X-ray Universe Symposium 2008 Granada, 27th May 2008
Cosmic evolution of AGN in several X-ray
bandsJacobo Ebrero
Instituto de Física de Cantabria (CSIC-UC)
X-ray Universe Symposium 2008 Granada, 27th May 2008
X-ray Universe Symposium 2008 Granada, 27th May 2008X-ray Universe Symposium 2008 Granada, 27th May 2008
OutlineOutline
• 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
IntroductionIntroduction
• 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
SamplesSamples• Soft (0.5 – 2 keV):
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
Overall sky coverage
XMS
CDF-S
RDS
RIXOS
RBS
X-ray Universe Symposium 2008 Granada, 27th May 2008
SamplesSamples
• Hard (2 – 10 keV):
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
Overall sky coverage
XMS
CDF-S
AMSS
X-ray Universe Symposium 2008 Granada, 27th May 2008
SamplesSamples
• Ultrahard (4.5 – 7.5 keV):
Survey NAGN Flux limit (cgs)
XMS 57 6.8 x 10-15
HBS 62 7.0 X 10-14
Overall sky coverage
XMS
HBS
X-ray Universe Symposium 2008 Granada, 27th May 2008
The NThe NHH function of Ultrahard sources 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.
Ebrero et al., 2008, in preparation
43 < log L4.5-7.5 < 43.75
X-ray Universe Symposium 2008 Granada, 27th May 2008
The X-ray luminosity functionThe 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: ResultsXLF: ResultsSoft (0.5-2 keV)Soft (0.5-2 keV)
X-ray Universe Symposium 2008 Granada, 27th May 2008
XLF: ResultsXLF: ResultsSoft (0.5-2 keV)Soft (0.5-2 keV)
Evolution in LX and redshift
present.
X-ray Universe Symposium 2008 Granada, 27th May 2008
XLF: ResultsXLF: ResultsHard (2-10 keV)Hard (2-10 keV)
X-ray Universe Symposium 2008 Granada, 27th May 2008
XLF: ResultsXLF: ResultsHard (2-10 keV)Hard (2-10 keV)
Evolution in LX and redshift
present.
X-ray Universe Symposium 2008 Granada, 27th May 2008
XLF: ResultsXLF: ResultsUltrahard (4.5-7.5 keV)Ultrahard (4.5-7.5 keV)
X-ray Universe Symposium 2008 Granada, 27th May 2008
XLF: ResultsXLF: ResultsUltrahard (4.5-7.5 keV)Ultrahard (4.5-7.5 keV)
Evolution in LX and redshift
present.
X-ray Universe Symposium 2008 Granada, 27th May 2008
XLF: ResultsXLF: ResultsComoving densityComoving density
Soft Hard
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: ResultsXLF: ResultsAccretion rate densityAccretion rate density
Soft Hard
UltrahardThe 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.
X-ray Universe Symposium 2008 Granada, 27th May 2008
SummarySummary
• 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 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.
