Distant Active Galactic Nuclei Research Articles

Cosmic dipoles of active galactic nuclei at optical and radio wavelengths display much larger amplitudes than the cosmic microwave background dipole

Abstract Sky distributions of large samples of distant active galactic nuclei (AGNs) have shown dipoles significantly larger than the cosmic microwave background (CMB) dipole. However, a recent Bayesian analysis of the QUAIA sample, comprising 1.3 million quasars, has yielded a dipole that seems to be in tandem with the CMB dipole, in contravention of most previous studies of AGN dipoles. Since the question has large cosmological implications, we investigate the QUAIA quasar sample afresh, by directly computing the dipole from asymmetries observed in the source number counts. We instead find a dipole 3-4 times as large as the CMB dipole though in the same direction. Further, it has been claimed elsewhere that the difference between the CMB dipole and the radio dipole estimated from the NRAO VLA Sky Survey (NVSS), the first large catalogue that showed an AGN dipole about four times larger than the CMB dipole, can be fully accounted for by incorporating the shot-noise and clustering contributions to the total NVSS dipole. A careful reinvestigation of the NVSS dipole, however, shows that the random phenomena like shot noise or clustering cannot account for the actually observed NVSS asymmetries, which show a systematic dipole pattern over the sky.

X-ray properties and obscured fraction of AGN in the J1030 Chandra field

The 500ks Chandra ACIS-I observation of the field around the z = 6.31 quasar SDSS J1030+0524 is currently the fifth deepest extragalactic X-ray survey. The rich multi-band coverage of the field allowed an effective identification and redshift determination of the X-ray source counterparts; to date, a catalog of 243 extragalactic X-ray sources with either a spectroscopic or photometric redshift estimate in the range z ≈ 0 − 6 is available over an area of 355 arcmin2. Given its depth and the multi-band information, this catalog is an excellent resource to investigate X-ray spectral properties of distant active galactic nuclei (AGN) and derive the redshift evolution of their obscuration. We performed a thorough X-ray spectral analysis for each object in the sample, and measured its nuclear column density NH and intrinsic (de-absorbed) 2–10 keV rest-frame luminosity, L2 − 10. Whenever possible, we also used the presence of the Fe Kα emission line to improve the photometric redshift estimates. We measured the fractions of AGN hidden by column densities in excess of 1022 and 1023 cm−2 (f22 and f23, respectively) as a function of L2 − 10 and redshift, and corrected for selection effects to recover the intrinsic obscured fractions. At z ∼ 1.2, we found f22 ∼ 0.7 − 0.8 and f23 ∼ 0.5 − 0.6, respectively, in broad agreement with the results from other X-ray surveys. No significant variations in X-ray luminosity were found within the limited luminosity range probed by our sample (log L2 − 10 ∼ 42.8 − 44.3). When focusing on luminous AGN with log L2 − 10 ∼ 44 to maximize the sample completeness up to large cosmological distances, we did not observe any significant change in f22 or f23 over the redshift range z ∼ 0.8 − 3. Nonetheless, the obscured fractions we measure are significantly higher than is seen in the local Universe for objects of comparable intrinsic luminosity, pointing toward an increase in the average AGN obscuration toward early cosmic epochs, as also observed in other X-ray surveys. We finally compared our results with recent analytic models that ascribe the greater obscuration observed in AGN at high redshifts to the dense interstellar medium (ISM) of their hosts. When combined with literature measurements, our results favor a scenario in which the total column density of the ISM and the characteristic surface density of its individual clouds both increase toward early cosmic epochs as NH, ISM∝(1 + z)δ, with δ ∼ 3.3 − 4 and Σc, * ∝ (1 + z)2, respectively.

Lightning: An X-Ray to Submillimeter Galaxy SED-fitting Code with Physically Motivated Stellar, Dust, and AGN Models

We present an updated version of Lightning, a galaxy spectral energy distribution (SED) fitting code that can model X-ray to submillimeter observations. The models in Lightning include the options to contain contributions from stellar populations, dust attenuation and emission, and active galactic nuclei (AGNs). X-ray emission, when utilized, can be modeled as originating from stellar compact binary populations with the option to include emission from AGNs. We have also included a variety of algorithms to fit the models to observations and sample parameter posteriors; these include adaptive Markov Chain Monte Carlo (MCMC), affine-invariant MCMC, and Levenberg–Marquardt gradient-descent (MPFIT) algorithms. To demonstrate some of the capabilities of Lightning, we present several examples using a variety of observational data. These examples include (1) deriving the spatially resolved stellar properties of the nearby galaxy M81, (2) demonstrating how X-ray emission can provide constraints on the properties of the supermassive black hole of a distant AGN, (3) exploring how to rectify the attenuation effects of inclination on the derived the star formation rate of the edge-on galaxy NGC 4631, (4) comparing the performance of Lightning to similar Bayesian SED-fitting codes when deriving physical properties of the star-forming galaxy NGC 628, and (5) comparing the derived X-ray and UV-to-IR AGN properties from Lightning and CIGALE for a distant AGN. Lightning is an open-source application developed in IDL and is available at https://github.com/rafaeleufrasio/lightning.

A Multioctave 8 GHz$-$40 GHz Receiver for Radio Astronomy

Accurate measurement of angular positions on the sky requires a well-defined system of reference, something that in practice is realized by the International Celestial Reference Frame (ICRF) with observations of distant (typical redshift <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 1) Active Galactic Nuclei (AGN). At such great distances a subset of these objects exhibit as little as 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 50 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> as/year observed parallax or proper motion, thus giving the frame excellent spatial and temporal stability. Until fairly recently the majority of AGN centered imaging was accomplished in the S (2.3 GHz) and X (8.4 GHz) radio frequency bands, however S-band observations for reasons such as sensitivity “plateauing”, increased source structure (jets), and radio frequency interference (RFI) have become less productive. Following spacecraft telemetry moves to higher frequencies and a desire to strengthen JPL's leadership in defining the next-generation of celestial reference frames has motivated the development of a “Quad-band” prototype receiver that operates in X, Ku, K, and Ka band in both right hand (RCP) and left hand (LCP) circular polarization. The goal of this receiver is to achieve less than a 20 % increase in noise over the Jansky Very Large Array (JVLA, NRAO) performance specification, which in such a wide bandwidth represents a revolutionary capability. To evaluate the various technical developments of the 8 GHz <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 40 GHz receiver the feedhorn optical beam was designed to interface to the US based Very Long Baseline Array (VLBA). The receiver's intermediate frequency (IF) spans 4 GHz <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 8 GHz, giving rise to up to eight 4 GHz IF channels for a fully populated instrument. This paper outlines the technical development of a 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{1}$</tex-math></inline-formula> / <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> octave wide (8 GHz <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 40 GHz) X-Ka band prototype receiver, fulfilling a need for super broadband technology within the VLBI network. An important additional benefit of the wideband receiver approach is its simplicity and low cost of operation.

What’s behind the corner: Maser emission in nearby and distant galaxies with the new radio facilities

AbstractExtragalactic maser sources are unique tools to derive fundamental physical quantities of the host galaxies, e.g, geometry of accretion disks around super-massive black holes and precise black hole masses, and study in detail the interaction region of nuclear jets/outflows with the interstellar medium, in nearby and distant Active Galactic Nuclei. So far, however, extragalactic maser searches have yielded detection of few percent, and only relatively few maser sources have been found. Because of their unprecedented sensitivity, new upcoming facilities, like the SKA and the ngVLA, will allow to significantly increase the number of known (water) maser sources. This will lead to the chance of performing statistically-relevant studies of the maser phenomenon (and its occurrence), derive extragalactic masers luminosity functions, and ultimately (in particular, through the aid of longer-baselines arrays options) to perform the studies described above for larger samples and up to cosmological distances.

Subarcsecond view on the high-redshift blazar GB 1508+5714 by the International LOFAR Telescope

Context. Studies of the most distant active galactic nuclei (AGNs) allow us to test our current understanding of the physics present in radio-jetted AGNs across a range of environments, and probe their interactions with these environments. The decrease in apparent luminosity with distance is the primary difficulty to overcome in the study of these distant AGNs, which requires highly sensitive instruments. Aims. Our goal is to employ new long wavelength radio data to better parametrise the broad-band spectral energy distribution (SED) of GB 1508+5714, a high-redshift (z = 4.30) AGN. Its high redshift, high intrinsic luminosity and classification as a blazar allow us to test emission models that consider the efficient cooling of jet electrons via inverse Compton losses in interactions with the dense cosmic microwave background (CMB) photon field at high redshifts. A significant detection of this effect in GB 1508+5714 may partly explain the apparent sparsity of high-redshift radio galaxies in wide-field surveys, detections of this kind are only becoming possible with the current generation of Square Kilometre Array (SKA) precursors. Methods. We used the LOw-Frequency ARray (LOFAR) to image the long wavelength radio emission around the high-redshift blazar GB 1508+5714 on arcsecond scales at frequencies between 128 and 160 MHz. This allowed us to compare the spatially resolved structure with higher frequency observations, and construct spectral index maps to study the spectral properties of the different components. Results. The LOFAR image shows a compact unresolved core and two resolved emission regions around 2 arcsec to the east and to the west of the radio core. We find structure consistent with previous Very Large Array (VLA) observations, as well as a previously unreported emission region to the east. The region in the west shows a spectral index of −1.2−0.2+0.4 while the region in the east indicates a spectral index of ≲−1.1. The radio core features aflat spectral index of 0.02 ± 0.01. Conclusions. We interpret the arcsecond-scale radio structure of GB 1508+5714 as a FR II-like radio galaxy at a small viewing angle, and the western component as the region containing the approaching jet’s terminal hot spot while the eastern diffuse component near the core can be interpreted as the counter-hot spot region. Our SED modelling shows that a scenario featuring significant quenching effects caused by interaction with the CMB provides a good description of the data, and notably explains the suppressed radio emission.

Solar system peculiar motion from the Hubble diagram of quasars and testing the cosmological principle

ABSTRACTWe determine here the peculiar motion of the Solar system, first time from the m–z Hubble diagram of quasars. Observer’s peculiar motion causes a systematic shift in the m–z plane between sources lying along the velocity vector and those in the opposite direction, providing a measure of the peculiar velocity. Accordingly, from a sample of ∼1.2 × 105 mid-infrared quasars with measured spectroscopic redshifts, we arrive at a peculiar velocity ∼22 times larger than that from the cosmic microwave background radiation (CMBR) dipole but direction matching within ∼2σ. Previous findings from number count, sky brightness, or redshift dipoles observed in samples of distant active galactic nuclei or supernovae type Ia too had yielded values 2–10 times larger than the CMBR value, though the direction in all cases agreed with the CMBR dipole. Since a genuine solar peculiar velocity cannot vary from one data set to another, an order of magnitude, statistically significant, discordant dipoles might imply that we may instead have to look for some other cause for the genesis of these dipoles, including that of the CMBR. At the same time, a common direction for all these dipoles, determined from completely independent surveys by different groups employing different techniques, might indicate that these dipoles are not resulting from some systematics in the observations or in the data analysis, but could instead suggest a preferred direction in the Universe due to an inherent anisotropy, which, in turn, would be against the cosmological principle, the most basic tenet of the modern cosmology.

Our Peculiar Motion Inferred from Number Counts of Mid Infra Red AGNs and the Discordance Seen with the Cosmological Principle

According to the Cosmological Principle, the Universe is isotropic and no preferred direction would be seen by an observer that might be stationary with respect to the expanding cosmic fluid. However, because of observer’s partaking in the solar system peculiar motion, there would appear in some of the observed properties of the Cosmos a dipole anisotropy, which could in turn be exploited to determine the peculiar motion of the solar system. The dipole anisotropy in the Cosmic Microwave Background Radiation (CMBR) has given a peculiar velocity vector 370 km s−1 along l=264∘,b=48∘. However, some other dipoles, for instance, from the number counts, sky brightness or redshift distributions in large samples of distant Active Galactic Nuclei (AGNs), have yielded values of the peculiar velocity many times larger than that from the CMBR, though surprisingly, in all cases the directions agreed with the CMBR dipole. Here we determine our peculiar motion from a sample of 0.28 million AGNs, selected from the Mid Infra Red Active Galactic Nuclei (MIRAGN) sample comprising more than a million sources. From this, we find a peculiar velocity, which is more than four times the CMBR value, although the direction seems to be within ∼2σ of the CMBR dipole. A genuine value of the solar peculiar velocity should be the same irrespective of the data or the technique employed to estimate it. Therefore, such discordant dipole amplitudes might mean that the explanation for these dipoles, including that of the CMBR, might in fact be something else. The observed fact that the direction in all cases is the same, though obtained from completely independent surveys using different instruments and techniques, by different sets of people employing different computing routines, might nonetheless indicate that these dipoles are not merely due to some systematics, otherwise why would they all be pointing along the same direction. It might instead suggest a preferred direction in the Universe, implying a genuine anisotropy, which would violate the Cosmological Principle, the core of the modern cosmology.

The ROSAT Raster survey in the north ecliptic pole field

The north ecliptic pole (NEP) is an important region for extragalactic surveys. Deep and wide contiguous surveys are being performed by several space observatories, most currently with the eROSITA telescope. Several more are planned for the near future. We analyse all the ROSAT pointed and survey observations in a region of 40 deg2 around the NEP, restricting the ROSAT field of view to the inner 30′ radius. We obtain an X-ray catalogue of 805 sources with 0.5−2 keV fluxes &gt; 2.9 × 10−15 erg cm−2 s−1, about a factor of three deeper than the ROSAT All-Sky Survey in this field. The sensitivity and angular resolution of our data are comparable to the eROSITA All-Sky Survey expectations. The 50% position error radius of the sample of X-ray sources is ∼10″. We use HEROES optical and near-infrared imaging photometry from the Subaru and Canada/France/Hawaii telescopes together with GALEX, SDSS, Pan-STARRS, and WISE catalogues, as well as images from a new deep and wide Spitzer survey in the field to statistically identify the X-ray sources and to calculate photometric redshifts for the candidate counterparts. In particular, we utilize mid-infrared (mid-IR) colours to identify active galactic nucleus (AGN) X-ray counterparts. Despite the relatively large error circles and often faint counterparts, together with confusion issues and systematic errors, we obtain a rather reliable catalogue of 766 high-quality optical counterparts, corresponding redshifts and optical classifications. The quality of the dataset is sufficient to look at ensemble properties of X-ray source classes. In particular we find a new population of luminous absorbed X-ray AGN at large redshifts, identified through their mid-IR colours. This populous group of AGN was not recognized in previous X-ray surveys, but could be identified in our work due to the unique combination of survey solid angle, X-ray sensitivity, and quality of the multi-wavelength photometry. We also use the WISE and Spitzer photometry to identify a sample of 185 AGN selected purely through their mid-IR colours, most of which are not detected by ROSAT. Their redshifts and upper limits to X-ray luminosity and X-ray–to–optical flux ratios are even higher than for the new class of X-ray selected luminous type 2 AGN (AGN2); they are probably a natural extension of this sample. This unique dataset is important as a reference sample for future deep surveys in the NEP region, in particular for eROSITA and also for Euclid and SPHEREX. We predict that most of the absorbed distant AGN should be readily picked up by eROSITA, but they require sensitive mid-IR imaging to be recognized as optical counterparts.

Liverpool-Maidanak monitoring of the Einstein Cross in 2006–2019

Quasar microlensing offers a unique opportunity to resolve tiny sources in distant active galactic nuclei and study compact object populations in lensing galaxies. We therefore searched for microlensing-induced variability of the gravitationally lensed quasar QSO 2237+0305 (Einstein Cross) using 4374 optical frames taken with the 2.0 m Liverpool Telescope and the 1.5 m Maidanak Telescope. These gVrRI frames over the 2006–2019 period were homogeneously processed to generate accurate long-term multi-band light curves of the four quasar images A–D. Through difference light curves, we found strong microlensing signatures. We then focused on the analytical modelling of two putative caustic-crossing events in image C, finding compelling evidence that this image experienced a double caustic crossing. Additionally, our overall results indicate that a standard accretion disc accounts reasonably well for the brightness profile of UV continuum emission sources and for the growth in source radius when the emission wavelength increases: Rλ ∝ λα, α = 1.33 ± 0.09. However, we caution that numerical microlensing simulations are required before firm conclusions can be reached on the UV emission scenario because the VRI-band monitoring during the first caustic crossing and one of our two α indicators lead to a few good solutions with α ≈ 1.

A transition from parabolic to conical shape as a common effect in nearby AGN jets

ABSTRACT Observational studies of collimation in jets in active galactic nuclei (AGN) are a key to understanding their formation and acceleration processes. We have performed an automated search for jet shape transitions in a sample of 367 AGN using VLBA data at 15 and 1.4 GHz. This search has found 10 out of 29 nearby jets at redshifts z &amp;lt; 0.07 with a transition from a parabolic to conical shape, while the full analysed sample is dominated by distant AGN with a typical z ≈ 1. The ten AGN are UGC 00773, NGC 1052, 3C 111, 3C 120, TXS 0815−094, Mrk 180, PKS 1514+00, NGC 6251, 3C 371, and BL Lac. We conclude that the geometry transition may be a common effect in AGN jets. It can be observed only when sufficient linear resolution is obtained. Supplementing these results with previously reported shape breaks in the nearby AGN 1H 0323+342 and M87, we estimate that the break occurs at 105–106 gravitational radii from the nucleus. We suggest that the jet shape transition happens when the bulk plasma kinetic energy flux becomes equal to the Poynting energy flux, while the ambient medium pressure is assumed to be governed by Bondi accretion. In general, the break point may not coincide with the Bondi radius. The observational data support our model predictions on the jet acceleration and properties of the break point.

Search for spectral features in extragalactic background light with gamma-ray telescopes

Context. Cumulative optical and infrared emission from galaxies accumulated over cosmological time scales, the extragalactic background light (EBL), could be probed by complementary techniques of direct observations and source counting in the visible and infrared as well as via its imprint on the signal of distant active galactic nuclei in γ-rays. Aims. We compare the visible and infrared measurements with the γ-ray constraints and study if the discrepancies of the measurements with different methods could be due to the presence of features in the EBL spectrum that are localised in the micron wavelength range. Methods. We combined data on time-averaged spectra of selected blazars that were obtained by Fermi and ground-based gamma-ray telescopes. We also modelled the effect of absorption on EBL while allowing for the existence of a previously unaccounted spectral feature. Results. We show that a previously reported “excess” in EBL flux in the ∼1 micron wavelength range is consistent with γ-ray measurements, that is, if the excess has the form of a narrow feature of the width δλ &lt; λ and an overall flux of up to 15 nW m−2 sr−1 above the “minimal” EBL, which is estimated from the visible and infrared source counts. Such ’bump-like’ spectral features could originate, for example, from decaying dark-matter particles, or either axions or peculiar astrophysical processes in the course of star-formation history. We discuss the possibilities for the search of spectral features in the EBL with the Cherenkov Telescope Array.

Reverberation Measurements of the Inner Radii of the Dust Tori in Quasars

Abstract We present the results of a dust-reverberation survey of quasars at redshifts z &lt; 0.6. We found a delayed response of the K-band flux variation after the optical flux variation in 25 out of 31 targets, and obtained the lag time between them for 22 targets. Combined with the results for nearby Seyfert galaxies, we provide the largest homogeneous collection of K-band dust-reverberation data for 36 type 1 active galactic nuclei (AGNs). This doubles the sample and includes the most distant AGN and the largest lag so far measured. We estimated the optical luminosity of the AGN component of each target using three different methods: spectral decomposition, the flux-variation-gradient method, and image decomposition. We found a strong correlation between the reverberation radius for the innermost dust torus and the optical luminosity over a range of approximately four orders of magnitude in luminosity, as is already known for Seyfert galaxies. We estimated the luminosity distances of the AGNs based on their dust-reverberation lags, and found that the data in the redshift–distance diagram are consistent with the current standard estimates of the cosmological parameters. We also present the radius–luminosity relations for isotropic luminosity indicators such as the hard X-ray (14–195 keV), [O IV] 25.89 μm, and mid-infrared (12 μm) continuum luminosities, which are applicable to obscured AGNs.

LOFAR measures the hotspot advance speed of the high-redshift blazar S5 0836+710

Context. The emission and proper motion of the terminal hotspots of active galactic nucleus (AGN) jets can be used as a powerful probe of the intergalactic medium. However, measurements of hotspot advance speeds in active galaxies are difficult, especially in the young universe, because of the low angular velocities and the low brightness of distant radio galaxies. Aims. Our goal is to study the termination of an AGN jet in the young universe and to deduce physical parameters of the jet and the intergalactic medium. Methods. We used the LOw Frequency ARray (LOFAR) to image the long-wavelength radio emission of the high-redshift blazar S5 0836+710 on arcsecond scales between 120 MHz and 160 MHz. Results. The LOFAR image shows a compact unresolved core and a resolved emission region about 1.5 arcsec to the southwest of the radio core. This structure is in general agreement with previous higher-frequency radio observations with the Multi-Element Radio-Linked Interferometer Network (MERLIN) and the Very Large Array (VLA). The southern component shows a moderately steep spectrum with a spectral index of about ≳ − 1, and the spectral index of the core is flat to slightly inverted. In addition, we detect for the first time a resolved steep-spectrum halo with a spectral index of about −1 surrounding the core. Conclusions. The arcsecond-scale radio structure of S5 0836+710 can be understood as a Faranoff–Riley (FR) II radio galaxy observed at a small viewing angle. The southern component can be interpreted as the region of the approaching jet’s terminal hotspot, and the halo like diffuse component near the core can be interpreted as the counter-hotspot region. From the differential Doppler boosting of both features, we can derive the hotspot advance speed to (0.01 − 0.036) c. At a constant advance speed, the derived age of the source would exceed the total lifetime of such a powerful FR II radio galaxy substantially. Thus, the hotspot advance speed must have been higher in the past, in agreement with a scenario in which the originally highly relativistic jet has lost collimation as a result of instability growth and has transformed into an only mildly relativistic flow. Our data suggest that the density of the intergalactic medium around this distant (z = 2.22) AGN could be substantially higher than the values typically found in less distant FR II radio galaxies.

Photometric Reverberation Mapping of AGNs at 0.1 &lt; z &lt;0.8. I. Observational Technique

The improvement of the calibration relation for determining the size of the broad-line region from the observed optical luminosity of active galactic nuclei (AGN) is a necessary task to study fundamental parameters of distant AGNs such as mass of the central supermassive black hole. The most popular method of the BLR size estimation is the reverberation mapping based on measuring the time delay between the continuum flux and the flux in the emission lines. In our work, we apply the method of photometric reverberation mapping in medium-band filters, adapted for observations at the Zeiss-1000 telescope of the SAO RAS, for the study of AGN with broad lines in the range of redshifts $0.1 < z < 0.8$. This paper describes the technique of observations and data processing, provides a sample of objects and demonstrates the stability of the used method. As a preliminary result for 2MASX J08535955+7700543 at $z=0.1$ we have obtained time delay estimates of $\tau (ICCF)=32.2^{\pm10.6}$ days and $\tau(JAVELIN)=39.5_{-15.8}^{+23.0}$ days that are consistent with each other and also within the accuracy of the existing calibration relations.

Relationship Between the Spins and Masses of Supermassive Black Holes in Distant Active Galactic Nuclei with z &gt; 4

Hybrid models for the generation of relativistic jets are used to place constraints on the spins of supermassive black holes (SMBHs) in active galactic nuclei at redshifts z > 4.0. It is shown that these SMBHs possess spins that are far from the limiting Kerr value. Mass-spin diagrams show that, on average, the spin grows with the mass of the black hole. The results obtained can be compared to the results of numerical simulations of the evolution of the masses and spins of SMBHs, opening the possibility of studies of the character of the accretion in the galaxies hosting these objects.

The jet of S5 0716[formula omitted]71 at [formula omitted]as scales with RadioAstron

Ground-space interferometer RadioAstron provides unique opportunity to probe detail structure of the distant active galactic nuclei at μas scales. Here we report on RadioAstron observations of the BL Lac object S5 0716+71, performed in a framework of the AGN Polarization and Survey Key Science Programs at 22 GHz during 2012–2018. We obtained the highest angular resolution image of the source to date, at 57×24μas. It reveals complex structure of the blazar jet in the inner 100 μas, with emission regions that can be responsible for the blazar variability at timescales of a few days to week. Linear polarization is detected in the core and jet areas at the projected baselines up to about 5.6 Earth diameters. The observed core brightness temperature in the source frame of ⩾2.2×1013 K is in excess of theoretical limits, suggesting the physical conditions are far from the equipartition between relativistic particles and magnetic field.

Variability-selected Low-luminosity Active Galactic Nuclei Candidates in the 7 Ms Chandra Deep Field-South

Abstract In deep X-ray surveys, active galactic nuclei (AGNs) with a broad range of luminosities have been identified. However, cosmologically distant low-luminosity AGN (LLAGN, erg s−1) identification still poses a challenge because of significant contamination from host galaxies. Based on the 7 Ms Chandra Deep Field-South (CDF-S) survey, the longest-timescale (∼17 years) deep X-ray survey to date, we utilize an X-ray variability selection technique to search for LLAGNs that remain unidentified among the CDF-S X-ray sources. We find 13 variable sources from 110 unclassified CDF-S X-ray sources. Except for one source that could be an ultraluminous X-ray source, the variability of the remaining 12 sources is most likely due to accreting supermassive black holes. These 12 AGN candidates have low intrinsic X-ray luminosities, with a median value of 7 × 1040 erg s−1. They are generally not heavily obscured, with an average effective power-law photon index of 1.8. The fraction of variable AGNs in the CDF-S is independent of X-ray luminosity and is only restricted by the total number of observed net counts, confirming previous findings that X-ray variability is a near-ubiquitous property of AGNs over a wide range of luminosities. There is an anticorrelation between X-ray luminosity and variability amplitude for high-luminosity AGNs, but as the luminosity drops to ≲1042 erg s−1, the variability amplitude no longer appears dependent on the luminosity. The entire observed luminosity–variability trend can be roughly reproduced by an empirical AGN variability model based on a broken power-law power spectral density function.

Deep ALMA photometry of distant X-ray AGN: improvements in star formation rate constraints, and AGN identification

We present the star formation rates (SFRs) of a sample of 109 galaxies with X-ray selected active galactic nuclei (AGN) with moderate to high X-ray luminosities (L(2-8keV)= 10^42-10^45 erg/s), at redshifts 1 < z < 4.7, that were selected to be faint or undetected in the Herschel bands. We combine our deep ALMA continuum observations with deblended 8-500{\mu}m photometry from Spitzer and Herschel, and use infrared (IR) SED fitting and AGN - star formation decomposition methods. The addition of the ALMA photometry results in an order of magnitude more X-ray AGN in our sample with a measured SFR (now 37%). The remaining 63% of the sources have SFR upper limits that are typically a factor of 2-10 times lower than the pre-ALMA constraints. With the improved constraints on the IR SEDs, we can now identify a mid-IR (MIR) AGN component in 50% of our sample, compared to only ~1% previously. We further explore the F870{\mu}m/F24{\mu}m-redshift plane as a tool for the identification of MIR emitting AGN, for three different samples representing AGN dominated, star formation dominated, and composite sources. We demonstrate that the F870{\mu}m/F24{\mu}m-redshift plane can successfully split between AGN and star formation dominated sources, and can be used as an AGN identification method.

Contribution of parsec-scale material on to the polarized X-ray spectrum of type 1 Seyfert galaxies

Type-1 radio-quiet active galactic nuclei (AGN) are seen from the polar direction and offer a direct view of their central X-ray engine. If most of X-ray photons have traveled from the primary source to the observer with minimum light-matter interaction, a fraction of radiation is emitted at different directions and is reprocessed by the parsec-scale equatorial circumnuclear region or the polar outflows. It is still unclear how much the polarization expected from type-1 AGN is affected by radiation that have scattered on the distant AGN components. In this paper, we examine the contribution of remote material onto the polarized X-ray spectrum of type-1 Seyfert galaxies using radiative transfer Monte Carlo codes. We find that the observed X-ray polarization strongly depends on the initial polarization emerging from the disk-corona system. For unpolarized and parallelly polarized photons (parallel to the disk), the contribution is negligible below 3 keV and tends to increase the polarization degree by up to one percentage points at higher energies, smoothing out the energy-dependent variations of the polarization angle. For perpendicularly polarized corona photons, the addition of the circumnuclear scattered (parallel) component adds to the polarization above 10 keV, decreases polarization below 10 keV and shifts the expected 90 deg rotation of the polarization angle to lower energies. In conclusion, we found that simulations of Seyfert-1s that do not account for reprocessing on the parsec-scale equatorial and polar material are under- or over-estimating the X-ray polarization by 0.1 - 1 percentage points.