The Building Up of the Black Hole Mass- Stellar Mass Relation

1. 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 Roma 2Max-Planck-Institut fur Extraterrestriche Physik

2. 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)

3. The local MBH-M* relation Haring & Rix 2004 The growth of SMBH is slower than the stellar mass assembly The growth of SMBH is faster than the stellar mass assembly Tight link between the growth of SMBH (AGN phase) and the formation of the host galaxy.

4. The MBH-M* relation of high z AGN BL AGN 1<z<2.2 AGN 1<z<4.5 Peng et al. 06 Merloni et al. 09 QSO 3.9<z<6.4 M* from CO data: radio loud AGN 0<z<2 Maiolino et al. 07 Walter et al. 04 McLure et al. 06 Riechers et al. 08, 09 virial MBH: Barth et al. 03 Dietrich & Hamann 04 Shields et al. 07 Riechers et al. 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

5. The MBH-M* relation of SMG Alexander et al. 2008 η=Lbol/LEdd 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

6. 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 Menci et al. 2005, 2006 Properties of DM merging trees 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 Phase 1 Phase 2

7. 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: • quiescient star formation (dm*/dt~mcold/τd) • starburst driven by (major+minor) merging and fly-by events • Supernovae feedback returns part of the cooled gas to the hot gas phase Menci et al. 2005, 2006 Frequent galaxy interactions Rapid cooling (high gas density) Starbursts with large fraction of gas converted into stars Drop of interaction rate Decline of cooling rate Quiescent and declining star formation z>2 z<2

8. 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. Menci et al. 2006,2008 Black hole accretion rate Fraction of accreted gas • Larger fraction of accreted gas for • massive haloes • high z (m’/m≈1) Interaction rate Higher interaction rate at high z Σ => cross section

9. The predicted MBH-M* relations z=0.1 z=4 local relation high-z QSO Haring & Rix 2004 Marconi & Hunt 2003 Evolutionary paths followed by BH with MBH(z=0)>1010 M Lamastra et al. 2009 MNRAS submitted

10. Selecting massive BHs at high z Starformation BH accretion Γ >1 when we select MBH >109 M at z≥4 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 Lamastra et al. 2009

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

12. Selecting gas-rich, star forming galaxies at z=2-3 datapoints: Alexander et al. 2008 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) Lamastra et al. 2009

13. local relation 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=4.4x10-5 Mpc-3 (fgas>0.6) predicted space density: Φ=1.9x10-5 Mpc-3 (fgas>0.7) Lamastra et al. 2009

14. The distribution of Γ for all galaxies Lamastra et al. 2009

15. 5% of the final mass 50% of the final mass 90% of the final mass Mass dependence of Γ(z) Lamastra et al. 2009 Downsizing in the assembly of BH masses Massive local galaxies have formed preferentially through path passing above the local MBH-M* relation Marconi et al. 2004

16. 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=1-2 • Γ≃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