1. The Space Density of Compton Thick AGN
Erin Bonning (Yale)
On behalf of Ezequiel Treister (ESO)
Meg Urry (Yale)
Shanil Virani (Yale)

2. 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.

3. 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.

4. 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

5. Exposure Map
Maximum depth: 2.2 Ms (inner contour)

6. INTEGRAL Flux Limit vs. Exposure Time
Flim t–1/2

7. 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.

8. 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.

9. 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

10. 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.

11. 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.

12. (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

13. 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

14. 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