1. Gas Accretion and Secular Processes 1  How much mass assembled in mergers?  How much through gas accretion and secular evolution? Keres et al 2005, Dekel & Birnboim 2006, Ceverino et al 2010 1- Star formation efficiency, history 2- Size of disks and evolution 3- Metallicity gradients 4- Bulges: how to avoid formation 5- Thick disks Françoise Combes 14 December 2011

2. Merger Fraction from GEMS 2 Jogee et al 2009 < 10% of SF in z=0.6 massive galaxies is triggered by major interactions (Robaina et al 2009) Starburst mode at z=2 Only 10% of the SF Rodighiero et al 2011 Herschel-GOODS

3. Merger fraction in the EGS 3 The decrease in SFR in this z-range comes from gas fraction or SF efficiency, but not from the decrease of mergers Lotz et al 2008

4. 4 Relative role of gas accretion and mergers Analysis of results from a cosmological simulation with hydro: most of the SF is due to smooth flows Dekel et al (2009) Fraction of mass acquired from accretion 77% (mergers 23%) until z=0 (Lhuillier et al 2011)

5. 5 AEGIS galaxies Tacconi et al 2010, Daddi et al 2010 Molecular gas at IRAM, at z~2.3 and at z~1.2 High detection rate >75%, in these « normal » massive Star Forming Galaxies (SFG) Quiescent SF, in the main sequence Gas content ~34% and 44% in average at z=1.2 and 2.3 resp. SFR proportional to M * 0.8 (1+z) 2.7

6. Mergers and SSFR 6 Genzel et al 2010

7. 7 Dutton, van den Bosch, Dekel 2010 Accretion rate for a given M in (1+z) 2.25 SSFR history 3 5 9 Stop sSFR at high z: metallicity? Krumholz & Dekel 2011 Mergers dominate at high z? Khochfar & Silk 2011

8. Disk size evolution 8 Bars and spirals re-distribute angular-momentum Log R Log  Stars Gas SFR Age Roskar et al 2008

9. Bar+spiral: radial migrations 9 Overlap of resonances Minchev et al 2010

10. Size evolution with redshift 10 102 SF galaxies at z=1.5-3, about half the radius of local galaxies Nagy et al 2011, z=2-3 Weinzirl et al 2011 re ~(1+z) -   =1.4 Nagy et al 2011  =1.3 van Dokkum et al 2010  =1.1 Mosleh et al 2011 Stellar radii at a given mass are ~half lower, at z=2-3

11. Minor mergers to increase galaxy radius? 11 Newman et al 2011 Candels: search for companions around quiescent red galaxies ~15% Possible if  e < 1Gyr (  e merging time) But possible only for z=1, At z=2 other processes are required

12. Fundamental metallicity relation 12 Requires slow gas infall, chemical time-scale long wrt dynamical Mannuci et al 2010

13. Gas dilution due to flyby: triggered bar 13 Bar drives low-Z gas to the center, and triggers SF Montuori et al 2010

14. Relation between SFR and Z 14 Montuori et al 2010 F= merger

15. Low Bulge Mass in spiral galaxies 15 Weinzirl et al 2009

16. Constraints of bulge formation 16 Major mergers or a large number of minor mergers form a massive spheroid  classical bulge Secular evolution: bars and vertical resonance elevate stars in the center into a pseudo-bulge: intermediate between a spheroid and a disk Frequent for late-type galaxies Clumpy galaxies at high z can also form a bulge, through dynamical friction Solution : most clumps should be disrupted before reaching the center?

17. Thick disk formation 17 At least 4 scenarios: 1) Accretion and disruption of satellites (like in the stellar halo) 2) Disk heating due to minor merger 3) Radial migration, via resonant scattering 4) In-situ formation from thick gas disk (mergers, or clumpy galaxies) Loebman et al 2011

18. 18 Mastropietro et al 2011 Gas accretion May mimick mergers Gas accretion may explain -- asymmetries, lopsidedness -- clumpiness -- maintained SFR

19. CONCLUSION 19  Importance of mergers: only 10% in the second half of the universe <10% of SF is due to mergers  Size of disks: non-axisymmetries redistribute matter Exponential disks + radial migration  Metallicity dilution due to gas accretion, and mergers  Bulge formation: too massive with mergers Pseudo-bulge with bars, secular evolution Clumpy galaxies: how to avoid a too massive bulge?  Thick disk formation: mergers, or secular evolution?

20. Transient Ring formation 20 Mastropietro et al 2011 The ring may disappear If the accretion continues Hoag object (HST)