Constraining the History of Star Formation of Early-Type Galaxies

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 • 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

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

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

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

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

8. DEEP The “New” Lick System 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

9. DEEP Fitting Functions 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!

10. M67 & M32 Cluster Integrated Spectra 47 Tuc: Schiavon et al. (2002) M 67: Schiavon et al. (2004) 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

11. M67 & M32 The Models Schiavon (2006, ApJS, submitted) http://www.astro.virginia.edu~/rps7v/Models/Models.html • 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

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

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

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

15. M67 & M32 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 Mr Mr

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

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

18. DEEP The DEEP2 Project Deep Extragalactic Evolutionary Probe • 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

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

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

21. M67 & M32 Results: Ages • 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

22. DEEP2 Stacked Spectra vs. Models

23. M67 & M32 Results: Galaxies as a function of Color • 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]

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

25. DEEP Conclusions • 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.

26. DEEP Conclusions • On the basis of accurate models and data, one is able to detect 2nd 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