1. The Building Up of the Black Hole Mass- Stellar Mass Relation Alessandra Lamastra collaborators: Nicola Menci 1, Roberto Maiolino 1, Fabrizio Fiore 1, Andrea Merloni 2 1 INAF - Osservatorio Astronomico di Roma 2 Max-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 M BH -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

4. The M BH -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 M BH : Barth et al. 03 Dietrich & Hamann 04 Shields et al. 07 Riechers et al. 09

5. The M BH -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=L bol /L Edd

6. Initial (z≈4-6) merging events involve small clumps with comparable size High merging rate Last major merging at z≈3 for M≈3X10 12 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

7. 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 Baryonic processes The gas at virial equilibrium with DM haloes undergoes radiative cooling. The cooled gas mass (m cold ) settles into a rotationally supported disc, with radius r d, rotation velocity v d, and dynamical time τ d =r d /v d Two channels of star formation may convert the cold gas into stars: 1.quiescient star formation (dm * /dt~m cold /τ d ) 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

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. 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 Σ => cross section Higher interaction rate at high z

9. z=0.1 The predicted M BH -M * relations Haring & Rix 2004 Marconi & Hunt 2003 Lamastra et al. 2009 MNRAS submitted Evolutionary paths followed by BH with M BH (z=0)>10 10 M  z=4 local relation high-z QSO

10. Selecting massive BHs at high z Γ >1 when we select M BH >10 9 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

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

12. 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

13. Selecting gas-rich, star forming galaxies at z=2-3 The low redshift descendants of SMGs are predicted to have BH with M BH =10 8 - 10 9 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 relation

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

15. Mass dependence of Γ(z) Massive local galaxies have formed preferentially through path passing above the local M BH -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

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 (L bol ≥10 44.5 erg/s) QSO at z=1-2 Γ ≃ 4 for massive (M BH ≥10 9 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 (L X ≥10 43 erg/s, large SFR and gas fraction ). These evolve to local galaxies with masses M BH < 10 9 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