR/PWN origin, where the radio/X-ray emission originates from the synchrotron cooling of relativistic particles in the PSR magnetic field or a casual alignment between two unrelated sources, such as an AGN core and a Galactic X-ray blob.

High-energy emission processes in M87

We study the contribution of thermal and non-thermal processes to the inverse Compton emission of the radio galaxy M 87 by modelling its broad-band emission. Through this we aim to derive insight into where within the AGN the X-ray, gamma-ray, and VHE emission is produced. We have analysed all available INTEGRAL IBIS/ISGRI data on M 87, spanning almost 10 years, to set an upper limit to the average hard X-ray flux of $f(20 - 60 \rm \, keV) < 3\times 10^{-12}$ $\rm \, erg \, cm^{-2} \, s^{-1}$, using several techniques beyond the standard analysis which are also presented here. We also analysed hard X-ray data from Suzaku/PIN taken late November 2006, and we report the first hard X-ray detection of M 87 with a flux of $f(20 - 60 \rm \, keV) = 10^{-11}\rm \, erg \, cm^{-2} \, s^{-1} $. In addition we analyse data from Fermi/LAT, INTEGRAL/JEM-X, and Suzaku/XIS. We collected historical radio/IR/optical and VHE data and combined them with the X-ray and gamma-ray data, to create broad-band spectral energy distributions for the average low-flux state and the flaring state. The resulting spectral energy distributions are modelled by applying a single-zone SSC model with a jet angle of theta = 15 degrees. We also show that modelling the core emission of M 87 using a single-zone synchrotron self-Compton model does represent the SED, suggesting that the core emission is dominated by a BL Lac type AGN core. Using SED modelling we also show that the hard X-ray emission detected in 2006 is likely due to a flare of the jet knot HST-1, rather than being related to the core.

Very Long Baseline Interferometry observations: the closest look at the cores of AGN

AbstractVery Long Baseline Interferometry (VLBI) provides the highest angular resolution achievable in astronomy, reaching sub-milliarcsecond scales. For radio loud AGNs, this offers the unique opportunity to directly image and monitor the fine details of the jet structure, approaching the event horizon in the nearest and most supermassive black holes, like in M87. After a quick review of various VLBI facilities, we present results from recent VLBI monitoring projects on two remarkable radio and high energy sources: the radio galaxy M87 and the BL Lac object Mrk421. For the latter, we present a detailed analysis of the jet structure in total intensity and polarization through the whole 2011, during which a multi-wavelength campaign took place. We reveal flux density variability but no significant changes in the jet structure. In M87, we detect and follow the evolution of the core and of the jet feature HST-1; we reveal superluminal motion of components within HST-1, with a possible connection between ejection of new such components and the occurrence of very high energy flares. Estimates on the physical parameters for both sources are given (Doppler factor, viewing angle, magnetic field, etc.).

Early results of AGN studies with the space VLB interferometer RadioAstron

AbstractThe space element of the ground-space very long baseline (VLB) interferometer RadioAstron is a 10-meter radio telescope Spektr-R which was successfully launched in 2011. It covers four frequency bands from 0.3 to 25 GHz and provides baselines up to 350,000 km. This allows to study space objects with a resolution as high as about 10 microarcseconds. Fringes are found at all four bands of 92, 18, 6, and 1.3 cm. Science observations are ongoing. Early results of the RadioAstron AGN survey at extreme angular resolutions will be presented in the talk. In particular, AGN core emission is successfully detected at interferometer baselines up to 7.6 GLambda (or fringe spacing 27 microarcseconds) which is the current VLBI record. High radio brightness of AGN cores is found significantly above the known inverse-Compton limit. Implications to AGN jet emission models will be discussed. First results of RadioAstron space VLBI imaging of AGN jets will be also presented.

PeV neutrinos observed by IceCube from cores of active galactic nuclei

I show that the high energy neutrino flux predicted to arise from AGN cores can explain the PeV neutrinos detected by Ice Cube without conflicting with the constraints from the observed extragalactic cosmic ray and gamma-ray backgrounds.

The radio structure of 3C 316, a galaxy with double-peaked narrow optical emission lines

The galaxy 3C\,316 is the brightest in the radio band among the optically-selected candidates exhibiting double-peaked narrow optical emission lines. Observations with the Very Large Array (VLA), Multi-Element Remotely Linked Interferometer Network (e-MERLIN), and the European VLBI Network (EVN) at 5\,GHz have been used to study the radio structure of the source in order to determine the nature of the nuclear components and to determine the presence of radio cores. The e-MERLIN image of 3C 316 reveals a collimated coherent east-west emission structure with a total extent of about 3 kpc. The EVN image shows seven discrete compact knots on an S-shaped line. However, none of these knots could be unambiguously identified as an AGN core. The observations suggest that the majority of the radio structure belongs to a powerful radio AGN, whose physical size and radio spectrum classify it as a compact steep-spectrum source. Given the complex radio structure with radio blobs and knots, the possibility of a kpc-separation dual AGN cannot be excluded if the secondary is either a naked core or radio quiet.

E-MERLIN observations at 5 GHz of the GOODS-N region: pinpointing AGN cores in high-redshift galaxies

We present 5 GHz e-MERLIN observations of the GOODS-N region at sub-arcsec resolution (0.2--0.5 arcsec). These data form part of the early commissioning observations for the e-MERLIN interferometer and a pilot for the e-MERLIN legacy program eMERGE. A total of 17 sources were detected with S/N>3. These observations provide unique information on the radio source morphology at sub-arcsec scales. For twelve of these sources, deeper 1.4 GHz MERLIN+VLA observations at the same spatial resolution are available, allowing radio spectral indices to be derived for ten sources on sub-arcsec angular scales. Via analysis of the spectral indices and radio morphologies, these sources have been identified as AGN cores in moderate-to-high redshift (1<z<4) galaxies. These results have provided AGN (or AGN candidate) classification for six previously unclassified sources and confirmed the AGN nature of the rest of the sample. Ultimately the eMERGE project will image the GOODS-N region at 1.4 and 5 GHz with higher resolution (about 50 mas at 5 GHz) and down to sub-microJy sensitivities. The unique combination of sensitivity and spatial resolution will be exploited to study star formation and AGN activity in distant galaxies.

Heteropolyhedral silver compounds containing the polydentate ligandN,N,O-E-[6-(hydroxyimino)ethyl]-1,3,7-trimethyllumazine. Preparation, spectral and XRD structural study and AIM calculations

The oxime derived from 6-acetyl-1,3,7-trimethyllumazine (1) ((E-6-(hydroxyimino)ethyl)-1,3,7-trimethylpteridine-2,4(1H,3H)-dione, DLMAceMox) has been prepared and its molecular and crystal structure determined from spectral and XRD data. The oxime ligand was reacted with silver nitrate, perchlorate, thiocyanate, trifluoromethylsulfonate and tetrafluoroborate to give complexes with formulas [Ag(2)(DLMAceMox)(2)(NO(3))(2)](n) (2), [Ag(2)(DLMAceMox)(2)(ClO(4))(2)](n) (3), [Ag(2)(DLMAceMox)(2)(SCN)(2)] (4), [Ag(2)(DLMAceMox)(2)(CF(3)SO(3))(2)(CH(3)CH(2)OH)]·CH(3)CH(2)OH (5) and [Ag(DLMAceMox)(2)]BF(4) (6). Single-crystal XRD studies show that the asymmetrical residual unit of complexes 2, 3 and 5 contains two quite different but connected silver centers (Ag1-Ag2, 2.9-3.2 Å). In addition to this, the Ag1 ion displays coordination with the N5 and O4 atoms from both lumazine moieties and a ligand (nitrato, perchlorato or ethanol) bridging to another disilver unit. The Ag2 ion is coordinated to the N61 oxime nitrogens, a monodentate and a (O,O)-bridging nitrato/perchlorato or two monodentate O-trifluoromethylsulfonato anions. The coordination polyhedra can be best described as a strongly distorted octahedron (around Ag1) and a square-based pyramid (around Ag2). The Ag-N and Ag-O bond lengths range between 2.22-2.41 and 2.40-2.67 Å, respectively. Although the structure of 4 cannot be resolved by XRD, it is likely to be similar to those described for 2, 3 and 5, containing Ag-Ag units with S-thiocyanato terminal ligands. Finally, the structure of the tetrafluoroborate compound 6 is mononuclear with a strongly distorted tetrahedral AgN(4) core (Ag-N, 2.27-2.43 Å). Always, the different Ag-N distances found clearly point to the more basic character of the oxime N61 nitrogen atom when compared with the pyrazine N5 one. A topological analysis of the electron density within the framework provided by the quantum theory of atoms in molecules (QTAIM) using DFT(M06L) levels of theory has been performed. Every Ag-Ag and Ag-ligand interaction has been characterized in terms of Laplacian of the electron density, [nabla](2)ρ(r), and the total energy density, H(r).

The effect of angular opening on the dynamics of relativistic hydro jets

Context. Relativistic jets emerging from AGN cores transfer energy from the core to their surrounding ISM/IGM. Because jets are observed to have finite opening angles, one needs to quantify the role of conical versus cylindrical jet propagation in this energy transfer. Aims. We use FR-II AGN jets parameter with finite opening angles. We study the effect of the variation of the opening angle on the dynamics and energy transfer of the jet. We also point out how the characteristics of this external medium, such as its density profile, play a role in the dynamics. Methods. This study exploits our parallel AMR code MPI-AMRVAC with its special relativistic hydrodynamic model, incorporating an equation of state with varying effective polytropic index. We studied mildly under-dense jets up to opening angles of 10 degrees, at Lorentz factors of about 10, inspired by observations. Instantaneous quantification of the various ISM volumes and their energy content allows one to quantify the role of mixing versus shock-heated cocoon regions over the time intervals. Results. We show that a wider opening angle jet results in a faster deceleration of the jet and leads to a wider cocoon dominated by Kelvin-Helmholtz and Rayleigh-Taylor instabilities. The energy transfer mainly occurs in the shocked ISM region by both the frontal bow shock and cocoon-traversing shock waves, in a roughly 3 to 1 ratio to the energy transfer of the mixing zone, for a 5 degree opening angle jet. A rarefaction wave induces a dynamically formed layered structure of the jet beam. Conclusions. Finite opening angle jets can efficiently transfer significant fractions (25 % up to 70 %) of their injected energy over a growing region of shocked ISM matter. The role of the ISM stratification is prominent for determining the overall volume that is affected by relativistic jet injection.

Optical properties of high-frequency radio sources from the Australia Telescope 20 GHz (AT20G) Survey

Our current understanding of radio-loud AGN comes predominantly from studies at frequencies of 5 GHz and below. With the recent completion of the Australia Telescope 20 GHz (AT20G) survey, we can now gain insight into the high-frequency radio properties of AGN. This paper presents supplementary information on the AT20G sources in the form of optical counterparts and redshifts. Optical counterparts were identified using the SuperCOSMOS database and redshifts were found from either the 6dF Galaxy survey or the literature. We also report 144 new redshifts. For AT20G sources outside the Galactic plane, 78.5% have optical identifications and 30.9% have redshift information. The optical identification rate also increases with increasing flux density. Targets which had optical spectra available were examined to obtain a spectral classification. There appear to be two distinct AT20G populations; the high luminosity quasars that are generally associated with point-source optical counterparts and exhibit strong emission lines in the optical spectrum, and the lower luminosity radio galaxies that are generally associated with passive galaxies in both the optical images and spectroscopic properties. It is suggested that these different populations can be associated with different accretion modes (cold-mode or hot-mode). We find that the cold-mode sources have a steeper spectral index and produce more luminous radio lobes, but generally reside in smaller host galaxies than their hot-mode counterparts. This can be attributed to the fact that they are accreting material more efficiently. Lastly, we compare the AT20G survey with the S-cubed semi-empirical (S3-SEX) models and conclude that the S3-SEX models need refining to correctly model the compact cores of AGN. The AT20G survey provides the ideal sample to do this.

Mini-radio lobes in AGN core illumination and their hadronic gamma-ray afterlight

Abstract Recent radio observations reveal the existence of mini-radio lobes in active galaxies with scales of ∼10 pc. The lobes are expected to be filled with shock-accelerated electrons and protons. In this work, we examine the photon spectra from the mini-lobes, properly taking the hadronic processes into account. We find that the resultant broad-band spectra contain the two distinct hadronic bumps in γ-ray bands, i.e. the proton synchrotron bump at ∼1 MeV and the synchrotron bump at ∼1 GeV due to the secondary electrons/positrons produced via photo-pion cascade. In particular, when the duration of particle injection is shorter than the lobe age, radio-dark γ-ray lobes are predicted. The existence of the γ-ray lobes could be testable with the future TeV–γ Cherenkov Telescope Array.