Dynamical Phenomena for Bulge and Disk Formation Franoise 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 LL 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 (Bker 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