scholarly journals The relationship between X-ray and optical absorbers in active galactic nuclei

2020 ◽  
Vol 493 (1) ◽  
pp. 930-939 ◽  
Author(s):  
Gunnar W Jaffarian ◽  
C Martin Gaskell
Keyword(s):  
Active Galactic Nuclei ◽  
Column Density ◽  
Scattered Light ◽  
Galactic Nuclei ◽  
Broad Line ◽  
Large Scatter ◽  
Standard Type ◽  
X Ray

ABSTRACT We present a large compilation of reddening estimates from broad-line Balmer decrements for active galactic nuclei (AGNs) with measured X-ray column densities. The median reddening is E(B − V) ≈ 0.77 ± 0.10 for type-1 to type-1.9 AGNs with reported column densities. This is notably higher than the median reddening of AGNs from the SDSS. We attribute this to the selection bias of the SDSS towards blue AGNs. For other AGNs, we find evidence of a publication bias against reporting low column densities. We find a significant correlation between NH and E(B − V) but with a large scatter of ±1 dex. On average, the X-ray columns are consistent with those predicted from E(B − V) for a solar neighbourhood dust-to-gas ratio. We argue that the large scatter of column densities and reddenings can be explained by X-ray column density variability. For AGNs with detectable broad-line regions (BLRs) that have undergone significant changes of Seyfert type (‘changing-look’ AGNs), we do not find any statistically significant differences in NH or E(B − V) compared to standard type-1 to type-1.9 AGNs. There is no evidence for any type-1 AGNs being Compton thick. We also analyse type-2 AGNs and find no significant correlation between NH and narrow-line region reddening. We find no evidence for a previously claimed anticorrelation. The median column density of LINERs is 22.68 ± 0.75 compared to a column density of 22.90 ± 0.28 for type-2 AGNs. We find the majority of low column density type-2 AGNs are LINERs, but NH is probably underestimated because of scattered light.

scholarly journals X-ray spectral and eclipsing model of the clumpy obscurer in active galactic nuclei

2019 ◽  
Vol 629 ◽  
pp. A16 ◽  
Author(s):  
Johannes Buchner ◽  
Murray Brightman ◽  
Kirpal Nandra ◽  
Robert Nikutta ◽  
Franz E. Bauer
Keyword(s):  
Active Galactic Nuclei ◽  
Column Density ◽  
Galactic Nuclei ◽  
Line Of Sight ◽  
Broad Line ◽  
X Ray ◽  
Line Region ◽  
Self Consistent ◽  
Multi Wavelength ◽  
Table Model

We present a unification model for a clumpy obscurer in active galactic nuclei (AGN) and investigate the properties of the resulting X-ray spectrum. Our model is constructed to reproduce the column density distribution of the AGN population and cloud eclipse events in terms of their angular sizes and frequency. We developed and released a generalised Monte Carlo X-ray radiative transfer code, XARS, to compute X-ray spectra of obscurer models. The geometry results in strong Compton scattering, causing soft photons to escape also along Compton-thick sight lines. This makes our model spectra very similar to our TORUS previous model. However, only if we introduce an additional Compton-thick reflector near the corona, we achieve good fits to NuSTAR spectra. This additional component in our model can be interpreted as part of the dust-free broad-line region, an inner wall or rim, or a warped disk. It cannot be attributed to a simple disk because the reflector must simultaneously block the line of sight to the corona and reflect its radiation. We release our model as an Xspec table model and present corresponding CLUMPY infrared spectra, paving the way for self-consistent multi-wavelength analyses.

scholarly journals X-ray absorption in INTEGRAL active galactic nuclei

2020 ◽  
Vol 639 ◽  
pp. A5
Author(s):  
A. Malizia ◽  
L. Bassani ◽  
J. B. Stephen ◽  
A. Bazzano ◽  
P. Ubertini
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Axial Ratio ◽  
Host Galaxy ◽  
Host Galaxies ◽  
X Ray ◽  
Line Region ◽  
Absorbing Material

In this work the INTEGRAL hard X-ray selected sample of active galactic nuclei (AGN) has been used to investigate the possible contribution of absorbing material distributed within the host galaxies to the total amount of NH measured in the X-ray band. We collected all the available axial ratio measurements of the galaxies hosting our AGN together with their morphological information and found that for our hard X-ray selected sample as well there is a deficit of edge-on galaxies hosting type 1 AGN. We estimate that in our hard X-ray selected sample there is a deficit of 24% (±5%) of type 1 AGN. Possible bias in redshift has been excluded, as we found the same effect in a well-determined range of z where the number and the distributions of the two classes are statistically the same. Our findings clearly indicate that material located in the host galaxy on scales of hundreds of parsecs and not aligned with the putative absorbing torus of the AGN can contribute to the total amount of column density. This galactic absorber could be large enough to hide the broad line region of some type 1 AGN, thus causing their classification as type 2 objects and giving rise to the deficiency of type 1 objects in edge-on galaxies.

scholarly journals Soft X-ray Variability and the Covering Fraction of Active Galactic Nuclei

1989 ◽  
Vol 134 ◽  
pp. 118-119
Author(s):  
Michael A. Strauss ◽  
Kenneth W. Wachter ◽  
Alexei V. Filippenko
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Line Of Sight ◽  
X Rays ◽  
Broad Line ◽  
X Ray ◽  
Broad Line Region ◽  
Line Region ◽  
Partial Covering

The variability of soft X-rays (0.2 – 2 keV) in some low-luminosity type 1 Seyferts may partly be due to an extrinsic mechanism: dense clouds of gas in the broad-line region, opaque to soft X-rays, move across our line of sight to the X-ray emitting portions of the accretion disk (Reichert, Mushotzky, and Holt 1986; Lawrence and Elvis 1982; Halpern 1984). As the clouds move, the covering fraction changes stochastically. Evidence for partial covering of the X-ray source in low-luminosity AGNs has been seen in soft X-ray spectra by Holt et al. (1980) and Reichert et al. (1985).

scholarly journals Chandra COSMOS Legacy Survey: Clustering dependence of Type 2 active galactic nuclei on host galaxy properties

2019 ◽  
Vol 632 ◽  
pp. A88
Author(s):  
V. Allevato ◽  
A. Viitanen ◽  
A. Finoguenov ◽  
F. Civano ◽  
H. Suh ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Large Scale ◽  
Formation Rate ◽  
Galactic Nuclei ◽  
Stellar Mass ◽  
Host Galaxy ◽  
X Ray ◽  
Normal Galaxies ◽  
Massive Halos

Aims. We perform clustering measurements of 800 X-ray selected Chandra COSMOS Legacy (CCL) Type 2 active galactic nuclei (AGN) with known spectroscopic redshift to probe the halo mass dependence on AGN host galaxy properties, such as galaxy stellar mass Mstar, star formation rate (SFR), and specific black hole accretion rate (BHAR; λBHAR) in the redshift range z = [0−3]. Methods. We split the sample of AGN with known spectroscopic redshits according to Mstar, SFR and λBHAR, while matching the distributions in terms of the other parameters, including redshift. We measured the projected two-point correlation function wp(rp) and modeled the clustering signal, for the different subsamples, with the two-halo term to derive the large-scale bias b and corresponding typical mass of the hosting halo. Results. We find no significant dependence of the large-scale bias and typical halo mass on galaxy stellar mass and specific BHAR for CCL Type 2 AGN at mean z ∼ 1, while a negative dependence on SFR is observed, i.e. lower SFR AGN reside in richer environment. Mock catalogs of AGN, matched to have the same X-ray luminosity, stellar mass, λBHAR, and SFR of CCL Type 2 AGN, almost reproduce the observed Mstar − Mh, λBHAR − Mh and SFR–Mh relations, when assuming a fraction of satellite AGN fAGNsat ∼ 0.15. This corresponds to a ratio of the probabilities of satellite to central AGN of being active Q ∼ 2. Mock matched normal galaxies follow a slightly steeper Mstar − Mh relation, in which low mass mock galaxies reside in less massive halos than mock AGN of similar mass. Moreover, matched mock normal galaxies are less biased than mock AGN with similar specific BHAR and SFR, at least for Q >  1.

scholarly journals Examining supernova events in Type 1 active galactic nuclei

2020 ◽  
Vol 495 (4) ◽  
pp. 4419-4429
Author(s):  
Beatriz Villarroel ◽  
Iñigo Imaz ◽  
Elisabeta Lusso ◽  
Sébastien Comerón ◽  
M Almudena Prieto ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Detection Rate ◽  
Statistical Study ◽  
Galactic Nuclei ◽  
Core Collapse ◽  
Late Type ◽  
Host Galaxies ◽  
Specific Kind

ABSTRACT A statistical study of intermediate Palomar Transient Factory supernovae (SNe) in Type 1 active galactic nuclei (AGNs) has shown a major deficit of supernovae around Type 1 AGN host galaxies, with respect to Type 2 AGN hosts. The aim of this work is to test whether there is any preference for Type 1 AGNs to host SN of a specific kind. Through the analysis of SN occurrence and their type (thermonuclear versus core-collapse), we can directly link the type of stars producing the SN events, thus this is an indirect way to study host galaxies in Type 1 AGNs. We examine the detection fractions of SNe, the host galaxies and compare the sample properties to typical host galaxies in the Open Supernova Catalog (OSC). The majority of the host galaxies in the AGN sample are late type, similar to typical galaxies hosting SN within the OSC. The findings are supportive of a deficiency of SNe near Type 1 AGNs, although we cannot with certainty assess the overall detection fractions of SNe in Type 1 AGNs relative to other SN host galaxies. We can state that Type 1 AGN has equal detection fractions of thermonuclear versus core-collapse SNe. However, we note the possibility of a higher detection rate of core-collapse supernovae in Type 1 AGN with insecure AGN classifications.

scholarly journals Powerful Water Masers in Active Galactic Nuclei

2002 ◽  
Vol 19 (4) ◽  
pp. 401-421 ◽  
Author(s):  
Philip R. Maloney
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Rotating Disk ◽  
Future Prospects ◽  
Maser Emission ◽  
X Ray ◽  
Central Engine ◽  
Water Masers ◽  
Water Maser

AbstractLuminous water maser emission in the 616–523 line at 22GHz has been detected from two dozen galaxies. In all cases the emission is confined to the nucleus and has been found only in AGN, in particular, in Type 2 Seyferts and LINERs. I argue that most of the observed megamaser sources are powered by X-ray irradiation of dense gas by the central engine. After briefly reviewing the physics of these X-Ray Dissociation Regions, I discuss in detail the observations of the maser disk in NGC 4258, its implications, and compare alternative models for the maser emission. I then discuss the observations of the other sources that have been imaged with VLBI to date, and how they do or do not fit into the framework of a thin, rotating disk, as in NGC 4258. Finally, I briefly discuss future prospects, especially the possibility of detecting other water maser transitions.

scholarly journals Changing-look active galactic nuclei: close binaries of supermassive black holes in action

2020 ◽  
Vol 643 ◽  
pp. L9
Author(s):  
Jian-Min Wang ◽  
Edi Bon
Keyword(s):  
Black Holes ◽  
Angular Momentum ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Extreme Case ◽  
Supermassive Black Holes ◽  
Close Binaries ◽  
Orbital Periods

Changing-look active galactic nuclei (CL-AGNs) as a new subpopulation challenge some fundamental physics of AGNs because the timescales of the phenomenon can hardly be reconciled with accretion disk models. In this Letter, we demonstrate the extreme case: close binaries of supermassive black holes (CB-SMBHs) with high eccentricities are able to trigger the CL transition through one orbit. In this scenario, binary black holes build up their own mini-disks by peeling gas off the inner edges of the circumbinary disk during the apastron phase, after which they tidally interact with the disks during the periastron phase to efficiently exchange angular momentum within one orbital period. For mini-disks rotating retrograde to the orbit, the tidal torque rapidly squeezes the tidal parts of the mini-disks into a much smaller radius, which rapidly results in higher accretion and short flares before the disks decline into type-2 AGNs. Prograde-rotation mini-disks gain angular momentum from the binary and rotate outward, which causes a rapid turn-off from type-1 to type-2. Turn-on occurs around the apastron phase. CB-SMBHs control cycle transitions between type-1 and type-2 with orbital periods but allow diverse properties in CL-AGN light curves.

Erratum: “Host Galaxies of Hard X‐Ray–Selected Type 2 Active Galactic Nuclei at Intermediate Redshifts” (ApJ, 647, 892 [2006])

2006 ◽  
Vol 653 (2) ◽  
pp. 1583-1583
Author(s):  
Gaku Kiuchi ◽  
Kouji Ohta ◽  
Masayuki Akiyama ◽  
Kentaro Aoki ◽  
Yoshihiro Ueda
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Host Galaxies ◽  
X Ray ◽  
Intermediate Redshifts
Sign in / Sign up

Export Citation Format

Share Document