Bars, Spiral Structure, and Secular Evolution in Disk Galaxies

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1 Bars, Spiral Structure, and Secular Evolution in Disk Galaxies Bruce Elmegreen IBM T.J. Watson Research Center Terschelling, 5 July 2005 (+ see review on secular evolution [pseudobulges] in Kormendy & Kennicutt ARAA 2004)

2 Overview Bar evolution today do they dissolve? do they form lenses? Bar formation at intermediate to high z observations and limitations what happens in gas-rich and clumpy disks? Disk and spiral formation at high z clumps, clumps, clumps, Summary of secular evolution effects over a Hubble time

3 Secular Bar Evolution Bars get stronger with time, slow down by disk/halo interactions, change shape to populate more orbital families Weinberg 85; Debattista & Sellwood 98, 00 (see Sellwood s talk) Bar amplitude swing amplification with (top) and without live halo disk ang. mom. halo pattern speed corotation semi-major axis Debattista & Sellwood 00 same disk/halo momentum exchange for spiral waves too (Fuchs 04)

4 Secular Bar Evolution Bars get stronger with time, slow down by disk/halo interactions, change shape to populate more orbital families Weinberg 85; Debattista & Sellwood 98, 00 (see Sellwood s talk) Vertical resonances thicken bars Sanders & Combes 81 Sanders & Combes 81

5 Secular Bar Evolution Bars get stronger with time, slow down by disk/halo interactions, change shape to populate more orbital families Vertical resonances thicken bars Weinberg 85; Debattista & Sellwood 98, 00 (see Sellwood s talk) Sanders & Combes 81 Gas accretes to inner regions, steepens inner rotation curve, causes ILR to appear, causes nuclear rings & nuclear starbursts, may cause secondary bars NGC 2681 Erwin & Sparke 99

6 Secular Bar Evolution Bars get stronger with time, slow down by disk/halo interactions, change shape to populate more orbital families Weinberg 85; Debattista & Sellwood 98, 00 (see Sellwood s talk) Vertical resonances thicken bars Sanders & Combes 81 Gas accretes to inner regions, steepens inner rotation curve, causes ILR to appear, causes nuclear rings & nuclear starbursts, may cause secondary bars Growth of ILR radius with time depopulates bar-supporting orbits (which are between the ILR and the 4:1+ resonances), possibly dissolving the bar into a bulge Hasan & Norman 90, Friedli & Benz 93, Hasan, Pfenniger, Norman 93 e.g., Das et al. 03 found inverse correlation between bar ellipticity and gas concentation fmc = vbulge2 Rbulge / vbar-end2 Rbar-end (Das et al. 03)

7 Norman, Sellwood, & Hasan 96 models of bar dissolution. 50,000 particles stars only, 2D only 0%, 3% and 5% of total mass shrunk to core in 150 time steps Bar amplitude versus time Bar amplitude versus central mass

8 Norman, Sellwood, & Hasan 96, 200,000 star particles, 3D 5% of total mass shrinks to core

9 Shen & Sellwood 04 (3D stars-only, no active halo), find bars are relatively robust, and bar weakening occurs in 2 phases: initially fast (x1 orbit scattering) and then slow (from slow potential changes) strong initial bar weak initial bar Central mass concentration increases to 2% of the disk mass (>> central BH masses), showing no bar destruction. Bar weakens more with compact core than diffuse core of the same mass (2% Mdisk) Compact core (solid line) destroys bar with 4% Mdisk Diffuse core (dashed) needs more, >10% Mdisk

10 Athanassoula,Lambert & Dehnen 05 found bars with massive active halos survived with increasing central mass (up to 10% disk mass), while bars with low-mass active halos were destroyed. Bars speed up as they weaken.

11 What happens to old bars? bar major disk major disk minor disk major disk minor Kormendy 77: Lens: - not spheroid or exponential disk - shallow brightness profile - sharp cutoff (Sandage 1961, Freeman 1975) Kormendy 1979 suggested lenses are dissolved bars. That is, S0 galaxies with lenses formerly had bars. VII Zw 793 / VII Zw 421 / II Zw 67 (cf. Athanassoula 1982)

12 Bar/Lens versus Hubble Type NGC 936 SB02/3/SBa NGC 3992 SBb NGC 4314 SBa NGC 5236 SBc

13 Lenses could be dissolved bars (Kormendy 1979) Of 121 low inclination, bright SB0SBd galaxies: 54% of SB0-SBa have lens, 0% of SBab-SBc do 16% have both bar and lens, and bar size = lens size Inner ring size = lens size for a given MB Bar color = lens color Bars look like they dissolve into a lens (NGC 5101) Axial ratio distribution weakly suggests lenses are thick (triaxial) Presence of lenses in half of early type bars and in a small fraction of early type non-bars suggests early type bars dissolve slowly into lenses. Pure star model by Debattista & Sellwood 00 shows ring formation at bar end.

14 Do bars dissolve into bulges after they form lenses? Recall NGC 5101 has an incipient lens. The 2MASS image shows that the bulge still dominates and is much smaller than the bar. This bar is not turning into this bulge any time soon àno clear examples of bar dissolution into a bulge today àbars may dissolve into lenses, however, and àbars may have dissolved into bulges at very early times

15 Bars in the deep field of the Tadpole Galaxy HST ACS (z~0.8) Bars look normal out to 7 Gy ago, although the spiral galaxies can be a little smaller (E,E, Hirst 04)

16 Small bars could have made bulges quickly at high z UDF spiral scale lengths (kpc) using WMAP LCDM cosmology High z spiral galaxies are small and dense spirals à Toomre length (2oGS/j2)~Rdisk à j large like the inner regions of today s galaxies R ~ 1/H(z)2/3 ~ 1/(1+z) (Mo, Mau & White 98) subsequent accretion filled out halo and disk with lower density DM+gas First bars that formed could have made bulges nuclear black hole (if formed) was a larger mass fraction then bar evolution had a faster dynamical time when the bar was smaller (i.e., the density was high) bar evolution would have been strongly influenced by abundant dense gas (Bournaud & Combes 2002) van der Kruit 87: scale lengths for local galaxies Today s big bars could form later in today s disks and dissolve slowly or not at all

17 Bar evolution at high z is difficult to observe directly Bars in the Tadpole Galaxy deep field. Bar Fraction vs size Bar Fraction vs inclination (EE04)

18 Nevertheless, bar fractions appear about constant to z~1 (Tadpole field) (EE04) Local: RC3 bar fractions GOODS field: f ~deep Tadpole fieldfor face-on spirals out to z~1 (Jogee et al. 04) If bars formed early in unstable disks, and if they turned into bulges over a Hubble UDF: f ~ 26/269 ~ 0.1 for all spirals time, then you might expect a higher bar (E,E, Rubin & Schaffer 05) fraction in the past. Barà bulge conversion has to be even earlier also Zheng et al. 05

19 Extremely Young Bars: Observational Limitations WMAP cosmology: WL=0.73, WM=0.23, H=71 Beyond z~1, galaxies are only a few Gy old, not relaxed Between z~0.6 and 4.6, 2 kpc objects are smaller than 10 px on ACS camera Beyond z~4, Freeman disks are not easily seen Beyond z~3, redshift range corresponding to a bar formation time of 0.5 Gy gets large, Dz~1

20 clumpy bars in exponential disks bars in clump-clusters (Elmegreen, Elmegreen & Hirst 2004)

21 At high z, most galaxies are very clumpy UDF Spirals UDF Ellipticals (30/100 had clumps) Chains à Clump clusters UDF Chains

22 Galaxy classification in the UDF (Debbie s poster) Chain Clump cluster Double Tadpole Spiral Elliptical Clumpy spirals: Abraham et al. 96; Conselice 04; Chains: Cowie et al. 95, van den Bergh et al. 96; Diffuse Objects: Reshetnikov, Dettmar & Combes 03; Conselice et al. 04; Protospirals: van den Bergh 96; Tadpoles: van den Bergh et al. 96; Doubles: van den Bergh 2002

23 Star Formation Clumps: What they tell us Photometric z from clumps (<z>~2.3) Bruzual & Charlot 03, Rowan-Robinson dust (and x2, x4) Madau 95 intergalactic H absorption Clump masses, ages, densities Interclump ages and densities Average clump: Mass ~ 6x108 MO, Diameter ~ 1.8 kpc, age ~ 300 My SF decay time ~ 100 My, Total clump mass fraction ~0.2 Average galaxy: Mgal ~ 6x1010 MO, Dgal ~ 20 kpc, Vrot ~ 150 km s-1 (EE05)

24 Clump Formation High clump masses imply large clump velocity dispersions Dv ~ 24 km s-1 on average Need fast ISM turbulence if formation by gravitational instability Consistent with thick disks Pre-collapse turbulent energy likely from accretion (Dv ~vrot/5) modeled by Noguchi 96, Immeli et al. 04 Clumps could have been accreted as intergalactic gas+star blobs (EE05)

25 Clump Dispersal Clump internal dynamical time tdyn ~ 40 My ~ 0.1 clump age à bound super clusters (dwarf galaxies?) <SFR> ~ 20 MO/yr, current SFR ~ 2 MO/yr tdyn*vrot/dgal ~ 0.3 à tidal forces important Clumps should be dispersing by tidal disruption in ~few orbits Clump sizes à will blend to form thick disk Clump collisions à merge to bulge? (Noguchi 99, Immeli et al. 04) (EE05)

26 SUM: Evolutionary effects over a Hubble Time Non-secular: Interactions, major mergers, cluster motion Strong interactions form bars (Noguchi 88, Gerin et al. 90, Sundin et al. 91, Berentzen et al. 04) Binary companions make bars and earlier Hubble type (EE90) Bars more common in perturbed galaxies (Varela et al. 04) Major mergers form ellipticals (Toomre & Toomre 72, Schweizer 1998, Barnes & Hernquist 92 +) + globular clusters (Ashman & Zepf 92) + counterrotating cores (Kannappan & Fabricant 01) Minor mergers thicken disks (Walker et al. 96; Schwarzkopf & Dettmar 00; Bertschik & Burkert 02; Gilmore et al. 02) Interactions form dwarfs in tidal tails (Zwicky 1956, Barnes & Hernquist 92, Elmegreen et al. 93, Duc et al. 04) Cluster ram pressure strips gas (Gunn & Gott 72, Warmels 86, Hoffman et al. 88; Cayatte 90, ) Formation of ring galaxies, polar ring galaxies, warps, tidal tails,...

27 Secular: Interactions, accretion Hierarchical build-up, continuous accretion of dwarfs, galaxy harassment, accretion of gas, globular cluster accretion from dwarfs, halo streams, Secular: internal Bar/spiral torques drive inner accretion and outer spreading Gas accretion at resonances make star-formation & rings Scattering and vertical resonances thicken disks Bars dissolve into lenses and (maybe) bulges Gas converts to stars Gas viscosity redistributes disk gas

28 Kormendy & Kennicutt 2004

29 General trends over a Hubble time Late à early types Central concentration, less gas, less star formation, hotter disks, redder populations, more metals, Increasing mass and size over time for z>1 and for latetype spirals (accretion, coalescence) Decreasing mass and size of galaxies that form stars ( downsizing ) most massive galaxies completed star formation first More and more isolation (flocculent spirals appear late) THE END Happy 4th!