1. Cosmological Evolution of Hard X-ray AGN Luminosity Function: Formation History of the SMBHs
Yoshihiro Ueda (ISAS)
Co-Is on construction of the HXLF:
Masayuki Akiyama (Subaru Telescope, NAOJ)
Kouji Ohta (Kyoto Univ.)
Takamitsu Miyaji (Carnegie Mellon Univ.)
Special thanks to ASCA extragalactic survey teams

2. Contents Optical identification of the ASCA MSS
(Akiyama et al ApJS, astro-ph/ )
Nature of Hard X-ray population at bright fluxes (fx > erg s-1 cm-2 in 2-10 keV)
Hard X-ray Luminosity Function (HXLF)
(U et al ApJ, astro-ph/ )
NH function and the HXLF
Population synthesis: Origin of the HXRB
Observational constraints on the SMBH formation: growth curve of SMBHs

3. Motivation AGN Luminosity Function: a goal of X-ray surveys
the most fundamental measure to understand the cosmological evolution of AGNs
How many AGNs in the universe (as a function of time)?
How supermassive black holes form?

4. The X-ray Background : 40 years mistery
Ginga spectrum of Seyfert II galaxies
(Awaki et al 1991)
Comastri et al. 1995

5. Importance of hard X-ray surveys
The XRB: all the integrated emission from acceting
supermassive black holes (SMBHs) in galaxies
To reveal the XRB origin is to reveal the evolution of AGNs i.e., the accretion history of SMBHs in the universe
Majority of AGNs are obscured !
from the XRB spectrum
Ginga spectra of Seyfert II galaxies (Awaki et al 1991)
column density distribution of neaby Seyferts II Galaxies (Risaliti et al 1999)
Surveys in hard band (above 2 keV) are crucial
to detect a major population of AGNs

6. The ASCA Medium Sensitivity Survey
(U. et al. 2001; Akiyama et al.2003)
Optical Identification of the AMSS-north sample
GIS 2-10 keV selected sample
Fx > 3x10-13 erg cm-2 s-1 (2-10 keV )
87 sources / 68 degree2
UH 2.2m, KPNO 2.1m, (Calar Alto 3.5m, SUBARU)
79 AGNs (3 BL Lacs), 7 Clusters, 1 star

7. Scattered nuclear light?
Optical Identification of the AMSSn sample (Akiyama, U, Ohta et al. 2003)
X-ray absorbed AGNs
(log NH >22)
(1) at z<0.6
do not show broad Hβline (x)
(2) at z>0.6
often show broad MgII, CIII, or Lyαlines
Scattered nuclear light?

8. Summary of optical properties of X-ray absorbed AGNs at Fx ~ 10-13
Low-redshift Low-luminosity AGNs
Classical Type Seyfert galaxies
Very hard sources: optically “normal” galaxies
(Watanabe et al 2002; cf. Mushotzky et al 2000 for Chandra)
High-redshift High-luminosity AGNs
Broad-lines are detected: X-ray type-II AGNs are not always optically type-II AGNs
We can not neglect the effect of scattered nuclear light
Av/NH values of AGNs are smaller than Galactic one ?
Next, I introduce two examples of absorbed AGNs, which can help the behavior of X-ray absorbed broad-line AGNs in high redshifts.

9. The Hard X-ray AGN Luminosity Function

10. Construction of the HXLF
We have performed statistical analysis from a combined AGN sample in the wide z-Lx range to derive
NH function (probability distribution function of absorption)
luminosity function (spatial number densities)
as a function of luminosity and redshift
Construction of a sample
1. selected in the hard X-ray band (E >2 keV)
2. covering a wide flux range
3. with high completeness
is crucial, in particular to constrain the evolution of type-II AGNs, major populations of the XRB.

11. Sample: 247 Hard-band Selected AGNs Total Completeness > 96 %
HEAO-1 A2 + MC-LASS
(total 49, Fx>1.7x10-11)
Shinozaki (Poster 77)
ASCA (142, Fx>2x10-14)
ALSS (30) Akiyama et al (2000)
AMSS(75+20) Akiyama et al (2003)
Deep surveys (12+5)
CDFN flux limited
(56, Fx>3.8x10-15)
Brandt et al (2001)
Barger et al (2002,2003)
X-ray type II (NH>1022)
Optical type II X

12. Analysis Utilize the maximum likelihood method
Search for a solution where the probability of finding the observed set of (L, z, NH) is maximized
Actual sensitivity is determined by count rate rather than “flux”, and hence depends on the spectral shape
Take into account detector response in each survey
Consider the spectrum of each source by referring to
HEAO-1: ASCA/XMM follow-up results
ASCA and CDFN: hardness ratio (assuming a photon index
of 1.9 with a reflection component)
Compton-thick AGNs are (and can be) neglected

13. Observed Luminosity Distribution
Optical Type II AGN
Observed fraction of type-II AGNs (both in X-ray and optical) decreases with the hard X-ray luminosity
X-ray Type II AGN
Total

14. Results: the NH Function
The probability distribution function of absorption column density of AGNs, as a function of Lx (and z)
Quantitative test of the “unified scheme”
All
Log Lx <43
43<Log Lx <44.5
Log Lx >44.5

15. Fraction of X-ray Absorbed AGNs
The fraction of X-ray absorbed AGNs (Log NH >22) decreases with the luminosity.
Its redshift dependence is not significant.
Modification of the simplest unified scheme is necessary.
claimed in e.g., Lawrence & Elvis (1982), Akiyama et al. (2000).
See also Steffen et al (2003)

16. The HXLF of All the Compton-thin AGNs (Type-I + Type-II)
Best described with a luminosity dependent density evolution (LDDE) where the cut-off redshift increases with the luminosity

17. The AGN Number Density as a Function of Redshift
Luminous AGNs has a peak (cutoff redshift) earlier than less luminous AGNs
Similar results:
see Miyaji et al (Poster 54)
Fiore et al (2003)
Related to the star forming activity?
e.g., Francheschini et al. (1999)
The evoluiton of the number density of high (low) luminosity AGNs is simlar to that of the star forming rate of early (late) type galaxies.
A strong link between formation of the SMBH and that of the spheroid component of galaxies.
~(1+z) 4 (z>zc)

18. Population Synthesis Model
Observed XRB spectrum
Integrated AGN emission from our HXLF and the absorption function (lower black) well reproduces the broad band XRB spectrum (blue) below 300 keV
High energy cutoff must be arround 500 keV in average
(red left: keV,
red right: 600 keV)
Presense of Compton-thick AGNs estimated by Risaliti et al (1999) is consistent with the XRB spectrum (upper black)
Reflection components are important
(green: no reflection)

19. Composition of the XRB AGNs with Log Lx ~ 43.8 or at z~0.6
most largely contribute to the 2-10 keV XRB

20. Comparison of the Quasar Optical LF with the HXLF Importance of Hard X-ray surveys for AGN astronomy
Data: Optical LF (Boyle et al 2000)
Line: Prediction from the HXLF

21. Formation history of the SMBHs: mass density
Total accreted mass (hence BH mass density) can be estimated by LF assuming the mass-to-energy conversion factor ε(Soltan 1982).
Compare with a local BH mass density estimated from the relation between BH mass and velocity dispersion to constrain ε.
Previous studies:
Fabian and Iwasawa (1999) , Elvis et al (2002):
use the XRB intensity assuming z=2 for all the XRB source
Yu and Tremaine (2002)
use the QSO optical LF from 2dF survey

22. The growth curve of SMBHs revealed from the HXLF
For ε=0.1 the total accreted mass estimated from the HXLF is marginally consistent with the present-day BH mass density from the SDSS, (2.9±0.6)x105 Mo Mpc-3 (Yu and Tremaine 2002), indicating that radiatively inefficiant accretion flow is not important for formation of SMBHs (F&I 1999).
Significant accretion has continued after z<1
From QSO OLF (Lx>1044)
With Compton-thick AGNs

23. Conclusion
The fraction of X-ray absorbed AGNs decreases with the intrinsic luminosity.
The HXLF of total AGNs is best described by a LDDE
where the cutoff redshift increases with the luminosity: the number density of luminous AGNs has a peak in earlier epochs than less luminous ones.
Purely “observation based” population synthesis model is constructed. Most of the XRB origin is now quantitatively resolved!
These results give:
Strong constraints on galaxy/QSO formation history
Trace of the accretion history of the universe of all the AGNs including obscured objects (i.e., RIAF is not important for SMBHs formation)