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
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
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 4.5-7.5 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 0.5-2 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 4.5-7.5 keV band thus allowing us to
study their absorption properties.
X-ray Universe Symposium 2008
Granada, 27th May 2008
Samples
• Soft (0.5 – 2 keV):
RBS
RIXOS
Overall sky coverage
Survey
NAGN
Flux limit (cgs)
XMS
178
1.5 x 10-14
CDF-S
226
5.5 x 10-17
RIXOS
222
3.0 x 10-14
RDS
39
5.5 x 10-15
RBS
310
2.5 x 10-12
X-ray Universe Symposium 2008
RDS
CDF-S
XMS
Granada, 27th May 2008
Samples
AMSS
• Hard (2 – 10 keV):
Overall sky coverage
CDF-S
Survey
NAGN Flux limit (cgs)
XMS
120
3.3 x 10-14
CDF-S
236
4.5 x 10-16
AMSS
79
3.0 x 10-13
X-ray Universe Symposium 2008
XMS
Granada, 27th May 2008
Samples
HBS
• Ultrahard (4.5 – 7.5 keV):
XMS
Overall sky coverage
Survey
NAGN
Flux limit (cgs)
XMS
57
6.8 x 10-15
HBS
62
7.0 X 10-14
X-ray Universe Symposium 2008
Granada, 27th May 2008
The NH function of Ultrahard sources
We have used the joint XMS/HBS
sample in the 4.5-7.5 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 L4.5-7.5 < 43.75
Ebrero et al., 2008, in preparation
X-ray Universe Symposium 2008
Granada, 27th May 2008
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.
X-ray Universe Symposium 2008
Granada, 27th May 2008
XLF: Results
Soft (0.5-2 keV)
X-ray Universe Symposium 2008
Granada, 27th May 2008
XLF: Results
Soft (0.5-2 keV)
Evolution in LX and
redshift present.
X-ray Universe Symposium 2008
Granada, 27th May 2008
XLF: Results
Hard (2-10 keV)
X-ray Universe Symposium 2008
Granada, 27th May 2008
XLF: Results
Hard (2-10 keV)
Evolution in LX and
redshift present.
X-ray Universe Symposium 2008
Granada, 27th May 2008
XLF: Results
Ultrahard (4.5-7.5 keV)
X-ray Universe Symposium 2008
Granada, 27th May 2008
XLF: Results
Ultrahard (4.5-7.5 keV)
Evolution in LX and
redshift present.
X-ray Universe Symposium 2008
Granada, 27th May 2008
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.
X-ray Universe Symposium 2008
Granada, 27th May 2008
XLF: Results
Accretion rate density
Soft
The majority of the accretion
rate density in the Universe is
produced by low-luminosity AGN.
Hard
Ultrahard
High-luminosity AGN reach a
maximum in the accretion rate
density earlier than the less
luminous AGN.
X-ray Universe Symposium 2008
Granada, 27th May 2008
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 (4.5-7.5 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 Xray 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.
X-ray Universe Symposium 2008
Granada, 27th May 2008