Secular Evolution of Disk Galaxies Bruce G. Elmegreen IBM T.J. Watson Research Center Yorktown Heights, NY “Dynamics of Disk Galaxies,” Seoul National University, South Korea October 21-24, 2013
Star Formation History of the Universe Blue = direct from uv light Yellow = dust corrected Bouwens +11 Reionization requires a SFR ~ 0.018([1+z]/8) 3 (Shull +12) which is consistent with reionization by z~7
Depletion fgas Time Saintonge +13: Depletion time decreases as 1/(1+z) and gas becomes more molecule-rich with z
On cosmological scales with short depletion times, accretion determines the star formation rate For a galaxy: d Mgas d Mgas - SFR = dt dt accretion n where SFR = A Mgas Mgas d Mgas is SFR ~ solution for time >> SFR dt accretion Dave, et al. (2012): “equilibrium SF”
Star Formation History of the Universe High accretion rates Blue = direct from uv light Yellow = dust corrected Bouwens +11
Disk 160 kpc x160 kpc Chaotic galaxy formation in a simulation with cold and hot flows: wild instabilities and big clumps σ /V rot high because of inflow energy & high Σ gas (Q Toomre ~1) clump size/galaxy size ~ ( σ /V rot ) 2 Ceverino, Dekel & Bournaud 2010
Newman +12: Kinematic properties of clumps in a z~2 galaxy Blue-shifted line wings suggest massive winds σ ~ 85-290 km/s Vwind~400-800 km/s . M/SFR ~ 1-8 see also Genzel +11 for other clump winds; Steidel +10; Pettini +00; Weiner +09 for general galactic outflows
Bournaud +13: Do clumps survive? -realistic feedback - radiation press. - HII regions - supernovae � Clumps always accrete new gas even as they expel gas in a wind and lose stars by tidal forces
Clump 2C: continuous clump merging & accretion along filaments Bournaud +13
Clump accretion burst � SF burst & Wind burst + stellar loss Bournaud +13
old clumps have formed stars continuously and also lost some stars that they formed youngest clumps contain old field stars that fell in during the clump-forming instability Bournaud +13
Persistence of clump torques • Observed ~200 Myr stellar age (EE05-09, Wuyts +12) – may correspond to ~400 Myr real age • Clump mass dominated by gas (5xM stars – Bournaud +13) – 10 8 – 10 9 M O produce strong torques • The high fraction of clumpy galaxies (40% at z~2 in E05 & Wuyts +12) implies that clump formation is a long-lived phase (even if individual clumps last 200-400 Myr) � High clump torques persist for 1 Gyr or more at z>1 • Cacciato +12 models make clumpy disks until z~0.5 because of continued gas accretion (e.g., Dekel +09, �) – many epochs of clump formation/migration/destruction – disks stabilize when stars dominate gas (clumps � spirals)
Star Formation History of the Universe clumpy phase Blue = direct from uv light Yellow = dust corrected Bouwens +11
Fathi +12: Disks are exponential even at z=5.3, when the universe is only ~1 Gyr old. Exponential disks need to form quickly. Before spiral arm and bars (which appear a z~1-2) Young disks are also small: 15% today’s size at z=2-5.8
Clump interactions can make exponential disk + bulge Bournaud, Elmegreen & Elmegreen 07
Clumpy disks should also be thick disks • In Milky Way, the similarity in α /Fe (Melendez +08), K-giant abundances (Bensby +10) and ages for bulge and thick disk � bulge and thick disk formed at the same time. • High σ gas at z~2 (Forster-Schreiber +06, Weiner +06, ...) makes clumps big and disk thick for the same reason, the characteristic length of a gravitating object is large (~2 kpc) • L ~ σ 2 / π G Σ
Milky Way thick disk (defined kinematically) has metallicities up to solar. The most metal rich are ~8-9 Gyr old. The thick disk formed from ~12 to ~9 Gyr z=1.3 to... z=3.6 Universe Age 9 Gyr ago The Milky Way’s thick phase lasted until ~9 Gyr ago 12 Gyr ago Bensby +07 Redshift
Minchev et al. 2013 Disk model with accretion and minor mergers. Stellar dispersion increases with age in the solar vicinity. The rapid rise at 8-12 Gyr is from chaotic structures in the young disk
Star Formation History of the Universe Thin disk phase Thick disk & clumpy phase Blue = direct from uv light Yellow = dust corrected Bouwens +11 Question: Is all the z~2 SF going to the thick disk?
Star mass only Thick / Thin disk mass ratios versus circular velocity Assumes conservative ratio of [ M/L ] Thick / [ M/L ] thin ~ 1.2 (gives the least thick disk mass) Star + gas mass Thick disks contain about 1/3 of the total disk mass Comeron, Elmegreen, et al. 2012 (based on Spitzer 3.6 mm survey of vertical disk light profiles)
The thick disk stellar mass is 1-4 x 10 10 M O for V c = 200 km/s. Thick disk star mass That is from a high SF rate of 10-20 M O /yr for ~ 1-2 Gyr (the duration of the clumpy phase) Thin disk star mass The thin disk stellar mass is 4-8 x 10 10 M O for V c = 200 km/s. That is from a low SF rate of 4-8 M O /yr for ~ 10 Gyr (the duration of the spiral phase) V circular Answer: YES, all SF before z~2 can be in the thick disks today and all SF after z~2 can be in the thin disks
Bars are not formed by, nor drivers of, secular evolution at z>1 Suggests: thick/clumpy phase does not make bars. Sheth + 2010
When do spirals appear? varying percentage of disk:bulge:halo 80:0:20 Gas Stars The clumpy phase is disk-dominated (>80% stars + gas in disk). Thick disks, bulges and stellar halos (from the clumpy/merger phase), precede the main spiral phase. Bournaud & Elmegreen 09
Law +12: z=2.18 spiral galaxy: the oldest spiral found - probably tidal, thick arms (high velocity dispersion)
Elmegreen +13: Looking for thick or irregular arms in the HST UDF z=1.03 z=1.24 z=0.92 Grand Design Multiple Thin Arm z=0.60 z=0.29 z=0.53 “Woolly” z=0.50 z=0.78 z=1.11 Intermediate? “Irregular Long Arm” z=0.25 z=0.03 z=0.50 Flocculent color = ACS B, V, I B/W = WFC3 H band z=0.12 z=0.63 z=1.37
More examples of the intermediate types: H-band “Woolly” z=1.32 z=1.41 z=0.78 z=0.95 z=0.51 z=0.69 “Irregular Long Arm” z=0.47 z=1.40 z=2.58 (Not a resolution difference: new types span a wide range of redshift, and beyond z~1, spatial resolution is about constant anyway.)
• Earliest spiral in the UDF: z~1.8 • Earliest Multiple Thin-Arm at z~0.6 • Multiple Thin-Arm and Woolly galaxies are largest and brightest • Flocculents are the faintest
Star Formation History of the Universe Thin disk & bar/spiral phase Thick disk & clumpy phase Blue = direct from uv light Yellow = dust corrected Bouwens +11
SUM: Cosmological Secular Processes • clump stirring z > 2 � thick exponential disk, bulge, spheroid • bars and spirals appear z~1-2 – thin disk phenomena – need stabilizing bulge/thick disk/spheroid • simultaneous with non-secular processes: – mergers, minor mergers, gas accretion
Modern Secular Processes • Angular momentum transfer inside disk and between disk and halo – formation of “pseudobulges” (radial accretion) – bar growth and slowing down • Stellar scattering * • disk growth • formation of “outer disk,” • formation of exponential profiles • Bar thickening, vertical resonance • plus continued accretion and mergers
Modern Secular Processes • Angular momentum transfer inside disk and between disk and halo – formation of “pseudobulges” (radial accretion) – bar growth and slowing down • Stellar scattering * • disk growth • formation of “outer disk,” • formation of exponential profiles • Bar thickening, vertical resonance • plus continued accretion and mergers
Hohl 1971 initially uniform disk forms bar forms exponential profile
Sellwood & Binney 2002: spiral growing from groove instability scatters stars around corotation: Stars initially outside CR lose angular momentum and stars inside CR gain angular momentum.
1. pattern speeds 2. stellar L changes A stellar disk forms many transient spirals that scatter stars R-final around their histograms CRs all over 3. CR features highlighted the disk. Sellwood & Binney 2002
Minchev et al. 2012: multiple spirals stimulated at resonances, all with different pattern speeds. Stellar angular momentum scatters at CRs, but mostly with the bar. Scattering elsewhere is not CR scattering, but scattering in the time-changing potential of multiple spirals. -- see also Roskar et al.
Late Hubble Type, Sb Early Hubble Type, S0 Intermediate, Sa Late type has less disk Outer disk moving Bar CR moving extension because the out with time out with time extra gas causes more Bar OLR moving central accretion and a weaker out with time bar, which then scatters less to the main disk, which is therefore less unstable to form spirals. Scattering: extends disk, turns an exponential with a sharp edge into double-exponential Minchev +12
Barker + 2012: An extended outer disk in spiral galaxy NGC 2403 old young SF to 8 scale old stars lengths (image 24 kpc on a side)
young stars Grossi +11: M33 far outer disk, out to here stars extend further than gas, but SF (200 Myr old) still at 60’ Stars where Σ gas ~ 1 M O /pc 2 SF out to ~10 inner disk scale lengths young stars Gas still here SF to here
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