Unified Models for Active Galactic Nuclei and Quasars

Antonucci, Robert

doi:10.1146/annurev.aa.31.090193.002353

Cited by 3,330 publications

(883 citation statements)

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“…We believe these blank-spectrum objects are also type-2 quasars with z > ∼ 1.4 and there is no compelling argument against them having z > ∼ 2 since the Lyman-α line can easily be extinguished if the host galaxy is dusty on large (kpc) scales. We are probably seeing two types of type-2: the objects with narrow emission lines are obscured by the torus [3] , while the blank-spectrum objects are probably obscured by a starbursting host galaxy and we are seeing the coeval growth of supermassive black hole and host galaxy. Growing supermassive black holes embedded in a starburst have been found at z ∼ 2 from X-ray measurements of submillimetre-selected galaxies [21] .…”

mentioning

confidence: 99%

The obscuration by dust of most of the growth of supermassive black holes

Martínez‐Sansigre

Rawlings

Lacy

et al. 2005

Nature

176

225

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Supermassive black holes underwent periods of exponential growth during which we seem them as quasars in the distant Universe. The summed emission from these quasars generates the cosmic X-ray background, the spectrum of which has been used to argue that most black-hole growth is obscured [1−2] .There are clear examples of obscured black-hole growth in the form of 'type-2' quasars [3−5] , but their numbers are fewer than expected from modelling of the X-ray background. Here we report on the direct detection of a population of distant type-2 quasars which is at least comparable in size to the well-known unobscured type-1 population. We selected objects that have mid-infrared and radio emissions characteristic of quasars, but which are faint at near-infrared and optical wavelengths. This population is responsible for most of the black hole growth in the young Universe and, throughout cosmic history, black-hole growth occurs in the dusty, gas-rich centres of active galaxies.The population of unobscured type-1 quasars is now well understood out to redshift z ∼ 2 by virtue of optical surveys [6] which provide direct measurements around the "break" in the luminosity function where the quasar population outputs most of its luminosity density.Current understanding of the obscured type-2 quasar population is far less complete.Examples of type-2 quasars have, for many years, been confined mainly to radio-selected samples. Radio emission is unaffected by dust and, at low frequencies, is not strongly dependent on viewing angle so the simplest interpretation of optical spectroscopic follow-up of

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mentioning

confidence: 99%

The obscuration by dust of most of the growth of supermassive black holes

Martínez‐Sansigre

Rawlings

Lacy

et al. 2005

Nature

176

225

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“…The lack of high-ionization lines and low [Ne iii]/[Ne ii] ratio can be actually reconciled with the presence of a deeply obscured AGN by allowing for a peculiar geometry of the gaseous/dusty absorber. Indeed, a large covering factor of the putative torus predicted by AGN unification models [22] can even prevent the formation of the narrow-line region and the production of high-ionization species. The geometrical properties of the absorber in a ULIRG are likely much more complicated, and a cocoon-like structure can be reasonably expected.…”

Section: Spitzer/irs Spectroscopymentioning

confidence: 99%

The Circumnuclear Environment of IRAS 20551-4250: A Case Study of AGN/Starburst Connection forJWST

Sani

Nardini

2012

Advances in Astronomy

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We present a general review of the current knowledge of IRAS 20551-4250 and its circumnuclear environment. This Ultraluminous Infrared Galaxy is one of the most puzzling sources of its class in the nearby Universe: the near-IR spectrum is typical of a galaxy experiencing a very intense starburst, but a highly obscured active nucleus is identified beyond ∼5 μm and possibly dominates the mid-IR energy output of the system. At longer wavelengths star formation is again the main driver of the global spectral shape and features. We interpret all the available IR diagnostics in the framework of simultaneous black hole growth and star formation and discuss the key properties that make this source an ideal laboratory for the forthcoming James Webb Space Telescope.

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“…First, a large body of evidence suggests that local AGN have geometries that are not spherically symmetric, and that different aspect angles present markedly different observed characteristics; this is referred to as AGN unification (Antonucci 1993;Urry & Padovani 1995). Second, AGN are more common at high redshift (z ∼ 2 − 3), where the average star formation rate is higher and thus it is even more likely that gas and dust surround the galaxy nucleus than at z ∼ 0.…”

Section: Cosmic Growth Of Black Holes and Galaxiesmentioning

confidence: 99%

Supermassive black holes in deep multiwavelength surveys

Urry¹,

Treister²

2011

Black Holes

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In recent years deep X-ray and infrared surveys have provided an efficient way to find accreting supermassive black holes, otherwise known as active galactic nuclei (AGN), in the young universe. Such surveys can, unlike optical surveys, find AGN obscured by high column densities of gas and dust. In those cases, deep optical data show only the host galaxy, which can then be studied in greater detail than in unobscured AGN. Some years ago the hard spectrum of the Xray "background" suggested that most AGN were obscured. Now GOODS, MUSYC, COSMOS and other surveys have confirmed this picture and given important quantitative constraints on AGN demographics. Specifically, we show that most AGN are obscured at all redshifts and the amount of obscuration depends on both luminosity and redshift, at least out to redshift z ∼ 2, the epoch of substantial black holes and galaxy growth. Larger-area deep infrared and hard X-ray surveys will be needed to reach higher redshifts and to probe fully the co-evolution of galaxies and black holes. Cosmic Growth of Black Holes and GalaxiesAbundant evidence indicates that the growth of a supermassive black hole is closely tied to the formation and evolution of the surrounding galaxy. The energy released from accretion onto the black hole affects star formation in the galaxy, probably limiting growth at the high-and low-mass ends, and of course the distribution and angular momentum of matter in the galaxy governs the amount of matter accumulated by the black hole (Silk & Rees 1998;King 2005;Rovilos et al. 2007). Emergent energy from accretion is also a factor in understanding ionization and radiation backgrounds (Hasinger 2000;Lawrence 2001). Understanding the growth history of these black holes is therefore critical to understanding the global evolution of structure in the Universe.Yet the demographics of supermassive black holes remain elusive. The largest samples of quasars and Active Galactic Nuclei (AGN), by which we mean supermassive black holes in a high accretion-rate phase †, have been found through optical selection (e.g., the Sloan Digital Sky Survey quasar sample; Schneider et al. 2002Schneider et al. , 2007, but, at least locally, these are not representative of the larger AGN population. Instead we need surveys less biased against obscured AGN.There are three reasons to suspect that most AGN are obscured by large column densities of gas and dust. First, a large body of evidence suggests that local AGN have geometries that are not spherically symmetric, and that different aspect angles present markedly different observed characteristics; this is referred to as AGN unification (Antonucci 1993;Urry & Padovani 1995). Second, AGN are more common at high redshift (z ∼ 2 − 3), where the average star formation rate is higher and thus it is even more likely that gas and dust surround the galaxy nucleus than at z ∼ 0. Third, and most important, obscured AGN are required to explain the shape of the X-ray "background" radiation.The X-ray "background" is actually the superposition of ind...

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Unified Models for Active Galactic Nuclei and Quasars

Cited by 3,330 publications

References 1 publication

The obscuration by dust of most of the growth of supermassive black holes

The obscuration by dust of most of the growth of supermassive black holes

The Circumnuclear Environment of IRAS 20551-4250: A Case Study of AGN/Starburst Connection forJWST

Supermassive black holes in deep multiwavelength surveys

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