III. The Growth of Galaxy Disks and the Evolution of Galaxy Sizes

1. III. The Growth of Galaxy Disks and the Evolution of Galaxy Sizes • Observed galaxies occupy a small fraction of possible structural configurations: size, surface brightness, shapes, etc.. • Stability? • Initial Conditions? • Feed-back during the formation? • Present-day structural properties • Observed Evolution of Galaxy Structure • Comparison to theoretical Expectations

2. Present-Day Parameter Relations ISpheroids/Ellipticals: the “Fundamental Plane” • Djorgovski and Davis 1987 • Dressler et al 1987 • Joergensen et al 1996 • Any two parameters of re,Ie,s predict the 3rd well Explanation elements: • virial theorem • quite uniform (M/L)* • stars dominate at center (?) Joergensen et al 1996

3. Disks Spheroids Disks Spheroids Shen et al 2003 SDSS Present Structural Parameter Relations for Disk GalaxiesI: Disk Size vs Mass/Luminosity • Galaxy size scales with luminosity/stellar mass • At given luminosity/size: fairly broad (log normal) distribution • Rd~M*1/3

4. What determines sizes of stellar disks? Angular momentum Arising from halo size and spin parameter l Dark halo and its adiabatic contraction do matter Peebles ‘69,Fall+Efstathiou ‘80 Conversion of gas to stars Toomre’64,Kennicutt ‘98 Internal re-distribution of angular momentum Bar instabilities? Ostriker&Peebles ’73, Norman et al ‘96 Direct disk formation simulations have been largely unsuccessful “sub-clump” problem Katz ‘91,Navarro&Steinmetz ‘90s,etc.. Semi-analytic approaches to disk formation Dalcanton et al ‘97,Mo, Mao & White 98, van den Bosch ‘99, Naab&Ostriker ‘05

5. Pizagno, Weinberg, Rix, et al 2005 Structural Relations for Disks IIthe “Tully-Fisher” (1976) relation • Tight LB/V vs vcirc relation historically exploited for distance estimates • Tully-Fisher observations to constrain disk formation • Pizagno et al 2005 • Complement SDSS info with Ha rotation curves for 250 galaxies • Sample selection: B/Dmass < 0.2; all colors

6. 2-param. relation 3-param. relation “Maximal” disk “Tully-Fisher” and the structure of disks • Only need L (or M*) to predict Vcirc(2.2Rd) in disk systems • Size does not help to predict Vcirc • Stellar disks in most galaxies “sub-maximal” v*~0.6vtot (@2.2Rd)

7. Let’s use look-back observations to tackle disk formation

8. Disk evolution with redshift: What might we expect? • Sizes from Initial Angular Momentum (Fall and Efstathiou, 1980) • Growth of Halos – Growth of Galaxies (Mo, Mao and White, 1998) Rexp(M*) ~M*1/3x l md-4/3jdx H(z)-2/3 • When did the presently existing disks form? • 1/3 of all stars at z~0 are in disks • 40% of all stars (now) have formed since z~1 (mostly in disks) • Majority of the Milky Way disk stars have formed in the last 7Gyrs  z~1  z~0 is the most important epoch for building today’s stellar disks • Note: higher SFRs at z>0  higher surface brightness(?)

9. Rd~H-1(z) Rd~H-2/3(z) Rd=const (phys.) But first: some loreDisk Evolution from high-z to now If stellar (disk) sizes reflect halo size + constant l zobservation = zformation of halo then Rd~H-1(z) for fixed vcirc(halo) Rd~H-2/3(z) for fixed Mass(halo) Ferguson et al 2004 GOODS But what is observed? • UV-size = f(z) in UV flux-limited sample • Agreement likely fortuitous !?

10. Observing Galaxy Size Evolution • How does the currently observed LV-Rd, M*-Rd, and LV-vc evolve with redshift? • Data Sets • GEMS: 2-band HST imaging + 10.000 redshifts (Barden et al 2005) 30x previous samples (Lilly et al ’98; Simard et al ’99) • FIRES: JHK imaging (0.45”) + 6.000 redshifts (Trujillo et al 2003/5) • Data/Analysis Issues • Understand the (surface brightness) selection function well • Measure sizes at constant rest-frame wavelength >4000A • Consistent tie-in to z~0 data

12. That’s our operative definition of disks == low concentration radial profile Disks to z~1 in GEMSSample SelectionBarden, Rix et al 2005 n<2.5

13. Redshift slices from GEMS Observed color gradients at z~0.5,1.0 • 2-bands HST images in GEMS  check for color-gradients in distant disks • Same gradients as local Correction to rest-frame V is straightforward Difference Rd(mass) and Rd(V) is constant with z

14. GOODS selection box (Ravindranath et al 2004) mv=const Disk Evolution to z~1 from GEMS DataSelection Function

15. 1 mag MV<-20 How did the surface brightness of disk galaxies evolve since z~1? For luminous galaxies, the mean surface brightness has dropped by 1mag over the last 7Gyrs Freeman “law” brighter

21. Evolution of the mean surface mass density of disks since z~1 M*>1010Mo

22. Expected change in surface brightness from the observed stellar population changes Redshift Evolution of the Tully-Fisher RelationBarden, Genzel, Lehnert 2005

23. If r(M) is not f(z)  disks grow inside out

24. Now let’s extend this type of analysis to z~3(FIRES, Trujillo et al 2003/5)

25. At the present, “normal” disk galaxies look completely different in the UV than in the optical M81 “peculiar”, or star-forming ring seen in the UV Older / redder bulge / bar? Zspec=2.9 Are there sizeable (disk?) galaxies at high redshift?(Labbe et al 2003; see also Lowenthal et al 1997)

26. Are the FIRES data deep enough?(FIRES data, Trujillo et al 2003/5)

27. V-band Sizes of FIRES Galaxies compared to SDSS(Trujillo et al 2005;Shen et al 2003)

28. H2/3(z) Size-evolution from z~2.5 to z~0Trujillo et al 2005 At a given (V-band) luminosity, galaxies were about 2.5x smaller at z~2.5 than now. At a given stellar mass, they were only 1.4x smaller than now. Galaxies at high-z were bigger than the naïve halo-scalings lead us to expect!

29. But while NFW halos were denser (within the virial radius) at high-z, they had lower concentrations..(Somerville, Rix, Trujillo, Barden, Bell 2005 in prep.) Simulated disks @ Z=3 Z=1

30. H2/3(z)

31. The Role of Bars Should we expect radial re-distribution due to internal processes? • How prevalent/strong were bars in the past? • Claim (Abraham et al 1999): • Bars only appear at z~0.6 (in HDF) • Analysis of bar frequency in GEMS • algorithmic bar detection • Accounting for (1+z)4 • local comparison sample

32. Bars in GEMSJogee, Rix, et al 2004 • Abundance and strength of bars seems not to have changed since z~1 • In nSersic<2.5 selected galaxies •  tbar x Nreform > fbar x tHubble  bars long-lived

33. Summary • spheroids and disks at high-z (0.5-2.5) seem to live on the same locus in the M*,R,(s) plane • Evolution of this locus in the LV,R plane, reflects changes in stellar mass-to-light ratio This argues for galaxies evolving along those relations. (?) disks grow “inside out”, along R(M)~M1/3 If disks were to grow in mass along with their halos, Rd(M) ~ H-1(z) or H-2/3(z), we would have expected them to be smaller at high-z than observed.

34. Open Issues / Next Steps • Technicalities: • Get more dynamical masses (vz SED masses) • Exploit the potential of IRAC on Spitzer for rest-frame near-IR selection. • Get much more comprehensive merger rate estimates • Avenues • Modelling lagging consideraby behind the wealth of new data • Look-back studies of the “environment’s” role in galaxy evolution. • Host galaxies at high-z (vs normal): a key to understanding BH growth