Dynamical Phenomena for Bulge and Disk Formation Françoise Combes Ringberg, 21 May 2010 Outline:  Disk formation scenarios  AM transfers, radial migrations  Bars and gas flows  Bulge formation scenarios

2 Disk formation 1- Fall & Efstathiou (1980), van der Kruit (1987) AM conservation during the collapse of a uniformly rotating uniform sphere (r m =0.2h)  produces an exponential disk, with a cut-off at 4.5h HI extensions accreted later?? Van der Kruit 1987 The baryons cannot lose AM, since it is barely sufficient  Disks too concentrated

3 Possible scenarios 2- Star formation threshold, for the stellar exp disk (Kennicutt 1989) But extended UV disks: 2 SF prescriptions? 3- Maximum AM of the cooled gas (van den Bosch 2001)  But again, large central concentration Z f begin to accrete with a speed ~a M= 5 E11 Mo, =0.129 Problem:AM acquired by tidal torques before virialisation In mergers, baryons lose AM against DM  Too small disks Gas-dominated mergers at high z? (Robertson et al 2006)

4 Surface density breaks Debattista et al 2006 Face-on Edge-on Consequence of AM exchange Outer and inner disks breaks Rbreak ~ ROLR Could be a stellar processus (Pfenniger & Friedli 1991) Or a gas process, with SF threshold (Roskar et al 2008)

5 Break moves radially outwards Roskar et al 2008 TreeSPH simulation of collapse: break moves due to gas break and Toomre Q increase Stars Gas SFR Age  Spiral and bar transfer inner stars to the outer parts

6 Age gradient reverses after 8kpc M33: CMD diagrams from HST/ACS (Williams et al 2009) --- Mo et al 1998, … all radii _____ inside 8kpc

7 Migrations of stars and gas Resonant scattering at resonances Sellwood & Binney 2002 All stars with small epicycles LL CR ILR OLR

8  L exchange without heating Sellwood & Binney 2002 Invariant: the Jacobian E J = E-  p L   E =  p  L  J R = (  p -  )/   L If steady spiral, exchange at resonance only In fact, spiral waves are transient The orbits which are almost circular will be preferentially scattered

9 Chemical evolution with migration Shoenrich & Binney 2009 O/H, and O/Fe Thick disk is both  -enriched and low Z Churning = Change in L, without heating Blurring= Increase of epicyclic amplitude, through heating Gas contributes to churning, and is also radially driven inwards

10 Transfert of L, and migrations Bars and spirals can tranfer L at Corotation Transfer multiplied if several patterns with resonances in common Much accelerated migrations Minchev & Famaey 2010 Bar Spiral

11 Effect of coupled patterns Time evolution of the L transfer with bar and 4-arm spiral, in the MW Top: spiral CR at the Sun Bottom: near 4:1 ILR Minchev et al 2010

12 Migration extent Time evolution of the L transfer with bar and 4-arm spiral Explains absence of AMR Age Metallicity Relation +AVR relation Initial position of stars ending in the green interval after 15 and 30 Rotations Black: almost circular  = 5km/s Minchev et al 2010

13 Bar+spiral migrations Overlap of resonances Minchev et al 2010

14 Bars formation and re-formation Self-regulated cycle:  Formation of a bar in a cold disk  Bar produces gas inflow, and  Gas inflow destroys the bar +gas accretion Gas accretes by intermittence First it is confined outside OLR until the bar weakens, then it can replenish the disk, to make it unstable again to bar formation 2% of gas infall is enough to transform a bar in a lens (Friedli 1994, Berentzen et al 1998, Bournaud & Combes 02, 04) Time (Myr) Bar Strength

15 No gas accretion gSb-dmx no

16 With gas accretion gSb-dmx ac

17 gSb models --- Purely stellar --- With gas and SF+feedback --- With gas accretion (5Mo/yr) --- Double accretion rate (10Mo/yr) Mhalo=Mbar

18 Scenarios of bulge formation In major mergers, the tidal trigger first forms strong bars in the partner galaxies, which drive the gas inward  Formation first of a pseudobulge Then the merger of the two galaxies could provide a classical bulge Which will then co-exist with the pseudo ones Alternatively, after a classical bulge has formed subsequent gas accretion, could re-form a bar, and a disk and drive the gas towards the center,  pseudobulge Clumpy galaxies at high z  bulge formation Again problem for the bulgeless galaxies  Major mergers  Minor mergers  Bars  Clumps

19 Major merger, N4550 prototype  bulge formation gasstarsgasstars

20 2 CR stellar disks, but only one gas rotation starsgas Red= prograde galaxy, Blue= retrograde galaxy, Black=total

21 Angular momentum exchange Crocker et al 2008 Formation of a bulge with low n ~1-2 Special geometry, of aligned or anti-aligned spins Red= prograde galaxy, Blue= retrograde galaxy, Black=total Full lines= orbital AM, Dash lines= individual spins The gas settles in corotation with the thicker, more perturbed, disk

22 Pseudo-bulge formation Pseudobulges have characteristics intermediate between a classical bulge (or Elliptical) and normal disks (Kormendy & Kennicutt 2004)  Sersic index  ~ r 1/n, with n =1-2 (disks: n=1, E: n=4 or larger)  Flattening similar to disks, box/peanut shapes  Bluer colors  Kinematics: more rotation support than classical bulges Combes & Sanders 1981 Combes et al 1990

23 Multiple minor mergers Bournaud, Jog, Combes mergers of 50:1 mass ratio Even more frequent Than 1:1 The issue is not the mass ratio of individual mergers But the total mass accreted If 30-40% of initial mass  Formation of an elliptical

24 Formation in clumpy galaxies Rapid formation of exponential disk and bulge, through dynamical friction Noguchi 1999, Bournaud et al 2007 Chain galaxies, when edge-on Evolution slightly quicker than with spirals/bars?

25 Frequency of bulge-less galaxies Locally, about 2/3 or the bright spirals are bulgeless, or low-bulge Kormendy & Fisher 2008, Weinzirl et al 2008 Some of the rest have both a classical bulge and a pseudo-bulge Plus nuclear clusters (Böker et al 2002) Frequency of edge-on superthin galaxies (Kautsch et al 2006) 1/3 of galaxies are completely bulgeless SDSS sample : 20% of bright spirals are bulgeless until z=0.03 (Barazza et al 2008) Disk-dominated galaxies are more barred than bulge-dominated ones How can this be reconciled with the hierarchical scenario?

26 BRAVA kinematical results: Milky Way The bulge of the Milky Way is compatible with only pseudo Old stars (99% > 5Gyr) +a large variety of O/H, Fe/H Fe/H decreases with z  Not only a bar? (Zoccali et al 2008) Shen et al 2010 BRAVA+ Rangwala et al 2009

27 Age (Gyr) bulge halo Metallicity indicators Bulge stars are old and  -enriched But inner disk stars are not known Zoccali et al 2009 bulge thick thin

28 No possible classical bulge Even a classical bulge of 8% Mdisk worsens the fit to the data Shen et al 2010 Older, low Fe/H stars have been scattered at high z, for a longer time Several bars?

29 NGC 4565: SBb, No classical bulge In addition to the bar, a pseudo-bulge of 6% in mass Pseudo, since flattened, and Sersic index HST 1.6  m Kormendy & Barentine 2010 Spizer-3.6  Spizer-8 

30 Thick disk formation 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)  Orbit excentricity of stars could help to disentangle Sales et al 2009 SB09

31 CONCLUSION  Disk formation poses problems to the standard model: too concentrated, too small, loss of AM  Radial migration, resonant scattering by spirals  Bars efficient to AM exchange, gas radial flows  Fraction of bulgeless galaxies: challenge for hierarchical scenario?  Thick disk formation: several scenarios  Bulge formation: coexistence of many processes Some major mergers could keep a disk Multiple minor mergers lead to spheroids Clumpy galaxies at high-z