Observing the Assembly of Galaxies Hans-Walter Rix Max-Planck-Institute for Astronomy Heidelberg

1. Observing the Assembly of GalaxiesHans-Walter RixMax-Planck-Institute for AstronomyHeidelberg

2. Overview I. The Build-Up of the Stellar Mass in Galaxies II. The Formation and Evolution of Massive Galaxies Thursday May 5, 2:00PM III. The Evolution of (Internal) Galaxy Structure Wednesday May 11, 2:00PM IV. Archeo-Cosmology in the Local Group Friday, May 13, 2:00PM

3. I. The Build-Up of Stellar Mass • Casting the problem into specific questions • Diagnostic Tools • A brief survey of surveys • Estimating the star-formation rate = f(z) • Estimating the stellar mass density = f(z) • Results

4. 1. Re-phrasing “the build-up of stellar mass” • What is <SFR(z)> and <r*(z) >? • What epoch encloses the formation of most stars? • How to best measure <SFR (z) > and <r*(z) > ? • How much important are mergers in triggering SF and in setting the present-day mass function? • What are the expectations from models?

5. 2. Diagnostic tools for star-formation rates and stellar masses • Star formation rate estimates are based on UV luminosity produced by hot, massive, short-lived stars • Observe the UV • Observe Ha • Observe absorbed UV flux, re-radiated by dust in thermal IR ! LIR(re-radiated) >> LUV(escaped) ! • Mtot estimate is based on stars >10Mo, which are small fraction of Mtot Kroupa 2002

6. Starlight and Re-processed Starlight Single-age, dust-free stellar population Devriend et al 2000

7. Redshift ground Herschel (2007) Spitzer SED of an ageing stellar population of solar metalicity with dust

8. f(24mm) vs Lbol Papovich and Bell 2003 Given that Spitzer can only observe well at 24 mm, what are the bolometric corrections?

9. Mass measurements in cosmologically distant galaxies • Dynamics: • OK to z~1, but quite expensive. • Very limited spatial resolution conceptually problematic • Currently not feasible for most galaxies z>1.5 • Clustering: • Measures halo mass, not stellar mass • M* = L x (M/L)* with M/L from SEDs

10. tstars = [Gyrs] B K Bell and de Jong 2001 Stellar Masses from Spectral Energy Distributions • Near-degeneracy of age, metallicity and dust • Source of despair or opportunity? Optical/near-IR spectra of galaxies are a nearly 1D sequence

11. Mapping one or few integrated galaxy colors to • age • dust extinction • metallicity is poor! • Mapping (optical -- across 4000A break) color to M/L should be robust!

12. M/L from Colors? Compare to Mdyn!Van der Wel, Franx, can Dokkum and Rix, 2004 at z~1

13. Look-back Galaxy Surveys: Desiderata • Select SFR surveys by SFR, and mass surveys by stellar mass • SFR: assure most of the intense star-burst are not missing due to dust • Stellar mass: select galaxies lobs > (1+z) 4000A break • Number of galaxies as a function of • Epoch  redshift (few %) • Luminosity/stellar mass • Color/stellar age 1,000 – 10,000 galaxies • Measure galaxy sizes/internal structure ~0.3” resolution • Either Nfield >> 1 or qfield > 2xcorrelation length ~10’

14. A Survey Survey

16. Z MB Wavelength [nm] COMBO-17Wolf, Meisenheimer, Rix et al. 01/03Heidelberg, Oxford,Potsdam,Edinburgh • 3 fields @ 30’x30’ • 17 filters to mr~23.6 • ~10.000 redshifts (1.5%)+ SEDs per field

17. Comparison of COMBO-17 with VIMOS Spectra(data from Le Fevre et al 2004)

18. A quick Tour through Redshift Space Abell 901 S11 (random) GEMS(CDFS)

20. 0.65<z<0.75 Stellar Masses from the COMBO-17 SurveyBorch, Rix, Meisenheimer et al 2005 • Stellar masses to z~1 can be estimated for 10.000s of galaxies • Flux limit (R-band) is VERY different from mass limits.

21. FIRES: FaintInfra-Red-Extragalactic-Survey ultra-deep VLT survey *HDF-south 100 hours in JHK FWHM=0.45” *MS1054: 5xlarger area 25 hours in JHK per pointing Franx, Rix, Rudnick, Labbe, van Dokkum, Foerster-Schreiber, Trujillo, Moorwood, et al. 2001-2005 Selecting and studying galaxies z>2 in their rest-frame optical bands

22. Not a Ly-break!! Just a red SED

23. What kind of galaxies are found in such a search? • Galaxies without many (really) young stars won’t be found by their Ly-break or their sub-mm dust emission. • Ditto for galaxies with significant dust extinction that are not powerful enough for a sub-mm detection. • Remember: both UV searches (dust) and sub-mm searches (fainter galaxies) have ~10 corrections to get total SFR

24. SED fits for DRGs Near-IR selected UV selected Förster-Schreiber, Franx, Rix et al; FIRES

25. Förster-Schreiber, Rix et al 2005; FIRES Improving Mass, SFR and Av Estimates at z~2.5 through IRAC (3.6mm-8mm) dataLabbe, Franx, Rix et al 2005

26. Comparing dynamical (?) with SED masses Van Dokkum, Franx, Rix, et al. 2004

27. Results I: Cosmic Star-Formation Rate

28. Stacking galaxy classes (z,L) from COMBO-17 and measuring the 24mm flux SFR’s from thermal-IR flux 0<z<1Zheng, Rix, Rieke, Bell et al 2004

29. LIR/LUV = f(SFR) @ all z,Lopt Local relation SFR’s from thermal-IR flux 0<z<1Zheng, Rix, Rieke, Bell et al 2004 • Through stacking, Spitzer’s (single source) confusion limit can be beat by >10 to <10mJy • IR flux dominates in all galaxies (to 3% of L*) to z~1.2; • large majority of UV photons absorbed. • Mean LIR/LUV drops with galaxy luminosity  faint galaxies contribute hardly to SF integral • “Correction” seems to be a function of (absolute) SFR only • Insensitive to stellar luminosity, redshift

30. State of Affairs: Star-fomration rate Borch, Rix, Meisenheimer et al 2005

31. Why the drop of the SFR since z~1?or In what type of galaxies did stars form back then?

32. UV-to-optical flux (M280nm – V) Whence the UV flux at z~0.7?j280 (z~0.7) ~ 4 x j280nm (now) Wolf, Bell, Rix et al 2004 0.65<z<0.75 Pick f(2800A) as a proxy for young stars (t<tdyn) [not necessarily true in massive, old systems] Explore “morphology” of galaxies that give rise to these photons Subjective – use 6 eyes [Morphologies from GEMS, see Thursday] UV luminous “blue”

33. z~0.75 Normal spirals Interacting/Peculiar UV-light contribution by Galaxy type at z~0.75 • At MV>-19 and z~0.75 • ½ the flux comes from seemingly normal spirals • 20% from visibly interacting systems • only minority of UV flux from manifestly interacting systems at z~0.75 • drop in (major) merger rate not cause of SFR drop

34. Results II:Evolution of the Stellar Mass Density with Redshift

35. COMBO-17 survey; 30,000 galaxies Present-day stellar mass function The Evolution of the Stellar Mass Function over the Last 7 Gyrs Mean stellar mass Build-Up Borch, Meisenheimer, Rix, Bell et al 2005, COMBO-17

36. Where is the stellar mass at z=2-3.5?DRGs (“distant red galaxies”) vs Ly-Break Galaxies Distant red galaxies likely dominate the mass budget

37. Borch, Meisenheimer, Rix et al 2005 <r*(z)>: State of Affairs

38. Borch et al 2005 …half the mass since z~1.5…

39. Borch, Meisenheimer, Rix et al 2005 Putting it together

40. Summary • Waning SFR not a consequence of waning major mergers • Waning cold gas supply • SED-based stellar mass estimates now available for 1000’s of galaxies to z~3 • Need to observe at least to lrest>4000A • Available testing against dynamics OK • “Distant red galaxies”, between Ly-break and sub-mm galaxies, may contain the bulk of stellar mass 2<z<3.5 • Found through near-IR surveys • Quite frequent objects with SFR x tSFR ~1010-11M • <r*(z) > can be traced from z~3.5 to 0 • enclosing ~90% of all stars formed • Integral over SFR estimate agrees with <r*(z) > to < 2 • Assuming diet-Salpeter IMF (e.g. Kroupa 2002) • Leaves not much room for overlooked SFR

41. Where do we go from here? • Role of merging in the build-up of the galaxy mass function is observationally barely constrained • Comprehensive linkeage of SED-based and dynamical masses • Beat field-to-field variations at z>2 • Relate stellar masses at different z to halo masses • Lensing, clustering