1 / 31

Dynamical Phenomena for Bulge and Disk Formation

Dynamical Phenomena for Bulge and Disk Formation. Outline:  Disk formation scenarios AM transfers, radial migrations Bars and gas flows Bulge formation scenarios. Françoise Combes Ringberg, 21 May 2010. Disk formation. 1- Fall & Efstathiou (1980), van der Kruit (1987)

kirsi
Download Presentation

Dynamical Phenomena for Bulge and Disk Formation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

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

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

  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 • 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) Zf begin to accrete with a speed ~a M= 5 E11 Mo, l =0.129

  4. Face-on Edge-on Debattista et al 2006 Surface density breaks 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 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 Roskar et al 2008

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

  8. DL exchange without heating Invariant: the Jacobian EJ= E- Wp L  DE = WpDL DJR = (Wp-W)/kDL If steady spiral, exchange at resonance only In fact, spiral waves are transient The orbits which are almost circular will be preferentially scattered Sellwood & Binney 2002

  9. Chemical evolution with migration O/H, and O/Fe Thick disk is both a-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 Shoenrich & Binney 2009

  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 Bar Spiral Minchev & Famaey 2010

  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 s = 5km/s Minchev et al 2010

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

  14. Bar Strength Time (Myr) Bars formation andre-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)

  15. gSb-dmx no No gas accretion

  16. gSb-dmx ac With gas accretion

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

  18. Scenarios of bulge formation uMajor mergers vMinor mergers wBars xClumps • 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

  19. Major merger, N4550 prototype  bulge formation gas stars gas stars

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

  21. Angular momentum exchange 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 Formation of a bulge with low n ~1-2 Special geometry, of aligned or anti-aligned spins Crocker et al 2008

  22. Pseudo-bulge formation Combes & Sanders 1981 Combes et al 1990 Pseudobulges have characteristics intermediate between a classical bulge (or Elliptical) and normal disks (Kormendy & Kennicutt 2004) Sersic index m ~ r1/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

  23. Multiple minor mergers 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 50 mergers of 50:1 mass ratio Even more frequent Than 1:1 Bournaud, Jog, Combes 2007

  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) BRAVA+ Rangwala et al 2009 Shen et al 2010

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

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

  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 1.3-1.5 HST 1.6mm Spizer-3.6m Spizer-8m Kormendy & Barentine 2010

  30. SB09 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

  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

More Related