X-ray Surveys of the Obscured Universe

Hasinger, G.

doi:10.1007/3-540-45553-1_53

Cited by 8 publications

(5 citation statements)

References 32 publications

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“…This might suggest that the central AGN is heavily obscured and we are observing the colours of the host galaxy. As shown by Hasinger (2000), one of these sources, which has been observed from radio to X-rays, shows a spectral energy distribution remarkably similar to that of the luminous absorbed AGN NGC 6240 (Vignati et al 1999).…”

Section: Discussionmentioning

confidence: 73%

Testing current synthesis models of the X-ray background

Gilli

Salvati

Hasinger

2001

A&A

226

285

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Abstract.We present synthesis models of the X-ray background where the available X-ray observational constraints are used to derive information on the AGN population properties. We show the need for luminous X-ray absorbed AGNs, the QSO2s, in reproducing the 2-10 keV source counts at relatively bright fluxes. We compare a model where the evolution of absorbed AGNs is faster than that of unabsorbed ones, with a standard model where absorbed and unabsorbed AGNs evolve at the same rate. It is found that an increase by a factor of ∼ 2 from z = 0 to z ∼ 1.3 in the ratio between absorbed and unabsorbed AGNs would provide a significant improvement in the data description. Finally, we make predictions on the AGNs to be observed in deep X-ray surveys which contain information on the AGN space density at high redshift.

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Section: Discussionmentioning

confidence: 73%

Testing current synthesis models of the X-ray background

Gilli

Salvati

Hasinger

2001

A&A

226

285

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“…To illustrate this, in Figure 36b, we have superposed the highly obscured local galaxy NGC 6240 (Hasinger 2000), which is often used as a template for absorbed AGNs. This template provides a fairly good description of the shape of the composite spectrum over the frequency range from the submillimeter to the UV.…”

Section: Bolometric Corrections By Spectral Typementioning

confidence: 99%

“…The dashed curves show the median value for the local hard X-ray-selected sample of Kuraszkiewicz et al (2003), which is primarily broad-line AGNs with a small admixture of intermediate-type Seyferts. In (b), the dot-dashed curve denotes the spectral energy distribution of the optically thick local galaxy NGC 6240 from Hasinger (2000), normalized to give a bolometric correction of 35. The solid curve denotes the same spectral energy distribution, normalized to give a bolometric correction of 85. lying well below the broad-line AGN values at the higher frequencies.…”

Section: Composite Spectral Energy Distributions By Hard X-ray Luminomentioning

confidence: 99%

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The Cosmic Evolution of Hard X-Ray-selected Active Galactic Nuclei

et al. 2005

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We use highly spectroscopically complete deep and wide-area Chandra surveys to determine the cosmic evolution of hard X-ray-selected active galactic nuclei (AGNs). For the deep fields, we supplement the spectroscopic redshifts with photometric redshifts to assess where the unidentified sources are likely to lie. We find that the median redshifts are fairly constant with X-ray flux at z $ 1.We classify the optical spectra and measure the FWHM line widths. Most of the broad-line AGNs show essentially no visible absorption in X-rays, whereas the sources without broad lines (FWHM < 2000 km s À1 ; ''optically narrow'' AGNs) show a wide range of absorbing column densities. We determine hard X-ray luminosity functions for all spectral types with L X ! 10 42 ergs s À1 and for broad-line AGNs alone. At z < 1:2, both are well described by pure luminosity evolution, with L * evolving as (1 þ z) 3:2AE0:8 for all spectral types and as (1 þ z) 3:0AE1:0 for broad-line AGNs alone. Thus, all AGNs drop in luminosity by almost an order of magnitude over this redshift range. We show that this observed drop is due to AGN downsizing rather than to an evolution in the accretion rates onto the supermassive black holes.We directly compare our broad-line AGN hard X-ray luminosity functions with the optical QSO luminosity functions and find that at the bright end they agree extremely well at all redshifts. However, the optical QSO luminosity functions do not probe faint enough to see the downturn in the broad-line AGN hard X-ray luminosity functions and even appear to be missing some sources at the lowest luminosities they probe.We find that broad-line AGNs dominate the number densities at the higher X-ray luminosities, while optically narrow AGNs dominate at the lower X-ray luminosities. We rule out galaxy dilution as a partial explanation for this effect by measuring the nuclear UV/optical properties of the Chandra sources using the Hubble Space Telescope Advanced Camera for Surveys GOODS-North data. The UV/optical nuclei of the optically narrow AGNs are much weaker than expected if the optically narrow AGNs were similar to the broad-line AGNs. We therefore postulate the need for a luminosity-dependent unified model. An alternative possibility is that the broad-line AGNs and the optically narrow AGNs are intrinsically different source populations. We cover both interpretations by constructing composite spectral energy distributions-including long-wavelength data from the mid-infrared to the submillimeterby spectral type and by X-ray luminosity. We use these spectral energy distributions to infer the bolometric corrections (from hard X-ray luminosities to bolometric luminosities) needed to map the accretion history.We determine the accreted supermassive black hole mass density for all spectral types and for broad-line AGNs alone, using the observed evolution of the hard X-ray energy density production rate and our inferred bolometric corrections. We find that only about one-half to one-quarter of the supermassive black hole mass ...

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“…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.…”

mentioning

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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X-ray Surveys of the Obscured Universe

Cited by 8 publications

References 32 publications

Testing current synthesis models of the X-ray background

Testing current synthesis models of the X-ray background

The Cosmic Evolution of Hard X-Ray-selected Active Galactic Nuclei

Supermassive black holes in deep multiwavelength surveys

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