Demography how many AGN in the sky? - number counts of normal galaxies radio sources optically selected AGN X-ray selected AGN how many AGN per cubic Mpc? - Luminosity functions and their evolution normal galaxies optically selected AGN X-ray selected AGN QSO: probes of high z Univer - Supermassive black hole volume density
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Demography how many AGN in the sky? - number counts of normal galaxies radio sources optically selected AGN X-ray selected AGN how many AGN per cubic Mpc?
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Demography
how many AGN in the sky?
- number counts of normal galaxies radio sources optically selected AGN X-ray selected AGN
how many AGN per cubic Mpc?
- Luminosity functions and their evolution normal galaxies optically selected AGN X-ray selected AGN QSO: probes of high z Universe - Supermassive black hole volume density
Number counts
Flux limited sample: all sources in a given region of the sky with flux > thansome detection limit Flim.
• Consider a population of objects with the same L • Assume Euclidean space
Number countsTest of evolution of a source population (e.g. radio sources). Distances of individual sources are not required, just fluxes or magnitudes: the number of objects increases by a factor of 100.6=4 with each magnitude.So, for a constant space density, 80% of the sample will be within 1 mag from the survey detection limit.
If the sources have some distribution in L:
Problems with the derivation of the number counts
• Completeness of the samples.
• Eddington bias: random error on mag measurements can alter the number counts. Since the logN-logFlim are steep, there are more sources at faint fluxes, so random errors tend to increase the differential number counts. If the tipical error is of 0.3 mag near the flux limit, than the correction is 15%.
• Variability.
• Internal absorption affects “color” selection.
• SED, ‘K-correction’, redshift dependence of the flux (magnitude).
Radio sources number counts
Galaxy number counts
Optically selected AGN number counts
Z<2.2B=22.5 100 deg-2
B=19.5 10 deg-2
z>2.2B=22.5 50 deg-2
B=19.5 1 deg-2
B-R=0.5
X-ray AGN number counts
<X/O> OUV sel. AGN=0.3
R=22 ==> 310-15 1000deg-2 R=19 ==> 510-14 25deg-2
The surface density of X-ray selected AGNis 2-10 times higher than OUV selected AGN
The V/Vmax testMarteen Schmidt (1968) developed a test for evolution not sensitive tothe completeness of the sample.Suppose we detect a source of luminosity L and flux F >Flim at a distance
r in Euclidean space:
If we consider a sample of sources distributed uniformly, we expect that half will be found in the inner half of the volume Vmax and half in the outerhalf. So, on average, we expect V/Vmax=0.5
The V/Vmax test
In an expanding Universe the luminosity distance must be used in placeof r and rmax and the constant density assumption becomes one ofconstant density per unit comuving volume .
Luminosity function
In most samples of AGN <V/Vmax> > 0.5. This means that the luminosityfunction cannot be computed from a sample of AGN regardless of their z.Rather we need to consider restricted z bins.
More often sources are drawn from flux-limited samples, and the volumesurveyed is a function of the Luminosity L. Therefore, we need to accountfor the fact that more luminous objects can be detected at larger distances and are thus over-represented in flux limited samples. This is done by weighting each source by the reciprocal of the volume over whichit could have been found:
X-ray selected AGN luminosity functionsluminosity dependent density evolution
2-10 keV AGN luminosity function models
LDDE with variable absorbed AGN fraction La Franca et al. 2005
2-10keV
0.5-2keV
Comparison with HC models
The cosmic backgrounds energy densities
Assume that the intrinsicspectrum of the sourcesmaking the CXB has E=1
I0=9.810-8 erg/cm2/s/sr
’=4I0/c
Optical (and soft X-ray) surveys gives values 2-3 times lower than those obtained from the CXB (and of the F.&M. and G. et al. estimates)
Black hole mass density
A ~ 5x1039 erg s-1Mpc-3
A (1-) LBol
BH ~ ——————
c2 LX
=0.1 LBol/LX=40
BH ~ 3x10-5 MΘ Yr-1 Mpc-3
BH ~ 4x105 MΘ Mpc-3
.
.
BH growth
CXB and SMBH census
Two seminal results:1. The discovery of SMBH in the
most local bulges; tight correlation between MBH and bulge properties.
2. The BH mass density obtained integrating the AGN L.-F. and the CXB that obtained from local bulges
most BH mass accreted during luminous AGN phases! Most bulges passed a phase of activity:
Complete SMBH census and full understanding of AGN evolution to understand galaxy evolution
Local SuperMassive Black HoleAGN are powered by accretion on a SuperMassive Black Hole of 106-1010M, Thus SMBH should exist in the nuclei of all galaxies that have experimented a violently active phase.
Are all local SMBH relics of AGN activity?Do other mechanisms, as merging, play a role?
There are strong correlations between the BH mass and host galaxy properties: bulge luminosity and mass and central stellar velocity dispersion.
These correlations can be used to estimate the mass function of local BH and thus their total mass density BH in the local Universe.
Is possible to answer this question comparing the local BH mass function with that of AGN
The mass function of local BH
-(x)dx number of galaxies per unit of comoving volume with observable x between x and x + dx
-logMBH = a + blogx log linear correlation between the BH mass and the observable x
-(MBH) intrinsic dispersion; it is similar for all the correlations is one refers only to galaxies with secure BH detection
Number of BH with mass between MBH and MBH+dMBH, and observable between x and x + dx
Then the local BH mass function is …
and the total mass density of local BH is
if the observable x is the bulge luminosity L
It is important to test that the MBH- and MBH-Lbul correlation derived from a selected sample are consistent.
The selected sample is a SDSS sample of 9000 early type galaxy for which it is possible to determine independently the velocity and luminosity functions.
BHMF from the MBH-s correlation
The MBH- correlation from a group of selected early type of galaxy with secure determination of BH mass is:
log MBH=(8.300.07)+(4.110.33)(log-2.3)
The assumed velocity function is that by Sheth et al. 2003 for early type galaxy.
1000 Montecarlo realization of the BH mass function were computed by randomly varying the input parameters .
These parameters are assumed normally distributed, and their 1 uncertainties are given by their measurement errors.
Two BHMF with (MBH)=0 and (MBH)=0.3.
BHMF from the MBH-Lbul correlation
The MBH-Lbul correlation from the group of selected early type galaxy with secure determination of BH mass in the K band is:
log MBH=(8.210.07)+(1.130.12)(logLK,bul-10.9)
The luminosity function is that by Bernardi et al. 2003.
In the case of S0 galaxy the bulge luminosity has to be corrected for a factor m, and is related to the total luminosity by:
bulge(m)=fS0(m-m)/(fE+fS0) fE~0.1, fS0~0.2
The correction factor m is few dependent on the photometrical band, thus in the computation of the bulge luminosity function is possible to assume the B band.
The use of the MBH- correlation is more secure because it has not to be corrected for the bulge fraction, but it is more difficult to measure
The BHMFs derived from the two correlations
• The effect of a dispersion in the correlation is that to softening the decrease of the BHMF at high mass thus increasing the total density
• The use of the same intrinsic dispersion provide consistently BHMF’s with the same mass densities BH
The BHMF for Early Type GalaxiesCan the use of luminosity functions from different galaxy survey and photometric band affect the determination of BHMF in early
type galaxy?
• Bernardi et al.: SDSS (3500-9000 A) sample of 9000 early type galaxies;
• Marzke et al.: CfA survey (B(0)≤14.5); the luminosity function is for morphological type and the luminosities are in Zwicky magnitudes
• Kochanek et al.: luminosity function in the K band
• Nakamura et al.: SDSS sample; luminosity function in the r* band
The different BHMF are in good agreement. Discrepancies arise only at low mass, MBH<108M0, and are due to the extrapolation of the different functions adopted to fit the data.
The BHMF for all Galaxy types
It has been derived using both the MBH-Lbul and the MBH- correlations. All the BHMF’s and the BH densities BH are in agreement within the errors.
The best estimate in the density of local massive BH is
BH=4.6·105 M0 Mpc-3
About the 70% of this density is given by early type galaxies.
The Mass Function of AGN RelicsI. The continuity Equation
The continuity equation links the relic BHMF N(M, t) to the AGN luminosity function (L, z). AGN are powered by mass accretion on the central massive BH.
is the mean accretion rateon the BH of mass M
During the BH accretion the AGN luminosity is L=LEdd and the mass is converted in energy with efficiency :
The intrinsic AGN luminosity is directly related to the BH accretion.
(L, t) dLog L=(M, t) N(M, t) dM M=BH with mass M active at t
The right term of the eq. containing the source function is equal to zero.All processes, such as merging, that can create or destroy a BH are neglected; the rate is very uncertain and strongly depends on the model adopted.
A fraction of the mass is converted in energy and escape from the BH
with constant and
Integration with initial condition [M, t(zs)]=1, i.e. all the BH are active at the starting redshift zs.
Integration on the mass M gives the density of AGN relics:
with
II. The Bolometric Corrections• AGN luminosity is determined in a limited energy band b; a
suitable bolometric correction, f bol, b=L/Lb is required.
• The observed luminosity is given by the integral of the observed Spectral Energy Distribution. The IR radiation is reprocessed, thus a correction is required.
• A template spectrum is constructed.
Optical-UV band: broken power-law
1=-0.44 1m-1300 A (L~)
2=-1.76 1200-500 A
X-ray band: simple power law + reflection component
=1.9 , Eb=500 keV
• The spectrum, and thus the bolometric corrections, are assumed to be independent on the redshift.
III. The Luminosity Function of AGNAGN surveys are performed in limited spectral bands. The LF found in literature describe only a fraction of the AGN population, i.e. a fraction of the local BHMF.• Boyle et al. 2000: B band, all the population of red quasar is missed
• Soft X-ray (0.5-2 keV): all sources with important absorption are missed, NH>1022 cm-2
• Hard X-ray (2-10 keV): the most of AGNs; object with NH>1024 cm-2 are missed
The first two LFs function are in good agreement at high luminosity.The third LF samples a larger fraction of AGN population at all luminosities. Differential comoving energy density
• Objects with L>1012L0 provide ~ 50 %of the total energy
• High and low luminosity objects have similar redshift distributions
U=1.5·10-15 erg cm-2
BH=2.2·105 M0 Mpc-3
Integration of the continuity equation with =1, =0.1 and zs=3 give ….
• The hard X-ray LF gives the greaternumber of AGN relics
• The number of relic at z=0 is greater than the number of relic at zs.
• BH growth mainly at z ≤ zs. At higherz BH have too little time to growth.
• The relic BHMF is substantially independent on zs, if zs >2.5.
Solid line z=0, Dotted line z=zs, Dashed line only AGN with L >1012L0
The higher mass BH today growth during the quasar phase (L>1012L0).
If <1, the BH can accrete more mass. The number of relic with high mass increases.
Comparison between local BH’s and AGN relics
No correction for missing AGN population
Relic BHMF corrected using hard X-ray LF and accounting for
Compton Thick AGN’s
EXCELLENT AGREEMENT!• Local BH’s are AGN relics mainly grown during active phases of host
galaxy
• Agreement obtained with ε = 0.1 and λ = 1
• Merging processes not important (at least for z < 3)
Constraints from the X-ray Background
It is possible to estimate the expected mass density of relic BH’s from XRB
where
The average redshift of X-ray sources emitting the XRB is…
Perfectly consistent with the local estimate for = 0.1 (consistency requires 0.07< < 0.27)
Accretion efficiency and Eddington ratio
Consider the average square deviation between the logarithms of local and relic BHMF’s
Acceptance region (k2 ≤ 1)
= 0.054, non-rotating Schwarzschild BH
= 0.42, maximallyrotating Kerr BH
Best values (k2 = k2
min): = 0.08, = 0.5
BH’s should be slowly rotating
k2 ≤ 0.72 which corresponds to the “canonical” case (ε = 0.1, λ = 1)
0.1 < λ < 1.7
BH’s grow during luminous accretion phases close to the Eddington limit
Growth and accretion history of massive BH’s
Redshift dependence of ρBH
BH’s accretion proportional to star formation rate + feedback from AGN’s explain the observed correlations MBH - and MBH - Lbul with host galaxies
Cosmic BH’s accretion rate
High mass BH’s grow earlier than low mass BH’s
The lifetime of active BH’s
The active time is
~ 1.5·108 yr MBH > 109 Mo
~ 4.5·108 yr MBH < 108 Mo
~ 109 yr smaller and
AGN’s which leave smaller relic masses need longer active phases
Results in agreement with upper limit of 109 yr set by variability timescale
Summary
• Local BH’s are AGN relics mainly grown during active phases of host galaxy, in which accreting matter was converted into radiation with efficiencies ε = 0.04 – 0.16 at a fraction λ = 0.1 – 1.7 of the Eddington luminosity
• Merging processes are not important at redshift z < 3
• BH’s growth is anti-hierarchical
• The average total lifetime of AGN’s active phases ranges between 108 and 109 yr depending on the BH mass