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 The Hard X‐Ray Spectrum as a Probe for Black Hole Growth in Radio‐Quiet Active Galactic Nuclei

2008 ◽  
Vol 682 (1) ◽  
pp. 81-93 ◽  
Author(s):  
Ohad Shemmer ◽  
W. N. Brandt ◽  
Hagai Netzer ◽  
Roberto Maiolino ◽  
Shai Kaspi
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
X Ray ◽  
Black Hole Growth ◽  
Hole Growth

scholarly journals Variable Sources in Active Galactic Nuclei

1999 ◽  
Vol 194 ◽  
pp. 384-388
Author(s):  
V. A. Hagen-Thorn ◽  
S. G. Marchenko ◽  
V. A. Yakovleva ◽  
A. V. Hagen-Thorn
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Nuclear Activity ◽  
X Ray ◽  
Central Engine

The problem of the activity of extragalactic objects is one of the main problems of current astrophysics. There are many manifestations of activity but the photometric and polarimetric variability in IR, optical, UV and X-ray regions is probably one of the most important. The sources responsible for the variability are placed in the nearest neighbourhood of a central engine. Clarifying the nature of these sources might give a tool to the solution of the problem of nuclear activity in general.

scholarly journals The Relation between Mid-Infrared Emission and Black Hole Mass in Active Galactic Nuclei: A Direct Way to Probe Black Hole Growth?

2002 ◽  
Vol 571 (1) ◽  
pp. L1-L5 ◽  
Author(s):  
Almudena Alonso-Herrero ◽  
Valentin D. Ivanov ◽  
Ray Jayawardhana ◽  
Takashi Hosokawa
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Infrared Emission ◽  
Black Hole Mass ◽  
Mid Infrared ◽  
Black Hole Growth ◽  
Hole Growth

Active galactic nuclei make the cosmic X-ray background

1993 ◽  
Vol 414 ◽  
pp. L81 ◽  
Author(s):  
Andrzej A. Zdziarski ◽  
Piotr T. Zycki ◽  
Julian H. Krolik
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
X Ray ◽  
X Ray Background

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 The Multiwavelength AGN Population and the X-ray Background

2013 ◽  
Vol 9 (S304) ◽  
pp. 188-194
Author(s):  
Ezequiel Treister ◽  
Claudia M. Urry ◽  
Kevin Schawinski ◽  
Brooke D. Simmons ◽  
Priyamvada Natarajan ◽  
...  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Mass Density ◽  
Large Fraction ◽  
Supermassive Black Holes ◽  
X Rays ◽  
X Ray ◽  
Black Hole Growth ◽  
Hole Growth ◽  
X Ray Background

AbstractIn order to fully understand galaxy formation we need to know when in the cosmic history are supermassive black holes (SMBHs) growing more intensively, in what type of galaxies this growth is happening and what fraction of these sources are invisible at most wavelengths due to obscuration. Active Galactic Nuclei (AGN) population synthesis models that can explain the spectral shape and intensity of the cosmic X-ray background (CXRB) indicate that most of the SMBH growth occurs in moderate-luminosity (LX~ 1044 erg/s) sources (Seyfert-type AGN), at z~ 0.5−1 and in heavily obscured but Compton-thin, NH~ 1023cm−2, systems. However, this is not the complete history, as a large fraction of black hole growth does not emit significantly in X-rays either due to obscuration, intrinsic low luminosities or large distances. The integrated intensity at high energies indicates that a significant fraction of the total black hole growth, 22%, occurs in heavily-obscured systems that are not individually detected in even the deepest X-ray observations. We further investigate the AGN triggering mechanism as a function of bolometric luminosity, finding evidence for a strong connection between significant black hole growth events and major galaxy mergers from z~ 0 to z~ 3, while less spectacular but longer accretion episodes are most likely due to other (stochastic) processes. AGN activity triggered by major galaxies is responsible for ~60% of the total black hole growth. Finally, we constrain the total accreted mass density in supermassive black holes at z > 6, inferred via the upper limit derived from the integrated X-ray emission from a sample of photometrically selected galaxy candidates. We estimate an accreted mass density <1000 M⊙Mpc−3 at z~ 6, significantly lower than the previous predictions from some existing models of early black hole growth and earlier prior observations.

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