1. Cosmic evolution of AGN in several X-ray bands
Jacobo Ebrero
Instituto de Física de Cantabria (CSIC-UC)
X-ray Universe Symposium 2008
Granada, 27th May 2008

2. Outline Introduction X-ray samples
The NH function of Ultrahard sources
The X-ray luminosity function
Results
Summary
X-ray Universe Symposium 2008
Granada, 27th May 2008

3. Introduction
We have computed the luminosity function of a combination of nearly completely identified AGN surveys in 3 different energy bands (0.5-2 keV, 2-10 keV and keV) up to z = 3.
The backbone of this study is the XMS survey, a flux-limited highly complete survey at medium fluxes. It is 96% complete in the keV band, and over 86% in the others.
We have combined XMS with other highly complete shallower and deeper surveys in order to obtain a wider LX-z plane coverage.
Detailed spectral information is available for most of the sources detected in the keV band thus allowing us to study their absorption properties.

4. Samples Soft (0.5 – 2 keV): Survey NAGN Flux limit (cgs)
XMS x 10-14
CDF-S x 10-17
RIXOS x 10-14
RDS x 10-15
RBS x 10-12
Overall sky coverage
XMS
CDF-S
RDS
RIXOS
RBS

5. Samples Hard (2 – 10 keV): Survey NAGN Flux limit (cgs)
Overall sky coverage
XMS
CDF-S
AMSS
Hard (2 – 10 keV):
Survey NAGN Flux limit (cgs)
XMS x 10-14
CDF-S x 10-16
AMSS x 10-13

6. Samples Ultrahard (4.5 – 7.5 keV): XMS 57 6.8 x 10-15
Overall sky coverage
XMS
HBS
Ultrahard (4.5 – 7.5 keV):
Survey NAGN Flux limit (cgs)
XMS x 10-15
HBS X 10-14

7. The NH function of Ultrahard sources
We have used the joint XMS/HBS sample in the keV band (119 identified AGN).
The NH function is a probability distribution for the absorption column density as a function of LX and redshift.
43 < log L < 43.75
Ebrero et al., 2008, in preparation

8. The X-ray luminosity function
We first calculate the binned XLF using the 1/Va method:
We perform a ML fit to an analytic model using all the available information in each source without binning.
We use a Luminosity-dependent Density Evolution (LDDE) model:
For the Ultrahard sources we use absorption-corrected data and we introduce the best-fit NH function when performing the fit.

9. XLF: Results
Soft (0.5-2 keV)

10. Evolution in LX and redshift present.
XLF: Results
Soft (0.5-2 keV)
Evolution in LX and redshift present.

11. XLF: Results
Hard (2-10 keV)

12. Evolution in LX and redshift present.
XLF: Results
Hard (2-10 keV)
Evolution in LX and redshift present.

13. XLF: Results
Ultrahard ( keV)

14. Evolution in LX and redshift present.
XLF: Results
Ultrahard ( keV)
Evolution in LX and redshift present.

15. XLF: Results ? Comoving density Hard Soft Ultrahard
High-luminosity AGNs reach a maximum in density earlier than the less luminous AGN.
Growth and formation more efficient for high-luminosity AGN. ?

16. Accretion rate density
XLF: Results
Accretion rate density
Soft
Hard
Ultrahard
The majority of the accretion rate density in the Universe is produced by low-luminosity AGN.
High-luminosity AGN reach a maximum in the accretion rate density earlier than the less luminous AGN.

17. Summary
We have used the XMS survey along with other highly complete shallower and deeper surveys to study the cosmic evolution of AGN in three energy bands: Soft (0.5-2 keV), Hard (2-10 keV) and Ultrahard ( keV). The XLF has been computed by ML fitting to an analytic model (LDDE).
We have modelled the intrinsic absorption of the Ultrahard sample (NH function). We found that the fraction of absorbed AGN depends on the X-ray luminosity but not on redshift.
High-luminosity AGN grow and feed more efficiently in the early stages of the Universe than the less luminous AGN, and are fully formed at redshifts ~1.5-2.
The evolution of AGN along cosmic time is therefore not caused by changes in the absorption environment but by intrinsic variations in the accretion rate at different epochs of the Universe.