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 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 Probing Accretion Disks in AGN with Water Masers

1997 ◽  
Vol 163 ◽  
pp. 113-125
Author(s):  
Philip R. Maloney
Keyword(s):  
Accretion Disk ◽  
Accretion Disks ◽  
Galactic Nuclei ◽  
Quantitative Information ◽  
X Rays ◽  
Maser Emission ◽  
Radiative Efficiency ◽  
Physical Conditions ◽  
Water Masers ◽  
Water Maser

AbstractExtremely luminous extragalactic water masers – the so-called “megamasers”, with isotropic luminosities of tens to hundreds of solar luminosities – appear to be uniquely associated with active galactic nuclei. The recent survey of Braatz et al. indicates that 20% of Seyfert 2 galaxies have detectable water maser emission. Although originally suggested to arise in shocks, it now seems likely that the masers arise from the irradiation of high-pressure molecular gas by X-rays from the AGN. Quantitative modelling shows that the observed megamaser luminosities can plausibly be produced in this fashion. Both observational limits on the size scales and the high gas pressures required indicate that the water maser emission arises on very small scales, either in a circumnuclear “torus” or the accretion disk itself. In the best-studied case, NCG 4258, the masers are produced in a geometrically thin, warped accretion disk. The maser models can be used to derive quantitative information about the physical conditions in the disk, namely, the mass accretion rate, and therefore the radiative efficiency. I discuss the implications of water maser observations and models for the study of accretion disks and circumnuclear tori in AGN.

scholarly journals Cosmological Evolution of the Central Engine in High-Luminosity, High-Accretion Rate AGN

2014 ◽  
Vol 1 (1) ◽  
pp. 90-95
Author(s):  
Matteo Guainazzi
Keyword(s):  
Active Galactic Nuclei ◽  
Accretion Rate ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Cosmological Evolution ◽  
High Luminosity ◽  
X Ray ◽  
Central Engine ◽  
The Status ◽  
Multi Wavelength

In this paper I discuss the status of observational studies aiming at probing the cosmological evolution of the central engine in high-luminosity, high-accretion rate Active Galactic Nuclei (AGN). X-ray spectroscopic surveys, supported by extensive multi-wavelength coverage, indicate a remarkable invariance of the accretion disk plus corona system, and of their coupling up to redshifts z≈6. Furthermore, hard X-ray (<em>E</em> &gt;10 keV) surveys show that nearby Seyfert Galaxies share the same central engine notwithstanding their optical classication. These results suggest that the high-luminosity, high accretion rate quasar phase of AGN evolution is homogeneous over cosmological times.

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.

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

scholarly journals X-Ray Variability in Active Galactic Nuclei: Two Things That Everybody Should Know

1998 ◽  
Vol 11 (2) ◽  
pp. 804-807
Author(s):  
Karen M. Leighly
Keyword(s):  
Light Curve ◽  
Active Galactic Nuclei ◽  
Time Scales ◽  
Time Scale ◽  
Galactic Nuclei ◽  
X Rays ◽  
X Ray ◽  
Central Engine ◽  
Distinguishing Property

X-ray variability is a distinguishing property of Active Galactic Nuclei (AGN), and the energetics and time scales of the emission dictate that the X-rays must originate very close to the central engine. In this review I discuss two basic topics from AGN variability research. The first is the correlation of the variability time scale with the X-ray luminosity, and the second is the structure of the X-ray light curve. In each case, I first review the old results that have been known for approximately the last 10 years and then I discuss very new results which may force us to modify our ideas about the origin of AGN X-ray variability. Note that I am discussing the variability of non-blazar type AGN.

scholarly journals Compton Thick AGN

2013 ◽  
Vol 9 (S304) ◽  
pp. 112-118
Author(s):  
N. A. Levenson
Keyword(s):  
Active Galactic Nuclei ◽  
Geometric Distribution ◽  
Galactic Nuclei ◽  
Infrared Emission ◽  
Nuclear Activity ◽  
X Ray ◽  
Central Engine ◽  
Black Hole Growth ◽  
Hole Growth ◽  
X Ray Background

AbstractCompton thick active galactic nuclei (AGN), which are obscured by column density NH > 1.5 × 104 cm−2, can be difficult to identify. They are certainly cosmically significant, both in producing the observed cosmic X-ray background, and in providing a location where black hole growth is hidden from view. Here I review some recent results from surveys that provide indications of Compton thick AGN, considering X-ray, radio, and infrared selection techniques. I also offer a caution against using mid-infrared silicate features to measure line-of-sight obscuration to active galactic nuclei. Instead, these features better indicate the geometric distribution of dust that the central engine heats. I conclude that the outstanding problem of Compton thick AGN is not the cases where the obscuration is directly associated with the environment of the active nucleus itself, even in the most obscured examples. Instead, we still risk missing the completely buried AGN, which are obscured by large amounts of gas and dust over large solid angles. The solution to finding Compton thick AGN may be to begin the search based on infrared emission and star formation, and then select for nuclear activity.

scholarly journals Local AGN survey (LASr): I. Galaxy sample, infrared colour selection, and predictions for AGN within 100 Mpc

2020 ◽  
Vol 494 (2) ◽  
pp. 1784-1816
Author(s):  
D Asmus ◽  
C L Greenwell ◽  
P Gandhi ◽  
P G Boorman ◽  
J Aird ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galaxy Evolution ◽  
Galactic Nuclei ◽  
Wide Field ◽  
X Ray ◽  
Sky Survey ◽  
Galaxy Sample ◽  
Redshift Survey ◽  
Infrared Survey

ABSTRACT To answer major questions on supermassive black hole (SMBH) and galaxy evolution, a complete census of SMBH growth, i.e. active galactic nuclei (AGN), is required. Thanks to all-sky surveys by the Wide-field Infrared Survey Explorer (WISE) and the Spectrum-Roentgen-Gamma (SRG) missions, this task is now feasible in the nearby Universe. We present a new survey, the Local AGN Survey (LASr), with the goal of identifying AGN unbiased against obscuration and determining the intrinsic Compton-thick (CT) fraction. We construct the most complete all-sky galaxy sample within 100 Mpc ($90{{\ \rm per\ cent}}$ completeness for log (M*/M⊙) ∼ 9.4), four times deeper than the current reference, the Two Micron All-Sky Survey Redshift Survey (2MRS), which misses ${\sim}20{{\ \rm per\ cent}}$ of known luminous AGN. These 49k galaxies serve as parent sample for LASr, called LASr-GPS. It contains 4.3k already known AGN, $\ge 82{{\ \rm per\ cent}}$ of these are estimated to have $L^\mathrm{nuc}(12\, \mu \mathrm{m})\lt 10^{42.3}$ erg s−1, i.e. are low-luminosity AGN. As a first method for identifying Seyfert-like AGN, we use WISE-based infrared colours, finding 221 galaxies at $L^\mathrm{nuc}(12\, \mu \mathrm{m})\ge 10^{42.3}$ erg s−1 to host an AGN at $90{{\ \rm per\ cent}}$ reliability. This includes 61 new AGN candidates and implies an optical type 2 fraction of 50–71 per cent. We quantify the efficiency of this technique and estimate the total number of AGN with $L^\mathrm{int}(\rm {2-10\,keV})\ge 10^{42}$ erg s−1 in the volume to be $362^{+145}_{-116}$ ($8.6^{+3.5}_{-2.8}\, \times$ 10−5 Mpc−3). X-ray brightness estimates indicate the CT fraction to be 40–55 per cent to explain the Swift non-detections of the infrared selected objects. One third of the AGN within 100 Mpc remain to be identified, and we discuss the prospects for the eROSITA all-sky survey to detect them.

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