# Presentation: 516821

## Obscured Accretion, the X-ray Backgroundand the Evolution of AGN

- AC Fabian
- Institute of Astronomy
- Cambridge UK

- With help from P Gandhi & D Alexander
- and some slides from G Hasinger & J Tueller

- Gravity

- Nuclear fusion

## Hard spectral shape of XRB explained by intrinsic absorption in component sources (Setti & Woltjer 89)

- Model by Gandhi & Fabian 02; see also Madau et al; Comastri et al Gilli et al...

## MOST AGN emission must be absorbed!

- Fabian & Iwasawa 1999

- Typical quasars

## Absorbed AGN, particularly Compton-thick, are common

- 3 nearest AGN, NGC4945, Circinus galaxy and Centaurus A all have
-    NH>1023 cm-2, the first 2 being
-    Compton thick with NH>1.5x1024 cm-2.
- 3-5 times as many Seyfert II locally as Seyfert I AGN.
- What about quasars and distant AGN?

- Circinus; Matt et al

- Cen A; Smith et al

- Suzaku

## Absorbed AGN, particularly Compton-thick, are common

- 3 nearest AGN, NGC4945, Circinus galaxy and Centaurus A all have
-    NH>1023 cm-2, the first 2 being
-    Compton thick with NH>1.5x1024 cm-2.
- 3-5 times as many Seyfert II locally as Seyfert I AGN.
- What about quasars and distant AGN?

## Some distant/powerful Type II objects

- IRAS09104

- NGC6240

- 4C39.29

- Host cluster contribution

- Fe K line is due to absorption
- of harder X-ray emission from
- obscured quasar nucleus

- Hines et al 95

- MN 2005

- Gandhi, Fabian & Crawford 06

- IRAS15307

- Probably more complex geometry for obscuration than simple unification torus model
- Star-formation in surrounding gas helps keep it inflated so has high covering factor?

## Chandra and XMM-Newton Deep Surveys

- Point sources resolve most of the XRB in the 2-5 keV band
- Many faint sources are hard due to absorption; NH<2x1023cm-2.
- Mainly Lx<1044 erg s-1 peaking at z~0.8.

## Similar results on the bright end from ASCA surveys (Ueda et al 03) and HELLAS (Fiore et al)

- Ueda et al 2003

## Space/Luminosity density evolution

**Hasinger, Miyaji & Schmidt, 2005**

## Rise and fall of quasars and AGN

- X-ray background

- Slide from G Hasinger

## Type 2 fraction f(LX)

- Local Seyferts

- Type 2 fraction f(LX)

- Fraction of type-2‘s decreases with luminosity.
- Powerful AGN can „clean out“ their environment?

- Slide from
- G Hasinger

## Type 2 fraction f(z)

- No significant evolution in absorption fraction detected

## Constraining the NH distribution

-  still significant uncertainties and limited predictive power
- Need:
- identified samples of 10-30 keV sources
- & better determination of 20-40 keV background

- Also Dwelly et al. 2005

- Slide from G Hasinger

## Radiation pressure amplification factor over electron scattering

- Effective Eddington limit for
- obscuring gas is less than Edd limit for BH, so as BH grows it eventually blows away its shroud

- Fabian, Celotti & Erlund

## Accretion makes massive black holes

- Soltan 82

- Mean redshift

- Radiative efficiency η

- Original guesses (FI99) assume z~2, Κ~30 (appropriate for quasars) seemed OK if efficiency η~0.1.
- Rework by Elvis et al (02) suggested need η>0.15.
- But if ρ● ~3X105 Msun pc-3    (eg Yu & Tremaine 02) then a major problem requiring much higher η arises.
-    What (if anything) has gone wrong?

- h=0.75

## Modifications assuming most absorbed AGN are Seyferts not QSO

- Typical L<3X1044 erg s-1   Then Κ~15 and z~0.7
- This reduces ρ● to ~4-5x105      (OK?)
-       Fabian 03 Carnegie Conference
-     Marconi et al 04 MN
-     Ueda et al 03 ApJ 598 886
-     Shankar et al 04 MN
-     La Franca et al 06 ApJ

- Ranjan Vasudevan

## XMM PN+MOS

## Do the spectra of the resolved sources stack to make up the XRB spectrum?

- Worsley+04,05

## Resolved fraction

- Giaconni et al. 2002

- Worsley+04,05

## Missing XRB component

- Giaconni et al. 2002

## Properties of the missing AGN

- Giaconni et al. 2002

## Hickox & Markevitch 06 summed unresolved XRB in CDF-N and S

## Where are the sources?

** ****Missing sources need to be highly-obscured AGN, with N****H**** ~ 10****23**** – 10****24**** cm****-2**** at z ~ 0.5 - 1.5**
** ****Unobscured rest-frame 2-10 keV luminosities need to be less than ~ 5x10****43**** erg cm****-2**** s****-1**** or else they should have been already detected in CDFs**
** ****This suggests an obscured:unobscured ratio 3:1 similar to what we see in the local Universe**
**Stack X-rays from sources in deep HST and Spitzer fields...**

## Detection of X-ray emission

- CDF-N 0.5-2 keV

- CDF-N Z<22nd mag
- Smoothed image, log scale, 4-8 keV band

** ****Highly significant detection of X-ray emission when all sources included : ~8-30******** in each of 0.5-1, 1-2, 2-4 keV bands of CDF-N and S**
** ****Hard band detection less significant but 4.3******** and 2.8******** in 4-6 keV for the CDF-N and CDF-S (Z<~24mag)**

- GOODS

- Worsley+06

## 6-8 keV emission?

- CDF-N 0.5-2 keV

** ****Only see 1.2******** in CDF-N Z<23****rd**** and 1.9******** in CDF-S Z<22****nd****... but...**
** ****Background:source counts are 100:1 – even the entire missing XRB (40%) would only yield 2.1******** in the CDF-N and 1.4******** in the CDF-S**

## Chandra & Spitzer on CDFN

- D Alexander 06

## X-ray undetected AGNs in “weakest” class

**1896**

**L****X****~10****41**** erg/s BUT what about “dilution” factor from non-AGNs? To avoid individual X-ray detection, individual sources must have L****X****<10****42**** erg/s...****So AGNs must make up **_**10-100%**_** of the stacked sources, suggesting an ****X-ray undetected AGN source density of **_**~1,000-10,000 per sq.deg**_

**Average properties: <z>=0.85; <L****IR****>~10****11**** solars; <R>~23 mags:****statistically the same as the X-ray detected AGNs**

**Notes:**
Submm cosmology: Blain & Longair (1993) – K-correction also McMahon et al. (1994) for AGNs
Submm surveys probing starbursts: Blain et al. (1999)
Num counts (therefore ULIRG space density): Blain et al. (1999)
First AGNs: Isaak et al. (1994), Mcmahon et al. (1994), Dunlop et al. (1994)
RG 4C41.17 (Dunlop)
BR 1202-0725 (Isaak, : UKT14; McMahon: IRAM)
Cloverleaf (Barvainis)
PC 2047+0123 (z=3.8) and 8C 1435+635( z=4.26)  (Ivison 1995): IRAM 30m
Z=4.69 QSO (Omont et al. 1996); z>4 RQQs (Omont et al. 1996); mole gas in z=4.69 (Ohta et al. 1996; Omont et al. 1996)
UKT14 obs (Lawrence et al. 1991) – no RQQ detections
UKT14 obs (Highes et al. 1995) – IRAS RQQs
IRAM obs of z~1.2 (Omont et al. 2002); IRAM obs of z>3.8 (Omont et al. 2001); IRAM obs of z>4 (Omont et al. 1996); IRAM of SDSS (Carilli et al. 2000, 2001)

SCUBA obs of grav. Lensed QSOs (Barvainis & Ivison 2002)
SCUBA obs of z>4 QSOs and AGN cont. to submm (inc BLAGNs) (McMahon et al. 1999)
Isaak et al. (2002): SCUBA obs of z>4 AGNs
Priddey et al. (2003a, b) SCUBA obs of z~2 AGNs and z>5 AGNs

## MIR – Radio – X-rayhighly absorbed quasars

- Koekemoer+04 – X-ray sources with high        FX/Fopt.
- Donley+05 – Radio excess AGN   undetected in deep X-rays
- Polletta+06 – only 1/3 Spitzer CTk AGN detected in X-rays
- Treister+06 – Spitzer AGN number counts imply X-ray surveys may miss 1/2
- Barger+06 – AGN in deep radio survey may mean obsc AGN = 2 x unobsc AGN

- See also Martinez-Sansigre+06, Franceschini+05, Sturm+06, Barmby+06, Weedman+06

## ρ●    in units of 105 Msun Mpc-3 

- Unobscured  quasars and Seyferts    1.5-3
- Obscured Compton –thin Seyferts     2
- Compton-thick Seyferts                     0.5-1
- What of Compton thick quasars?
-    Need better direct estimate of ρ● locally before  can argue definitively for high η, although highly likely that it is 0.1 or higher, implying spinning BH

## Some remaining issues for XRB

- Hard shape of XRB spectrum
- Why so peaked?
- What determines the cutoff energy?
- Reflection high??

- 112 non-blazar AGN so far

- Markwardt, Barthelmy, Mushotzky,  Tueller

## AGN Evolution 

- N(H)

- Probable evolution of N(H)/L distribution with redshift- numbers are very uncertain
- z~1 is where ‘most’ of XRB originates
-  to get to Log L(x)=43 at z=1 requires a sensitivity of ~2x10-15 ergs/cm2/sec in 20-200 keV band
- NEED HARD X-RAY Imaging

- Slide from R Mushotzky

- Strong light bending can increase reflection

- Produced by P Gandhi using computations by J Malzac

## Summary

** ****X-ray Background resolved up to 6 keV. **
** ****We are missing >40% of XRB intensity above 6 keV and most of XRB above 10 keV**
** ****Missing fraction probably due to type II AGN**
**Spinning Kerr black holes needed**

## CDFN (D. Alexander)

## XMM-Newton Lockman Hole

** ****681 ks PN**
** ****858 ks MOS-1**
** ****878 ks MOS-2**
** ****314 arcmin****2**** central portion**
** ****156 sources in catalogue**
** ****0.2-12 keV photometry in 7 narrow bands**

## Chandra Deep Field North

** ****~2 Ms exposure**
** ****448 arcmin****2**
** ****503 detected sources**
** ****0.5-8 keV photometry in 5 bands**

- Alexander et al. 2003
- Brandt et al. 2001

## Chandra Deep Field South

** ****~1 Ms exposure**
** ****391 arcmin****2**
** ****326 detected sources**
** ****0.5-8 keV photometry in 5 bands**

- Giaconni et al. 2002

## Obscured Black-Hole Growth in Massive Galaxies

**Alexander et al.,  2005**

**Alexander et al., Nature, 2005**

**Stacked ~12Ms X-ray spectra: ~80% of the AGNs in massive SCUBA galaxies are obscured, some possibly Compton thick**

**The properties of the AGNs in SCUBA galaxies are consistent with an obscured black-hole growth phase prior to an unobscured quasar phase**

**AGNs in SCUBA galaxies**

## X-ray vs. Optical QSOs

- Hasinger, Miyaji & Schmidt, 2004

- High-z decline now seen in X-rays at all luminosities!
- Differences between X-ray and optical due to selection effects?

- Silverman et al., 2004 (Champ)
- Hasinger, Miyaji, Schmidt, 2004 (CDF/LH)

- Very large solid angle deep surveys are required to discover z>5 QSOs
- XMM/COSMOS
- Alternatively from other wavebands

- ~1/3 of XRB absorption-corrected energy density is in the ‘missing component,
- which plausibly are Compton-thick Seyferts at z~0.5-1

## Implications for AGN

- Most black hole growth is due to radiatively efficient accretion
- Most accreting gas releases most of its gravitational energy very close to the black hole
- Truncated discs, ADAFs, RIAFS etc only relevant for low accretion rates
- Massive wind outflows cannot take most of the power