Regions Of Active Galactic Nuclei Research Articles

Modeling the Reverberation Response of the Broad-line Region in Active Galactic Nuclei

The variable continuum emission of an active galactic nucleus (AGN) produces corresponding responses in the broad emission lines, which are modulated by light travel delays, and contain information on the physical properties, structure, and kinematics of the emitting gas region. The reverberation mapping technique, a time series analysis of the driving light curve and response, can recover some of this information, including the size and velocity field of the broad-line region (BLR). Here we introduce a new forward-modeling tool, the Broad Emission Line MApping Code, which simulates the velocity-resolved reverberation response of the BLR to any given input light curve by setting up a 3D ensemble of gas clouds for various specified geometries, velocity fields, and cloud properties. In this work, we present numerical approximations to the transfer function by simulating the velocity-resolved responses to a single continuum pulse for sets of models representing a spherical BLR with a radiatively driven outflow and a disklike BLR with Keplerian rotation. We explore how the structure, velocity field, and other BLR properties affect the transfer function. We calculate the response-weighted time delay (reverberation “lag”), which is considered to be a proxy for the luminosity-weighted radius of the BLR. We investigate the effects of anisotropic cloud emission and matter-bounded (completely ionized) clouds and find the response-weighted delay is only equivalent to the luminosity-weighted radius when clouds emit isotropically and are radiation-bounded (partially ionized). Otherwise, the luminosity-weighted radius can be overestimated by up to a factor of 2.

To test RNLRs−LO3 relation for narrow emission line regions of AGNs through low-redshift Type-2 AGNs in SDSS

ABSTRACT Sizes of narrow emission line regions (NLRs) of active galactic nuclei (AGNs) could be estimated by [O iii] line luminosity LO3 through the known RNLRs−LO3 empirical relations. Unfortunately, it is not convenient to test the RNLRs− LO3 empirical relations through structure properties of spatially resolved NLRs of large samples of AGNs. In this manuscript, a method is proposed to test the $R_{\mathrm{ NLRs}}\!\!-\!\!L_{\mathrm{ O3}}^{\sim 0.25}$ empirical relations for AGN NLRs through Sloan Digital Sky Survey (SDSS) Type-2 AGNs having few orientation effects on NLR sizes expected by the AGN unified model, after considering sizes Rfib of SDSS fibre-covered regions. Comparing Rfib and RNLRs estimated by LO3, Type-2 AGNs with Rfib > RNLRs (Sample-II) and with Rfib < RNLRs (Sample-I) should have different physical properties of NLRs. Accepting electron density gradients in AGN NLRs, statistically higher electron densities (traced by lower flux ratio RS2 of [S ii] λ6717 Å to [S ii] λ6731 Å) could be expected for the Type-2 AGNs in the Sample-I. Then, through the collected 1062 SDSS Type-2 AGNs in the Sample-I and 3658 SDSS Type-2 AGNs in the Sample-II, statistically lower RS2 for the Type-2 AGNs in the Sample-I can be confirmed with confidence level higher than 5σ, even after considering necessary effects. Therefore, the results in this manuscript can provide strong clues to support that the reported $R_{\mathrm{ NLRs}}~\propto ~L_{\mathrm{ O3}}^{0.25}$ empirical relation is preferred to estimate NLR sizes of SDSS AGNs through SDSS fibre spectroscopic results, and also to support the commonly expected electron density gradients in AGN NLRs.

Classifying Intermediate-redshift Galaxies in SDSS: Alternative Diagnostic Diagrams

We select a sample of 1437 active galactic nuclei (AGN) from the catalog of the Sloan Digital Sky Survey galaxy properties from the Portsmouth group by detection of the high-ionization [Ne v] 3426 Å emission line. We compare the fluxes of [Ne III] 3869 Å, [O III] 5007 Å, [O II] 3726, 3728 Å, and [O i] 6300 Å to that of [Ne v]. All four lines show a strong linear correlation with [Ne v], although lines from ions with lower ionization potentials have a lower correlation coefficient. We investigate the use of two forbidden line ratio diagnostic diagrams that do not rely on Hα in order to classify high-redshift galaxies. These use the [Ne III]/[O II] line ratio plotted against [O III]/[O i] and [O III]/[O II], respectively. We use photoionization modeling to characterize the behavior of the narrow-line region in AGN and star-forming regions and test the validity of our diagnostic diagrams. We also use a luminosity cutoff of log L [O III] [erg s−1] = 42, which lowers the contamination of the AGN region by star-forming galaxies down to 10% but does not remove green pea and purple grape galaxies from the AGN region. We also investigate the OHNO diagram, which uses [Ne III]/[O II] plotted against [O III]/Hβ. Using our new diagnostic diagrams, we are able to reliably classify AGN up to a redshift of z ≤ 1.06 and add more than 822 new AGN to the [Ne v]-selected AGN sample.

A small and vigorous black hole in the early Universe

Several theories have been proposed to describe the formation of black hole seeds in the early Universe and to explain the emergence of very massive black holes observed in the first thousand million years after the Big Bang1–3. Models consider different seeding and accretion scenarios4–7, which require the detection and characterization of black holes in the first few hundred million years after the Big Bang to be validated. Here we present an extensive analysis of the JWST-NIRSpec spectrum of GN-z11, an exceptionally luminous galaxy at z = 10.6, revealing the detection of the [Neiv]λ2423 and CII*λ1335 transitions (typical of active galactic nuclei), as well as semi-forbidden nebular lines tracing gas densities higher than 109 cm−3, typical of the broad line region of active galactic nuclei. These spectral features indicate that GN-z11 hosts an accreting black hole. The spectrum also reveals a deep and blueshifted CIVλ1549 absorption trough, tracing an outflow with velocity 800−1,000 km s−1, probably driven by the active galactic nucleus. Assuming local virial relations, we derive a black hole mass of log(MBH/M⊙)=6.2±0.3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\log ({M}_{{\\rm{BH}}}/{M}_{\\odot })=6.2\\pm 0.3$$\\end{document}, accreting at about five times the Eddington rate. These properties are consistent with both heavy seeds scenarios and scenarios considering intermediate and light seeds experiencing episodic super-Eddington phases. Our finding explains the high luminosity of GN-z11 and can also provide an explanation for its exceptionally high nitrogen abundance.

TANAMI: Tracking active galactic nuclei with austral milliarcsecond interferometry

Context. With the emergence of very high energy astronomy (VHE; E > 100 GeV), new open questions were presented to astronomers studying the multi-wavelength emission from blazars. Answers to these open questions, such as the Doppler crisis, and finding the location of the high-energy activity have eluded us thus far. Recently, quasi-simultaneous multi-wavelength monitoring programs have shown considerable success in investigating blazar activity. Aims. Such quasi-simultaneous observations across the electromagnetic spectrum became possible thanks to the launch of the Fermi Gamma-ray Space Telescope in 2008. In addition, with very long baseline interferometry (VLBI) observations, we can resolve the central parsec region of active galactic nuclei (AGN) and compare morphological changes to γ-ray activity in order to study high-energy-emitting blazars. To achieve our goals, we need sensitive, long-term VLBI monitoring of a complete sample of VHE-detected AGN. Methods. We performed VLBI observations of TeV-detected AGN and high-likelihood neutrino associations as of December of 2021 with the Long Baseline Array (LBA) and other southern-hemisphere radio telescopes at 2.3 GHz. Results. In this paper, we present first light TANAMI S-band images, focusing on the TeV-detected subsample of the full TANAMI sample. In addition to these VHE-detected sources, we show images of two flux density calibrators and two additional sources included in the observations. We study the redshift, 0.1–100 GeV photon flux, and S-band core brightness temperature distributions of the TeV-detected objects, and find that flat-spectrum radio quasars and low-synchrotron-peaked sources on average show higher brightness temperatures than high-synchrotron-peaked BL Lacs. Sources with bright GeV γ-ray emission also show higher brightness temperature values than γ-low sources. Conclusions. Long-term monitoring programs are crucial for studying the multiwavelength properties of AGN. With the successful detection of even the faintest sources, with flux densities below 50 mJy, future work will entail kinematic analysis and spectral studies both at 2.3 and 8.4 GHz to investigate the connection between the radio and γ-ray activity of these objects.

FRAMEx. V. Radio Spectral Shape at Central Subparsec Region of Active Galactic Nuclei

We present results from the Very Long Baseline Array multifrequency (1.6, 4.4, 8.6, and 22 GHz), high-sensitivity (∼25 μJy beam−1), subparsec-scale (<1 pc) observations and spectral energy distributions for a sample of 12 local active galactic nuclei (AGNs), a subset from our previous volume-complete sample with hard-X-ray (14–195 keV) luminosities above 1042 erg s−1, out to a distance of 40 Mpc. All 12 of the sources presented here were detected in the C (4.4 GHz) and X (8.6 GHz) bands, 75% in the L band (1.6 GHz), and 50% in the K band (22 GHz). Most sources showed compact, resolved/slightly resolved, central subparsec-scale radio morphology, except for a few with extended outflow-like features. A couple of sources have an additional component that may indicate the presence of a dual-core, single or double-sided jet or a more intricate feature, such as radio emission resulting from interaction with the nearby interstellar medium. The spectral slopes are mostly gigahertz-peaked or curved, with a few showing steep, flat, or inverted spectra. We found that at the subparsec scale, the gigahertz-peaked spectra belong to the low-accreting, radio-loud AGNs, with a tendency to produce strong outflows, possibly small-scale jets, and/or have a coronal origin. In contrast, flat/inverted spectra suggest compact radio emission from the central regions of highly accreting AGNs, possibly associated with radio-quiet AGNs producing winds/shocks or nuclear star formation in the vicinity of black holes.

Broad-line region in active galactic nuclei: Dusty or dustless?

Context. Dust in active galactic nuclei is clearly present right outside the broad-line region (BLR) in the form of a dusty molecular torus. However, some models of the BLR predict that dust may also exist within the BLR. Aims. We study the reprocessing of radiation by the BLR with the aim of observing how the presence of dust affects the reprocessed continuum and the line properties. Methods. We calculated a range of models using the CLOUDY photoionisation code for dusty and dustless plasma. We paid particular attention to the well-studied object NGC 5548, and we compared the line equivalent width predictions with the data from observations for this object. Results. We obtained a rough agreement between the expected equivalent widths of the Hβ and Mg II lines and the observed values for NGC 5548 for the line distances implied by the time-delay measurement (for Hβ) and the radius-luminosity relation (for Mg II) when the medium is dusty. We found the incident radiation to be consistent with the radiation seen by the observer, so no shielding between the inner disc and the BLR is required. High ionisation lines such as He II, however, clearly form in the inner dustless region. When the additional absorber is present, the Hβ emitting region moves closer to the dustless part of the accretion disc surface.

A New Photoionization Model of the Narrow-line Region in Active Galactic Nuclei

The photoionization model of narrow-line regions in active galactic nuclei (AGNs) has been investigated for decades. Many published models are restricted to simple linear scaling abundance relations, dust-free assumption, uniform AGN radiation field, and using one specific photoionization code, which restricts them from providing a satisfactory prediction on a broad range of AGN observations. Through a comprehensive investigation, here we present how the choice of abundance scaling relations, dust inclusion, AGN radiation fields, and different photoionization codes CLOUDY and MAPPINGS affect the predictions on the strength of strong UV, optical, and infrared emission lines. We find the dust-depleted radiation-pressure-dominated AGN model built with the latest nonlinear abundance sets and photoionization code MAPPINGS V are consistent with AGN observations across a broad range of wavelengths. We also assess new potential H ii-AGN separation diagrams in the optical and UV wavelengths.

A colourful analysis: Probing the eclipse of the black hole and central engine in NGC 6814 using X-ray colour–colour grids

ABSTRACT Eclipsing of the X-ray emitting region in active galactic nuclei (AGN) is a potentially powerful probe to examine the AGN environment and absorber properties. Here, we study the eclipse data from the 2016 XMM–Newton observation of NGC 6814 using a colour–colour analysis. Colours (i.e. hardness ratios) can provide the advantage of better time resolution over spectral analysis alone. Colour–colour grids are constructed to examine the effects of different parameters on the observed spectral variability during the eclipse. Consistent with previous spectral analysis, the variations are dominated by changes in the column density and covering fraction of the absorber. However, during maximum eclipse the behaviour of the absorber changes. Just after ingress, the eclipse is described by changes in column density and covering fraction, but prior to egress, the variations are dominated by changes in column density alone. Simulations are carried out to consider possible absorber geometries that might produce this behaviour. The behaviour is inconsistent with a single homogeneous cloud, but simulations suggest that multiple clouds, perhaps embedded in a highly ionized halo, could reproduce the results. In addition, we determine the orbital covering factor (fraction of orbital path-length) based on evidence of several eclipses in the 2016; 64-d Swift light curve. We estimate that ∼2–4 per cent of the orbit is covered by obscuring clouds and that the distribution of clouds is not isotropic.

Continuum Reverberation Mapping of Mrk 876 over Three Years with Remote Robotic Observatories

Continuum reverberation mapping probes the size scale of the optical continuum-emitting region in active galactic nuclei (AGN). Through 3 yr of multiwavelength photometric monitoring in the optical with robotic observatories, we perform continuum reverberation mapping on Mrk 876. All wave bands show large-amplitude variability and are well correlated. Slow variations in the light curves broaden the cross-correlation function (CCF) significantly, requiring detrending in order to robustly recover interband lags. We measure consistent interband lags using three techniques (CCF, JAVELIN, and PyROA), with a lag of around 13 days from u to z. These lags are longer than the expected radius of 12 days for the self-gravitating radius of the disk. The lags increase with wavelength roughly following λ 4/3, as would be expected from thin disk theory, but the lag normalization is approximately a factor of 3 longer than expected, as has also been observed in other AGN. The lag in the i band shows an excess that we attribute to variable Hα broad-line emission. A flux–flux analysis shows a variable spectrum that follows f ν ∝ λ −1/3, as expected for a disk, and an excess in the i band that also points to strong variable Hα emission in that band.

The role of grain size in active galactic nuclei torus dust models

Context. Active galactic nuclei (AGN) are surrounded by dust within the central parsecs. The dusty circumnuclear structures, referred to as the torus, are mainly heated by radiation from the AGN and emitted at infrared wavelengths, producing the emergent dust continuum and silicate features. Fits to the infrared spectra from the nuclear regions of AGN can place constraints on the dust properties, distribution, and geometry by comparison with models. However, none of the currently available models fully describe the observations of AGN currently available. Aims. Among the aspects least explored, here we focus on the role of dust grain size. We offer the community a new spectral energy distribution (SED) library which is based on the two-phase torus model developed before with the inclusion of the grain size as a model parameter, parameterized by the maximum grain size Psize or equivalently the mass-weighted average grain size ⟨P⟩. Methods. We created 691 200 SEDs using the SKIRT code, where the maximum grain size can vary within the range Psize = 0.01 − 10.0 μm (⟨P⟩ = 0.007 − 3.41 μm). We fit this new library and several existing libraries to a sample of 68 nearby and luminous AGN with Spitzer/IRS spectra dominated by AGN-heated dust. Results. We find that the GoMar23 model can adequately reproduce up to ∼85–88% of the spectra. The dust grain size parameter significantly improves the final fit in up to 90% of these spectra. Statistical tests indicate that the grain size is the third most important parameter in the fitting procedure (after the size and half opening angle of the torus). The requirement of a foreground extinction by our model is lower compared to purely clumpy models. We find that ∼41% of our sample requires that the maximum dust grain size is as large as Psize ∼ 10 μm (⟨P⟩∼3.41 μm). Nonetheless, we also remark that disk+wind and clumpy torus models are still required to reproduce the spectra of a nonnegligible fraction of objects, suggesting the need for several dust geometries to explain the infrared continuum of AGN. Conclusions. This work provides tentative evidence for dust grain growth in the proximity of the AGN.

Spectral and polarization properties of reflected X-ray emission from black-hole accretion discs for a distant observer: the lamp-post model

ABSTRACT Rebirth of X-ray polarimetric instruments will have a significant impact on our knowledge of compact accreting sources. The properties of inner-accreting regions of active galactic nuclei (AGNs) or X-ray binary systems, such as black-hole spin, their disc inclination and orientation, shape, and size of their corona, can be polarimetrically studied, parallelly to the well-known X-ray spectroscopic and timing techniques. In this work, we provide a new spectropolarimetric numerical estimate of X-rays in the lamp-post coronal model for a distant observer, including a polarized reflected radiation from the accretion disc. The local disc reflection was simulated using the codes titan and stokes and includes variable disc ionization as well as Monte Carlo treatment of Compton multiple scatterings. We introduce a relativistic code kynstokes based on our well-tested KY package that accounts for all relativistic effects on radiation near a black hole, apart from the returning radiation, and adds a possibility of polarized coronal emission. We study the spectrum, polarization degree and polarization angle at spatial infinity for various global system parameters and we demonstrate the difference at infinity, if analytical local reflection computations are used. We newly predict that in the hard X-rays the reflected component can be 25 per cent polarized and the total emission can be 9 per cent polarized in the most favourable, yet realistic configurations of radio-quiet AGNs. Thus, the relativistic disc reflection remains important for the interpretation of X-ray polarimetric observations.

General constraints on sources of high-energy cosmic rays from interaction losses

Sources of high-energy cosmic rays are presently unknown, but can be constrained in various ways. Some of these constraints can be graphically presented on the so-called Hillas diagram. Previous versions of this diagram determined the range of geometrical sizes and magnetic fields of potential astrophysical accelerators, taking into account geometrical criteria and radiation losses. In this work, we update the Hillas diagram for protons, taking into account the losses associated with the $p\ensuremath{\gamma}$ and photopair interactions, relating the allowed regions to the source electromagnetic luminosity. The strongest constraints are obtained for bright compact sources such as the central regions of active galactic nuclei.

Spiral arms in broad-line regions of active galactic nuclei

There is growing evidence that broad-line regions (BLRs) in active galactic nuclei (AGNs) have regular substructures, such as spiral arms. This is supported by the fact that the radii of BLRs measured by reverberation mapping (RM) observations are generally consistent with the self-gravitating regions of accretion disks. We showed in Paper I that the spiral arms excited by the gravitational instabilities in these regions may exist in some disk-like BLRs. Here, in the second paper of the series, we investigate the loosely wound spiral arms excited by gravitational instabilities in disk-like BLRs and present their observational characteristics. We solve the governing integro-differential equation by a matrix scheme. The emission-line profiles, velocity-delay maps, and velocity-resolved lags of the BLR spiral arms are calculated. We find that the spiral arms can explain some of the phenomena seen in observations: (1) different asymmetries in the emission-line profiles in the mean and rms spectra; (2) complex subfeatures (incomplete ellipse) in some velocity-delay maps, for example that of NGC 5548; and (3) the short timescales of the asymmetry changes in emission-line profiles (rms spectra). These features are attractive for modeling the observed line profiles and the properties of reverberation, and for revealing the details of the BLR geometry and kinematics.

Interactions between the Jet and Disk Wind in Nearby Radio-intermediate Quasar III Zw 2

Disk winds and jets are ubiquitous in active galactic nuclei (AGN), and how these two components interact remains an open question. We study the radio properties of the radio-intermediate quasar III Zw 2. We detect two jet knots, J1 and J2, on parsec scales that move at a mildly apparent superluminal speed of 1.35c. Two γ-ray flares were detected in III Zw 2 in 2009–2010, corresponding to the primary radio flare in late 2009 and the secondary radio flare in early 2010. The primary 2009 flare was found to be associated with the ejection of J2. The secondary 2010 flare occurred at a distance of ∼0.3 pc from the central engine, probably resulting from the collision of the jet with the accretion disk wind. The variability characteristics of III Zw 2 (periodic radio flares, unstable periodicity, multiple quasiperiodic signals and the possible harmonic relations between them) can be explained by the global instabilities of the accretion disk. These instabilities originating from the outer part of the warped disk propagate inward and can lead to modulation of the accretion rate and consequent jet ejection. At the same time, the wobbling of the outer disk may also lead to oscillations of the boundary between the disk wind and the jet tunnel, resulting in changes in the jet–wind collision site. Object III Zw 2 is one of the few cases observed with jet–wind interactions, and the study in this paper is of general interest for gaining insight into the dynamic processes in the nuclear regions of AGN.

Estimating reddening of the continuum and broad-line region of active galactic nuclei: the mean reddening of NGC 5548 and the size of the accretion disc

ABSTRACT We use seven different methods to estimate broad-line and continuum reddenings of NGC 5548. We investigate two possible reddening curves considered for active galactic nuclei (AGNs): the mean AGN reddening curve of Gaskell &amp; Benker (2007) which is relatively flat in the ultraviolet, and a curve that rises strongly into the ultraviolet like a Small Magellanic Cloud (SMC) reddening curve. We also consider a standard Milky Way curve. Regardless of the curve adopted, we find a total reddening ∼14 times greater than the small amount of reddening due to dust in the solar neighbourhood. The UV-to-optical ratios rule out a steep SMC-like reddening curve for NGC 5548. The Milky Way and Gaskell &amp; Benker curves give a mean reddening of E(B − V) = 0.25 ± 0.02. The four non-hydrogen-line reddening indicators imply that the intrinsic hydrogen line ratios are consistent with Baker–Menzel case B values. The unreddened optical to UV spectral energy distribution is consistent with the predicted distribution for an externally-illuminated accretion disc. The reddening we derive for NGC 5548 is typical of previous estimates for type-1 AGNs. Neglecting internal extinction leads to an underestimate of the luminosity at 1200 Å by a factor of seven. The size scale of the accretion disc has therefore been underestimated by a factor of ≈2.6. This is similar to the accretion disc size discrepancy found in the 2013 AGNSTORM campaign and thus supports the proposal by Gaskell (2017) that the accretion disc size discrepancy is primarily due to the neglect of reddening.

Rarefied Broad-line Regions in Active Galactic Nuclei: Anomalous Responses in Reverberation Mapping and Implications for Weak Emission-line Quasars

Reverberation mapping (RM) is a widely used method for probing the physics of broad-line regions (BLRs) in active galactic nuclei (AGNs). There is increasing preliminary evidence that the RM behaviors of broad emission lines are influenced by BLR densities; however, the influences have not been investigated systematically from a theoretical perspective. In this paper, we adopt a locally optimally emitting cloud model and use CLOUDY to obtain the one-dimensional transfer functions of the prominent UV and optical emission lines for different BLR densities. We find that the influences of BLR densities to RM behaviors mainly have three aspects. First, rarefied BLRs (with low gas densities) may show anomalous responses in RM observations. Their emission-line light curves inversely respond to the variations in continuum light curves, which may have been observed in some UV RM campaigns. Second, the different BLR densities in AGNs may result in correlations between the time lags and equivalent widths of emission lines, and may contribute to the scatters of the radius–luminosity relationships. Third, the variations in BLR densities may explain the changes in time lags in individual objects for different years. Some weak emission-line quasars are probably extreme cases of rarefied BLRs. We predict that their RM observations may show anomalous responses.

Excitation of Langmuir Waves in the Magnetospheres of AGN

In the paper we study the process of excitation of Langmuir waves in the magnetospheres of active galactic nuclei (AGN), by taking a general-relativistic expression of the GoldreichJulian density into account. We considered the linearised set of equations which describe dynamics of the studied mechanism: the Euler equation, the continuity equation and the Poisson equation. After solving the dispersion relation and obtaining the instability growth rate, we explored it versus several physical parameters: electron’s and proton’s relativistic factors and the mass and luminosity of AGN, which are supposed to be Kerr black holes. We showed that the parametric process of energy pumping into the Langmuir waves is very efficient and the electrostatic field’s amplitude will be exponentially amplifying, which might account for pair creation, particle acceleration and plasma heating processes in the nearby regions of AGN.

The High-ionization IR Fine Structure Lines as Bolometric Indicators of the AGN Power: Study of the Complete 12 μm AGN Sample

The high-ionization mid-IR lines, excited in the narrow-line regions of active galactic nuclei (AGN), barely affected by stellar excitation and dust extinction, trace the AGN bolometric power. We used the complete 12 μm sample of Seyfert galaxies, for which 100/116 objects have reliable 2–10 keV observations. The [Ne v] and [O iv] mid-IR lines linearly correlate with several AGN bolometric indicators (intrinsic 2–10 keV and observed 14–195 keV X-ray emission, compact nuclear 12 μm emission, [O iii] λ5007 Å line emission) in terms of both flux and luminosity. No evidence of systematic differences in these correlations is found among the Seyfert populations, including types 1 and 2 and Compton-thick and Compton-thin AGN. Nevertheless, we find that a sequence of high-to-low Eddington ratios together with strong-to-weak line excitation (traced by the [O iv]/[Ne ii] line ratio) encompasses from type 1 through type 2 AGN to low-ionization nuclear emission-line region galaxies, showing intrinsic differences in these three AGN populations. A positive correlation between the black hole accretion rate (BHAR) and the star formation rate (SFR) is found, but no correlation between the specific SFR and the ratio BHAR/M BH, simply reflecting the fact that the more massive a galaxy is, the more it is forming stars and feeding its central black hole. The JWST, just beginning operations, will allow large samples of AGN to be observed in these lines in the nearby universe (z < 0.9).

Mapping the circumnuclear regions of the Circinus galaxy with the Imaging X-ray Polarimetry Explorer

ABSTRACT We report on the Imaging X-ray Polarimetry Explorer (IXPE) observation of the closest and X-ray brightest Compton-thick active galactic nucleus (AGN), the Circinus galaxy. We find the source to be significantly polarized in the 2–6 keV band. From previous studies, the X-ray spectrum is known to be dominated by reflection components, both neutral (torus) and ionized (ionization cones). Our analysis indicates that the polarization degree is 28 ± 7 per cent (at 68 per cent confidence level) for the neutral reflector, with a polarization angle of 18° ± 5°, roughly perpendicular to the radio jet. The polarization of the ionized reflection is unconstrained. A comparison with Monte Carlo simulations of the polarization expected from the torus shows that the neutral reflector is consistent with being an equatorial torus with a half-opening angle of 45°–55°. This is the first X-ray polarization detection in a Seyfert galaxy, demonstrating the power of X-ray polarimetry in probing the geometry of the circumnuclear regions of AGNs, and confirming the basic predictions of standard Unification Models.