1. Constraining the History of Star Formation of Early-Type Galaxies Ricardo Schiavon University of Virginia Mini-Workshop, “Galaxy Mergers” STScI, October 4, 2006

2. Collaborators Sandy Faber, Jenny Graves, David Koo, and the DEEP2 collaboration (Lick, UC Berkeley, Caltech, …) Bob O’Connell, Bob Rood (Virginia), and Ruth Peterson (Lick) Jim Rose (North Carolina), Nelson Caldwell (SAO), Stéphane Courteau (Queens), Lauren MacArthur (British Columbia) Beatriz Barbuy, Paula Coelho (IAG/São Paulo), Bruno Castilho (LNA/Brazil)

3. Motivation More than ½ of all the stellar mass in the present day Universe is contained in early- type galaxies Yet, we don’t know how they formed! M49: A Giant Elliptical Galaxy

4. Hierarchical Clustering Monolithic Collapse TIME All stars are old! Old and young stars!

5. Motivation Ultimate Goal: Star formation histories of early-type (E – S0) galaxies No CMDs: Integrated light Stellar Population Synthesis => ages and abundances of stars M49: A Giant Elliptical Galaxy

6. On an Every-week Basis at astro-ph Cimatti et al. (2003) Daddi et al. (2005)

7. The abundance patterns of early-type galaxies is not the same as that of the solar neighborhood => Enrichment by SNe II x SNe Ia Worthey et al. 92Schiavon 2006 Abundance Pattern Early-type Galaxies Stars in the Solar Neighborhood

8. Younger SPs have stronger Balmer lines and weaker metal lines Fundamentals of SP synthesis Effect of Age on SP Spectra

9. More metal-rich SPs have stronger metal lines Fundamentals of SP synthesis Effect of Metallicity on SP Spectra

10. Fundamentals of SP synthesis Because of z ~ 1: the blue spectral region (λ ≤ 4500 Å) needs to be explored Most previous work based on spectra at λ ~ 5000 Å (e.g. Mg2, Hβ) New Models: Schiavon (2006) IMPORTANT

11. Stacked SDSS spectra from Eisenstein et al. (2003) - z ~ 0.15 Subtle Differences  [Fe/H]~0.15  [Mg/H]~0.2  [C/H]~0.25  [N/H]~0.35  [Ca/H] ~ 0.25  Age ~ 2 Gyr

12. DEEP Comparison between measurements taken on Jones (1999) spectra and standard Lick/IDS measurements Line Index Measurements: The Lick/IDS System

13. DEEP Comparison between measurements taken on Jones (1999) spectra and those taken on FAST spectra (Schiavon et al. 2004) Most of the scatter in the previous figure comes from Lick/IDS measurements The “New” Lick System

14. DEEP Blue: [Fe/H] < -0.5 Green: -0.1 < [Fe/H] < -0.5 Red: [Fe/H] > -0.1 R.M.S. of fit: 0.2 Å (giants) and 0.4 Å (dwarfs) Compare with 1.5 Å from Worthey & Ottaviani (1997), which is based on the same spectral library! Fitting Functions

15. Models Age [Fe/H] For Clusters: ages and metallicities For Galaxies: LUMINOSITY- WEIGHTED MEAN ages and metallicities Diagnostic Plots

16. Models The abundance patterns of early-type galaxies is not the same as that of the solar neighborhood Worthey et al. 92Schiavon 2005 Abundance Pattern

17. Models Red: α -enhanced Black: solar-scaled Variable Abundance Patterns

18. DEEP Integrated spectra and UBV magnitudes for 1-solar mass SSP Lick indices for SSPs with 16 < t < 0.1 Gyr, -1.3 < [Fe/H] < +0.3, and variable [Mg/Fe], [C/Fe], [N/Fe], [Ca/Fe], and [O/Fe] Products

19. M67 & M32 47 Tuc: Schiavon et al. (2002)M 67: Schiavon et al. (2004) Cluster Integrated Spectra Don’t believe what I tell you about galaxies if my models do not reproduce cluster data with the necessary accuracy, for the right input parameters

20. M67 & M32 Schiavon (2006, ApJS, submitted) http://www.astro.virginia.edu~/rps7v/Models/Models.html The Models Accurate line indices Accurate stellar parameters Abundance ratios from literature Fitting functions (r.m.s. 1/3 of previous models) Model predictions for SSPs Comparison with cluster data (agreement within 0.1 dex in abundances of Fe,C,N,Mg,Ca, 1-2 Gyr in age) New constraints on SFH of galaxies from comparison with SDSS data

21. DEEP An example: Carbon Solar Scaled Models Variable Abundance Pattern

22. DEEP An example: Carbon [X/Fe] = 0 [C/Fe] = +0.3 Variable Abundance Pattern

23. DEEP An example: Carbon [X/Fe] = 0 [C/Fe] = +0.3 Variable Abundance Pattern

24. DEEP An example: Carbon Variable Abundance Pattern

25. DEEP Another example: Magnesium Variable Abundance pattern

26. DEEP Reality Check: Galactic Clusters

27. M67 & M32 SDSS Red Early-Type Galaxies From Eisenstein et al. (2003)

28. M67 & M32 MrMr MrMr Abundance Pattern [Fe/H] [C/Fe] [Ca/Fe] [N/Fe] [Mg/Fe] Mean Age (Gyr)

29. M67 & M32 SDSS Red Early-Type Galaxies From Eisenstein et al. (2003)

30. M67 & M32 MrMr MrMr Abundance Pattern vs. Environment High density Intermediate density Low density Higher density environments are more N-rich In the field, stars who live in brighter galaxies tend to be younger than those who live in their fainter counterparts

31. M67 & M32 … are substantially younger than those based on Hß Ages According to H 

32. M67 & M32 Different ages according to different Balmer lines

33. M67 & M32 EW errorbars are smaller than symbol size The Balmer “Mismatch”

34. We get it right everywhere! Same for other clusters … in the Case of M67…

35. ~ 3.5 Gyr old with solar metallicity The Age and Metallicity of M67

36. M67 & M32 Match is substantially improved if two- component model is assumed Young component contributes a few to several % by mass, depending on its age (yet another degeneracy!, but see Leonardi+Rose 1996) Hypothesis 1: Age Mix

37. M67 & M32 Cannot fit all Balmer lines at the same time, because of wrong Teff distribution Conclusion: must be present, but contribution to mass budget is probably negligible Hypothesis 2: Metal-poor Population

38. M67 & M32 Don’t match data as well as hypothesis 1, but perhaps acceptable Required specific BS frequency is orders of magnitude higher than seen any where in the Galaxy (see also Trager et al. 2005) Hypothesis 3: Blue Stragglers

39. M67 & M32 Hypothesis 1: Age Mix Conclusion: Red galaxies have undergone prolonged star formation, but substantial fraction of the mass was probably formed before z ~ 1, 1.5 Fit is not perfect: SF history is obviously more complex than two-component model

40. Deep Extragalactic Evolutionary Probe DEEP A survey of distant, faint galaxies with Keck/DEIMOS & HST Goals: formation and evolution of galaxies and large scale structure 60,000 galaxies, 0.7 < z < 1.4, R ~ 5,000 Complete down to R=24, ~ 4 square degrees in the sky Large enough for robust comparison with local counterparts (e.g. SDSS, 2dF) HST/ACS imaging High spectral resolution: galaxy internal kinematics and stellar populations The DEEP2 Project

41. The Sample Initial Sample Color Cut (U-B) > 0.25 No morphologies!!

42. Contamination by late-types is ~ 15% (see Konidaris et al. 2005, in preparation) Emission-Line Cut

43. The Data Distribution of emission-line galaxies in the color-magnitude diagram – more peaked towards the blue end of the red sequence

44. The Stacked Spectra

45. The Data – Final Sample Stacked spectra binned by redshift, color, and luminosity 1160 Red galaxies with low emission- line strength

46. M67 & M32 Red galaxies at z~0.9 have undergone (small amounts of) recent star formation Red galaxies at z~0.9 and z~0.1 are NOT connectetd by lines of passive evolution Results: Ages

47. DEEP2 Stacked Spectra vs. Models

48. M67 & M32 Young and metal- rich: 1.5 Gyr, solar [Fe/H] Results are little sensitive to the choice of [α/Fe] The color sequence seems to be a [Fe/H] sequence Age [Fe/H] Results: Galaxies as a function of Color

49. Results: Carbon abundances M67 & M32 DEEP: [C/Fe] ~ +0.2SDSS: [C/Fe] ~ +0.1

50. Results: Calcium Abundances M67 & M32 DEEP: [Ca/Fe] ~ 0 SDSS: [Ca/Fe] ~ 0

51. Results – Nitrogen Abundances M67 & M32 DEEP: [N/Fe] ~ 0SDSS: [N/Fe] ~ +0.2-0.3

52. DEEP Kelson et al. (2001): CLUSTER early-types evolve passively from a higher z of formation

53. DEEP We can estimate abundances of magnesium, carbon, nitrogen, and calcium, and they might be telling us new details about the history of star formation of early-type galaxies Nitrogen abundances can be constraining the lower limit of the timescale for star formation in early-type galaxies. They are higher in denser environments. Why? Can the strong abundance trends with galaxy mass be telling us something about how (un?) important dry merging is? In the field, stars in giant galaxies seem to be younger, on average, than those in L* galaxies. Interesting result, but beware of H  emission-line infill. Conclusions

54. DEEP On the basis of accurate models and data, one is able to detect 2 nd order effects on Balmer lines This detection allows one to constrain the age spread of stars in red galaxies, revealing the presence of small amounts of young stars and indicating a prolonged history of star formation Analysis of DEEP2 and SDSS data suggests an extended history of star formation for field red galaxies The fact that [Mg/Fe] is enhanced may be telling us that mass fraction in the young component today is very small Conclusions

55. DEEP An idl implementation of the Schiavon (2006) models (see Graves & Schiavon 2006, in preparation) You enter a spectrum, a velocity dispersion (if relevant) and with only two idl commands you’ll get the mean age, [Fe/H], [Mg/Fe], [C/Fe], [N/Fe], [Ca/Fe], and (for assumed [O/Fe]) Z. In just a few minutes!!! And it’s free!!! EZ-Ages E lemental abundances, Z, and Ages It’s really simple! You don’t need to be an idl-freak. Beta-version available upon request. Soon available publicly.

56. The (near) Future Stellar population models in the Mid-UV, from first principles With Peterson, Dorman, O’Connell, Rood, et al.

57. DEEP2 x K20