The Building Up of the Black Hole Mass- Stellar

Mass Relation

Alessandra Lamastra

collaborators:

Nicola Menci1, Roberto Maiolino1, Fabrizio Fiore1, Andrea Merloni2

1 INAF - Osservatorio Astronomico di Roma2 Max-Planck-Institut fur Extraterrestriche Physik

outline

• Predictions for the relative growth of supermassive Black Holes and the stellar mass of host galaxies in the framework of interaction-driven fueling of AGNs within Cosmological galaxy formation.

• Comparison with different observational samples for which estimates of black hole masses and stellar masses are available (high-z QSO, intermediate-z BL AGN, SMGs)

The local MBH-M* relation

Haring & Rix 2004

Tight link between the growth of SMBH (AGN phase) and the formation of the host galaxy.

The growth of SMBH is faster than the stellar mass assembly

The growth of SMBH is slower than the stellar mass assembly

The MBH-M* relation of high z AGN

Peng et al. 06

Merloni et al. 09

McLure et al. 06

Maiolino et al. 07

Walter et al. 04 Riechers et al. 08, 09

The growth of SMBH is faster than the stellar mass assembly

These studies all focus on luminous AGN => biased towars selecting the most massive SMBH

BL AGN 1<z<2.2 AGN 1<z<4.5

radio loud AGN 0<z<2 QSO 3.9<z<6.4

M* from CO data:

virial MBH: Barth et al. 03

Dietrich & Hamann 04Shields et al. 07Riechers et al. 09

The MBH-M* relation of SMG

Alexander et al. 2008

The growth of SMBH is slower than the stellar mass assembly

This study select ultra-luminous, gas rich galaxies => biased towards selecting massive stellar host

η=Lbol/LEdd

Initial (z≈4-6) merging events involve small clumps with comparable size

High merging rate

Last major merging at z≈3 for M≈3X1012 M

At later times, merging rate declines

Accretion of smaller clumps onto the main progenitor

Semi-analytic model of galaxy and SMBH evolution• Galaxy formation and evolution are driven by the collapse and growth of dark matter (DM) haloes, which originate by gravitational instability of overdense regions in the primordial DM density field• The primordial DM density field is taken to be a random, Gaussian density field with Cold Dark Matter (CDM) power spectrum within the “concordance cosmology” (Spergel et al. 2007).•The merging rates of DM haloes are provided by the Extended Press & Schechter formalism (Bondi et al. 1991, Lacey & Cole 1993)

• Monte Carlo realizations of DM merging trees

Properties of DM merging trees

Phase 1

Phase 2

Menci et al. 2005, 2006

Frequent galaxy interactionsRapid cooling (high gas density)Starbursts with large fraction of gas converted into stars

Drop of interaction rateDecline of cooling rateQuiescent and declining star formation

Baryonic processes•The gas at virial equilibrium with DM haloes undergoes radiative cooling. The cooled gas mass (mcold) settles into a rotationally supported disc, with radius rd, rotation velocity vd, and dynamical time τd=rd/vd

• Two channels of star formation may convert the cold gas into stars:

1. quiescient star formation (dm*/dt~mcold/τd)2. starburst driven by (major+minor) merging and fly-by events

• Supernovae feedback returns part of the cooled gas to the hot gas phase

z>2

z<2

Menci et al. 2005, 2006

Accretion onto SMBH and AGN emission•The BH accretion is triggered by galaxy interactions (merging and fly-by events), which destabilize part of the cold gas available by inducing loss of angular momentum.

Black hole accretion rate

Fraction of accreted gas

Interaction rate

Larger fraction of accreted gas for -massive haloes -high z (m’/m≈1)

Menci et al. 2006,2008

ddint /vrτ

Σ => cross section

Higher interaction rate at high z

0)(z0)/M(zM

(z)(z)/MMΓ(z)

*BH

*BH

z=0.1

The predicted MBH-M* relations

Haring & Rix 2004

Marconi & Hunt 2003

Lamastra et al. 2009 MNRAS submitted

Evolutionary paths followed by BH with MBH(z=0)>1010

M

z=4

loca

l rel

atio

n

high-z QSO

Selecting massive BHs at high z

Γ >1 when we select MBH >109 M at z≥4

Lamastra et al. 2009

Star formation

BH accretion

Galaxies formed in biased, high density regions undergo major merging events at high redshifts. At z ≲ 2.5 interaction-driven AGN feeding drops while quiescent star formation still builds up stellar mass bringing Γ→1

0)(z0)/M(zM

(z)(z)/MMΓ(z)

*BH

*BH

Selecting intermediate-mass objects at z=1-2

Galaxies formed in less biased regions of the primordial density field: lower interaction rate at z≳4

The excess Γ>1 is less pronounced

Lamastra et al. 2009

Observations by Merloni et al. 2009: log LX/erg s-1>44.5

0)(z0)/M(zM

(z)(z)/MMΓ(z)

*BH

*BH

Selecting gas-rich, star forming galaxies at z=2-3

Adopted selection critera consistent with those adopted by Alexander et al. 08 Gas Fraction ≥ 0.7 (see Tacconi et al. 06, 08; Swinbank et al. 08) SFR ≥ 100M/yr

Γ(z)<1 for galaxies which retained a large gas fraction at z=2-3 (galaxies originated from merging histories characterized by less prominent high-z BH accretion and starburst)

datapoints: Alexander et al. 2008

Lamastra et al. 2009

0)(z0)/M(zM

(z)(z)/MMΓ(z)

*BH

*BH

Selecting gas-rich, star forming galaxies at z=2-3

The low redshift descendants of SMGs are predicted to have BH with MBH=108-109 M, in agreement with the independent finding of Alexander et al. 2008 on the basis of space density of SMGs.

observed space density of SMG at z=1.-3.5 : Φ=2.5x10-5 Mpc-3 (Swinbank et al. 2006)

predicted space density: Φ=1.9x10-5 Mpc-3 (fgas>0.7)

predicted space density: Φ=4.4x10-5 Mpc-3 (fgas>0.6)

Lamastra et al. 2009

local r

elation

The distribution of Γ for all galaxies

Lamastra et al. 20090)(z0)/M(zM

(z)(z)/MMΓ(z)

*BH

*BH

Mass dependence of Γ(z)

Massive local galaxies have formed preferentially through path passing above the local MBH-M* relation

Lamastra et al. 2009

5% of the final mass

50% of the final mass

90% of the final mass

Marconi et al. 2004

Downsizing in the assembly of BH masses

Conclusions

Interaction-driven fueling of AGNs within Cosmological galaxy formation models yields:

Γ(z)>1 for massive galaxies at high redshift (i.e., when merging histories characteristic of biased, high-density regions of the primordial density field are selected)Γ≃2 for luminous (Lbol≥1044.5 erg/s) QSO at z=1-2Γ≃4 for massive (MBH≥109 M) in QSOs at z≳4

Γ(z)<1 for galaxies which retained a large gas fraction at z=2-3 (i.e., which did not convert the whole gas content into stars at high redshifts)Γ≃(0.3-1) for SMG-like galaxies hosting active AGNs (LX≥1043 erg/s, large SFR and gas fraction ). These evolve to local galaxies with masses MBH < 109 M

At any given z, Γ(z) is predicted to increase with BH mass Corresponds to a ‘’downsizing’’ in the assembly of BH masses

Measuring Γ(z) for an unbiased sample of AGN can provide crucial constraints on interaction-driven fueling scenarios for the growth of SMBHs in a cosmological context