1. Andrea Comastri (INAF- Oss. Astr. Bologna)
The Cosmic X-ray Background Facts: a Nobel prize Fictions: The AGN synthesis models (?)
Andrea Comastri
(INAF- Oss. Astr. Bologna)
sabato 17 novembre 2018
GH2003 Workshop

2. Extragalactic Background Light
sabato 17 novembre 2018
GH2003 Workshop

3. The XRB spectrum: data (courtesy of R. Gilli) sabato 17 novembre 2018
GH2003 Workshop

4. The 2-10 keV XRB intensity Vecchi et al. (1999) Lumb et al. (2002)
(courtesy of R. Gilli)
Vecchi et al. (1999)
Lumb et al. (2002)
Kushino et al. (2002)
Tozzi et al. (2001)
Integrated flux
from resolved sources
sabato 17 novembre 2018
GH2003 Workshop

5. The origin of the cosmic XRB
Diffuse gas can contribute significantly to the cosmic XRB only below 2 keV (CMB argument, Wright et al. 1994; <10% Rosati et al. 2002) 
the hard XRB is due to
single sources
OBSCURED
AGN
Modificare o togliere
sabato 17 novembre 2018
GH2003 Workshop

6. XRB model formulae XRB spectrum Source spectrum
X ray luminosity function
(XLF)
Source counts
sabato 17 novembre 2018
GH2003 Workshop

7. Fit to the XRB spectrum
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GH2003 Workshop

8. SOURCE COUNTS
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GH2003 Workshop

9. Some “Facts”
60-70% of the XRB is made by sources around the knee of source counts (logfx=-14+-1)
The 2-10 keV spectrum is a flat power law (0.4  HEAO1-ASCA-BeppoSAX-XMM,…)
Absorption distribution logNH=21-24
Luminosity distribution logLx =
sabato 17 novembre 2018
GH2003 Workshop

10. Several “Fictions” Compton thick (log NH > 24) sources
Optical continuum and emission line properties of hard X-ray sources
Host galaxy properties
sabato 17 novembre 2018
GH2003 Workshop

11. Main model assumptions
The X-ray Luminosity Function and evolution of obscured AGN is unknown  TypeII=TypeI
The absorption distribution of obscured AGN is unknown (but the nearby Universe)
 XRB fit
Simple SED (power law + absorption log NH = 21-25)
sabato 17 novembre 2018
GH2003 Workshop

12. Observational constraints: N(NH), N(z)
Risaliti et al. (1999)
Observed in Seyfert 2s
Comastri
et al. (1995)
Fitted to the
XRB spectrum
Sy2/Sy1 ratio at z=0: (Maiolino & Rieke 1995)
sabato 17 novembre 2018
GH2003 Workshop

13. Observational constraints: need for QSO2
High Luminosity (logL(X)>
44) highly absorbed
(log(NH)=23+/-1) sources
are required to fit
bright counts
Compton Thick QSO
(logNH>24) are not
energetically important
sabato 17 novembre 2018
GH2003 Workshop

14. Hard counts (with/without Type 2 QSO)
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GH2003 Workshop

15. Hard Counts (Compton thick dominated)
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GH2003 Workshop

16. The deepest X-ray sky HDFN CDFS sabato 17 novembre 2018
GH2003 Workshop

17. The Deep X-ray Surveys
Survey X-ray observations Sensitivity/1e-16 N. Sources Reference
soft / hard
CDFS Msec Chandra ACIS-I / 4 * Giacconi et al.(2002)
500 ksec XMM
CDFN Msec Chandra ACIS-I / Alexander et al. (2003) ksec XMM
Lockman ksec XMM / ~ Hasinger et al. (2001)
300 ksec Chandra HRC
1.5 Msec ROSAT
260 ksec ASCA
Lynx ksec Chandra / Stern et al. (2002)
300 ksec XMM
SSA ksec Chandra / Mushotzky et al. (2000)
* extended to 0.2 / 2 by Campana et al. (2001) [see also Moretti et al. (2002)]
sabato 17 novembre 2018
GH2003 Workshop

18. Problems Redshift distribution Absorption distribution Quasar 2
sabato 17 novembre 2018
GH2003 Workshop

19. Redshift distribution in the Deep Surveys
CDFS + HDFN (Hasinger et al. 2003)
sabato 17 novembre 2018
GH2003 Workshop

20. Gandhi & Fabian 2003 Franceschini et al. 2002– link with IR?
Best fit to the peak, deficit at z>1 most likely
due to spectroscopic incompleteness…
BUT
sabato 17 novembre 2018
GH2003 Workshop

21. Abs/unabs ratio as a function of z
CDFN
CDFS+CDFN
CDFS
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GH2003 Workshop

22. Luminosity function: Cowie et al. 2003 Hasinger 2003 astro-ph/0301231
sabato 17 novembre 2018
GH2003 Workshop

23. Space density: Hasinger 2003 Cowie et al. 2003: rho_BH ~ 2x105
sabato 17 novembre 2018
GH2003 Workshop

24. X/O -------- fX/fopt > 10 Likely to be highly obscured
Undetected in the
R-band at R=24-25
(shallow), even
R>27-28 (deep)
Constant fraction
over a large range
of fluxes
Shallow surveys
pick-up brightest
sources  optical
identification is
possible
sabato 17 novembre 2018
GH2003 Workshop

25. 317 sources (Hellas2XMM + Lockman + CDFN + SSA13 -15 < logFx < -13.3 , 70% identified)
sabato 17 novembre 2018
GH2003 Workshop
Fiore et al astro-ph/

26. Redshift distribution (Opt +stat. ids)
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GH2003 Workshop

27. The evolution of number and luminosity densities (Fiore et al
The evolution of number and luminosity densities (Fiore et al. 2003, astro-ph/030556)
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GH2003 Workshop
rho_BH ~ 4-6x105

28. Average spectrum Tozzi et al. 2001 sabato 17 novembre 2018
GH2003 Workshop

29. 2a) Absorption distributions 2-10 keV
Chandra CDFN
XMM Hellas2Xmm
HEAO-1 Piccinotti et al.
ASCA Della Ceca et al.
XMM Piconcelli et al.
XMM Mainieri et al.
sabato 17 novembre 2018
GH2003 Workshop

30. 2b) Absorption distribution 5-10 keV
NH>1022
NH>1023
open: BeppoSAX HELLAS
filled: ASCA Sheep
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GH2003 Workshop

31. Absorption vs luminosity
CDFS
XMM Lockman Hole
QSO2s
From Mainieri et al. (2002)
sabato 17 novembre 2018
GH2003 Workshop

32. 3) Can we survive without QSO2 ?
QSO2 (luminous obscured sources) do exist…, but they are NOT luminous Seyfert 2.
EROs, high fx/fopt sources , broad lines quasars, ULIRGs…
X-ray and optical properties do not go hand in hand
Are they enough ? (see discussion)
sabato 17 novembre 2018
GH2003 Workshop

33. CDFS 202: QSO-2 detected Norman et al. 2002 LX ~ 1045 erg/s
NH ~ 1024cm-2
narrow high-excitation lines 6.4 keV
VLT-spectrum Chandra spectrum
1.4 keV = 6.4/(1+z)
Norman et al. 2002
sabato 17 novembre 2018
GH2003 Workshop

34. N(Z) predicted to peak around 1.5-2 Now it seems to peak at 0.7-1
Change the XLF parameters rather than assuming extremely fast evolution
N(NH)  HR vs. real spectra
N(NH)  lack of obscured sources at bright fluxes (30% obs vs. 50% expect)
Dependence of NH vs. z and/or luminosity ?
N(NH)+sharp drop of <alpha>  things are rapidly changing around logfx=-14 ?
sabato 17 novembre 2018
GH2003 Workshop

35. Conclusions ? Forget the unification scheme ?
Why the bull stop to moo at high luminosity ?
Space density and evolution of obscured sources ?
High energy spectrum ?
sabato 17 novembre 2018
GH2003 Workshop