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The Space Density of Compton Thick AGN
Erin Bonning (Yale) On behalf of Ezequiel Treister (ESO) Meg Urry (Yale) Shanil Virani (Yale)
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Compton Thick AGN Defined as obscured sources with NH>1024 cm-2.
Very hard to find (even in X-rays). Observed locally and needed to explain the X-ray background. Number density highly uncertain. High energy (E>10 keV) observations are required to find them. There is a population of AGN that was completely missed in all previous studies. Those are the most obscured sources. So obscured that are not detected even in X-rays. Those are the CT AGN. Even though we don’t know the exact density of these sources, they are required in large numbers by XRB synthesis models and are observed locally.
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INTEGRAL Survey 2 Msec (expected 3 Msec by summer 2008) Deepest extragalactic INTEGRAL survey XMM-LSS field Flux limit: ~4x10-12 ergs cm-2 s-1 (20-40 keV) Area: ~1,000 deg2 10 Sources, ~2 Compton thick AGN In order to study directly this population, at least at low redshifts, three years ago we started a deep survey at high energies with INTEGRAL.
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INTEGRAL Mosaic (2.2 Ms) Significance Image, 20-50 keV MCG-02-08-014
These are the first results. We found a total of 10 sources, including the “famous” CT AGN NGC1068. But, we recently got a nice surprise when we got the first 2 Mseconds of data. We detected in INTEGRAL a source not detected in ROSAT, MCG Significance Image, keV
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Exposure Map Maximum depth: 2.2 Ms (inner contour)
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INTEGRAL Flux Limit vs. Exposure Time
Flim t–1/2
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Space Density of CT AGN X-ray background does not constrain density of CT AGN We can also construct the logN-logS for CT AGN only. Here we found that the CT AGN fraction is ~4x lower than what expected by models. This is because the XRB does not constrain the density of CT AGN.
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CT AGN and the XRB XRB Intensity HEAO-1 Original Treister & Urry, 2005
Gilli et al. 2007 Treister & Urry, 2005 Different models assumed different normalizations for the XRB, but now thanks to the recent INTEGRAL and Swift results, it is clear that the original HEAO-1 intensity, with a 10% uncertainty was correct, as assumed by the models of Gilli et al published this year.
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CT AGN and the XRB XRB Intensity HEAO-1 Original Treister & Urry, 2005
Gilli et al. 2007 Treister & Urry, 2005 Most likely solution However, now we can constrain the density of CT AGN directly from the INTEGRAL observations, finding that the most likely solution has a CT AGN fraction ~4x lower than previously expected. CT AGN Space Density
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X-ray Background Synthesis
So, we can now construct XRB population synthesis models completely constrained by observations, finding that most of the emission comes from sources with relatively low luminosities, 10^43-44 which corresponds to bright seyferts or faint quasars.
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INTEGRAL AGN logN-logS
Beckmann et al. 2006 In order to compare our results with the expectations from XRB models, The first tool for that is the logN-logS plot. Here we show it including the results from large area surveys (almost all-sky) at these energies. In general there is a good agreement.
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(Near) Future AGN logN-logS
In order to compare our results with the expectations from XRB models, The first tool for that is the logN-logS plot. Here we show it including the results from large area surveys (almost all-sky) at these energies. In general there is a good agreement. 14
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Summary INTEGRAL (& Swift) give important constraints on Compton Thick AGN (at z=0) X-ray “background” synthesis OK (but XRBG spectrum somewhat uncertain) Reflection component normalization ~ 1 (agrees with spectra) Deeper surveys probe evolution to z~1
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INTEGRAL Mosaic (2.2 Ms) Significance Image, 20-50 keV
These are the first results. We found a total of 10 sources, including the “famous” CT AGN NGC1068. But, we recently got a nice surprise when we got the first 2 Mseconds of data. We detected in INTEGRAL a source not detected in ROSAT, MCG Significance Image, keV
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