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Coevolution of black holes and
galaxies at high redshift
David M Alexander (Durham)
Some key issues in observational cosmology
The growth of black holes
The black-hole-host connection
Accretion Disk
Action: AGN activity
Black Hole
The role of environment?
Action: Star formation
SDSS optical quasar selection
identifies a small fraction
(~1-10%) of all AGNs
• Most AGNs are hidden at optical
wavelengths by dust and gas
• Host-galaxy dilution for lower-lum
X-ray surveys provide a more
complete census of AGN activity
X-rays: penetrate
high column densities
Difficulty in Constructing
a Complete AGN Census
X-ray Surveys: great steps towards a complete
census of AGN activity
Murray et al. (2005)
5 ks Chandra Bootes
High (quasar) luminosities
Moderate (Seyfert) luminosities
Low luminosities
Just CDF-N sources
2 Ms Chandra deep fields
Brandt et al. (2001), Alexander et al. (2003);
Giacconi et al. (2002); Luo et al. (2008)
• Detection of even low-luminosity AGN out to high redshift
• Need deeper spectroscopy (~70% complete) although photozs now getting
to good quality (e.g., Luo et al. 2010)
Particularly when allied with infrared identification
of the most heavily obscured AGNs
(1) Below detection limit: stacked X-ray data of IR-bright z~2 galaxies - hidden AGNs
Daddi et al. (2007); see also Fiore et al. (2008, 2009), Donley et al. (2008), and others
(2) Spectroscopic identification of individual
X-ray undetected luminous AGNs
Optical spectroscopy
IR spectra and SEDs
Alexander et al. (2008)
Steidel et al. (2002); Alexander et al. (2008)
Growth of black holes
Note: the definition of high redshift here is “only” z~1-4 - the identification of
large numbers of typical z>6 AGNs is challenging: only ~1 of z>6 AGN probably
per deep X-ray field and none reliably identified to date (see Gilli and Brandt talks)
Key result from X-ray surveys: AGN “cosmic
Ueda et al. (2003)
Hasinger et al. (2005)
Fiore et al. (2003)
Also Cowie et al. (2003); Barger et al. (2005);
La Franca et al. (2005); Aird et al. (2010) amongst others
Luminosity-dependent density evolution: high-luminosity AGNs (i.e., quasars) peaked at
higher redshifts than typical AGNs
Downsizing in “active” black-hole masses?
z~1: Babic et al. (2007)
Growing more rapidly now
Grew more rapidly in past
See also Ballo et al. (2007);
Alonso-Herrero et al. (2008)
z~0: Heckman et al. (2004)
In general this appears to be true - massive black holes (~108 solar masses) were growing
more rapidly at z~1 than in the present day, where smaller black holes (<107 solar
masses) were most active (Heckman et al. 2004; Goulding et al. 2010)
However, current observational constraints do not yet allow robust conclusions
Constraints at higher redshifts?
Limited constraints for highly selected sample
Model result (Soltan type approach)
z~2 ULIRGs vs SDSS
Alexander et al. (2008)
Marconi et al. (2004)
Higher-redshift constraints are key since many models predict rapid black-hole growth
at high redshift
But these are challenging due to lack of spec-zs of a complete sample and
black-hole-host galaxy mass relationship uncertainties: Brusa et al. (2009) similar z~2
constraints to Alexander et al. (2008) above
Tracing the black-hole-host mass relationship
Black-hole masses estimated with virial
technique (see Vestergaard talk)
Virial black-hole mass estimator:
Host-galaxy masses estimated from a
variety of techniques:
Host vel disp (em and abs lines), CO line
widths, absolute magnitudes, stellar
masses, and SED fitting
Merloni et al. (2010) result in COSMOS
Challenging to measure *both* black hole
and host mass without significant
uncertainties (see Wang talk)
But general concensus is for modest
evolution in MBH-MGAL ratio with redshift
- with relationship ~2-4x higher at z~2
and perhaps higher at z~2-6: factor ~4
based on Merloni et al. (2010)
Evolution perhaps only significant at
highest masses (>3x108 solar masses): see
Di Matteo talk (also Merloni et al. 2010)
See also McLure et al. (2006); Peng et al. (2006a,b); Shields et al. (2006); Woo et al. (2006, 2008);
Salviandar et al. (2007); Treu et al. (2007); Jahke et al. (2009); De Carli et al. (2010)
Similar result for rapidly evolving z~2 SMGs
Estimated MBH using virial mass estimator
for the few z~2 SMGs with broad lines
Estimated MGAL for the majority which
are host-galaxy dominated
SAM results, including feedback
Alexander et al. (2008); Hainline et al. (2010)
Not significant difference in average
MBH-MGALratio for various z~2 populations
But require constraints of more typical z~2-6
AGNs - want to test if there is a black-hole
mass dependence: need better spectroscopy,
imaging, and larger-area deep X-ray surveys
Lamastra et al. (2010)
Tentative evidence for feedback inducing blow out?
Collapsed IFU spectrum of z~2.07 SMG
~4-8 kpc extent of broad [OIII gas]
Broad (800 km/s) highvelocity (200-500 km/s)
[OIII] gas
Alexander et al. (2010); see Nesvadba et al. (2006,2007,2008) for results on rarer z~2 radio-loud AGNs
Di Matteo et al. (2005) simulation
What role does environment play?
A key laboratory of blackhole growth mechanisms:
a distant protocluster?
z=3.09 SSA22 protocluster
400ks Chandra
exposure of SSA22
Predicted to become a
massive Coma-like cluster
by the present day
The galaxy density is ~6x higher than the field already at z~3.09
Enhanced black-hole growth compared to the field
Lehmer et al. (2009a)
• The AGN activity per galaxy is larger
in the protocluster compared to the
field by a factor of 6.1+10.3 (enhanced at
the 95% confidence level) for AGNs
with LX > 3 Г— 1043 ergs sв€’1.
• Fraction of LAEs hosting AGNs
appears to be positively correlated with
the local LAE density (96% confidence
LX > 3 Г— 1043 ergs sв€’1
Lehmer et al. (2009b)
More massive black holes active at earlier times?
Host galaxies appear more massive in protocluster
• If the AGN fraction is larger in the
protocluster simply due to the
presence of more massive SMBHs,
then an average protocluster AGN
would be more luminous than an
average field AGN by the same factor
• For this to be the case, the SMBHs
would have to be ≈3−10 times more
massive in the protocluster than the
field: likely 108-109 solar masses
rather than 107-108 solar masses
Good agreement with that found
for a z=2.3 protocluster
(Digby-North et al. 2010)
Lehmer et al. (2009a)
Implication: the characteristic X-ray luminosity and “active” black-hole mass
appears to be a function of environment as well as redshift
And AGN fraction declines to lower redshifts
z~3.09 protocluster AGN fraction
• Significant drop (1-2 orders of
magnitude) in AGN fraction for similarly
overdense regions at z<1
• AGN activity has been “switched off” in
galaxy clusters/protoclusters since z~3
to z<1
AGN fraction in massive
galaxy clusters
• Need to trace this out from z~2-8 with
X-ray observations of more
protoclusters/overdense regions
Martini et al. (2009)
Require more constraints for more protoclusters, particularly at high redshift
Need deep X-ray observations of other overdense regions
Need wider area X-ray surveys to cover full range of environments
Has heating of the ICM tentatively started?
Geach et al. (2009)
LyпЃЎ images of some protocluster AGNs
AGN power
Potential heating mechanisms
QuickTimeв„ў and a
H.264 decompressor
are needed to see this picture.
Star-formation power
NASA press conference movie
~17% of extended LyпЃЎ emitters host luminous AGN in the z~3.09 protocluster;
AGNs are luminous enough to power the 10-100 kpc extended LyпЃЎ emission
• AGN cosmic downsizing possibly due to increase in active black hole
with redshift
• typical active black holes at z~1 are ~108 solar masses; more work
required to obtain reliable results at higher redshifts
• Evolution in black-hole-host mass relationship quite modest out to
z~2 - may be stronger out to higher redshift but current samples
are limited
• possible black-hole mass dependence - need constraints for typical
black holes
• possible evidence for z~2 feedback inducing blow out
• Environmental dependencies on black-hole growth: AGN fraction
increases in z~2-3 protoclusters than compared to field - probably
due to more massive “active” black holes
• AGN fraction significantly decreases compared to field at z<1 possibly due to gas depletion or heating
• AGN activity in z~3 protocluster luminous enough to power 10-100
kpc LyпЃЎ halos - early evidence for ICM heating?
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