Stellar Populations of Elliptical Galaxies and Extragalactic Globular Clusters

1. Stellar Populations of Elliptical Galaxies and Extragalactic Globular Clusters A. J. Cenarro IAC Postdoc (JdC)

2. A brief summary of my “astronomical” life… • 1991-1996 – Physics undergrad at Universidad de Zaragoza (UZ) & Universidad Complutense de Madrid (UCM) • 1997-2002 – PhD at the UCM under supervision of Javier Gorgas • Working visits to the University of Durham (Alex Vazdekis; 1998,1999), University of Nottingham (Reynier Peletier; 1998,1999), Universidad Nacional Autónoma de México (Chucho González; 2000)  Background in Stellar Populations of Elliptical Galaxies • 2002-2006 – Teaching Position at the UCM • “Laboratorio de Física” (1); “Estadística” (1); “Técnicas Experimentales en Astrofísica” (4), “Poblaciones Estelares de Galaxias y Cúmulos Estelares” (doctorado) • 2004-2005 – Postdoctoral Position at the UCO/Lick Observatory (UCSC, Santa Cruz, CA) to work with the SAGES group (Jean P. Brodie, Mike Beasley, Jay Strader)  Background in Extragalactic Globular Clusters • 2006-…–Postdoctoral Position at the IAC (Juan de la Cierva)

3. The process of analyzing integrated stellar populations Line Strength Indices Stellar Library Single Stellar Population (SSP) Evolutionary Synthesis Models Observed Stellar Population Atmospheric Parameters Ages, Metallicities, [a/Fe]’s, IMFs, … “Fitting Functions”

4. PhD ThesisUltimate aim: to understand the stellar populations of Es at the near-IR CaT region (a) Development of an Empirical Stellar Library at the Near-IR Spectral Range - Cenarro et al. (2001a,b) - Cenarro et al. (2002) Díaz et al. (1989) ll8348 – 9020 Å FWHM = 1.5 Å  = 0.85 Å /pix 706 stars @ RBS/JKT 06-M8 Spectral Types Flux calibrated

5. PhD ThesisUltimate aim: to understand the stellar populations of Es at the near-IR CaT region (a) Developement of an Empirical Stellar Library at the Near-IR Spectral Range Dwarfs Giants

6. PhD ThesisUltimate aim: to understand the stellar populations of Es at the near-IR CaT region (b) SSP Evolutionary Synthesis Model Predictions Vazdekis et al. (2003)

7. PhD ThesisUltimate aim: to understand the stellar populations of Es at the near-IR CaT region (c) Comparison between SSP Model Predictions and a sample of 35 Es Cenarro et al. (2003) CaT* - logs anticorrelation!!

8. PhD ThesisUltimate aim: to understand the stellar populations of Es at the near-IR CaT region (c) Comparison between SSP Model Predictions and a sample of 35 Es Cenarro et al. (2003) CaT* - logs anticorrelation!!

9. PhD ThesisUltimate aim: to understand the stellar populations of Es at the near-IR CaT region (d) Possible interpretation: s – [Fe/H] – m (dwarf-to-giant ratio) Cenarro et al. (2003)

10. Ongoing Projects on Stellar Population Modeling/Analysis Other Spectral Libraries… - MILES~“1000 estrellas”, flux calibrated @ 2.3 FWHM; λ3500 – 7500 Ǻ(Sánchez-Blázquez et al. 2006; Cenarro et al. 2006, in press; Vazdekis et al. 2007, in prep.)  Next-Generation of SSP models at the optical spectral rangeto overcome the limitations of the Lick/IDS System - K-Band Stellar Library (> 200 stars; Mármol-Queraltó et al. 2006) to understand the behaviour of the CO bands at ~ 2.3 mm in SSPs Line-Strength Index definitions / Fitting functions - For the MILES stellar library: redefining Lick indices + improved age-metallicity indicators + new fitting functions - Using TF’s @ OSIRIS/GTC (ask J. L. Cervantes) Analysing Stellar Population Data: Es and GCs - MAGPOP-ITP (P.I.: G. Kauffman; Stellar Populations of field and cluster dE’s) - Integrated spectroscopy of MW GCs and M31 GCs at the CaT region and the K band - Extragalactic Globular Clusters in Es… (e.g. NGC1407; Cenarro et al. 2006, submitted)

11. What are extragalactic GCs useful for? Constraining different galaxy formation scenarios

12. What do GCs know about galaxy formation? • GCs are fossils of the major star-forming episodes in the Universe(Schweizer 2001) • Confirmed by the detection of YMCs (proto GCs?) in present-day mergers and massive star-forming regions • All galaxies with MV < – 15 host, at least, 1 GC Therefore, GCs may constrain the different scenarios of galaxy formation and assembly. •  When / How did GCs form?

13. Bimodality: a common phenomenon within GC systems NGC 4649 (Larsen et al. 2001) V – I =-1.6-0.5 GC systems follow, in most cases, abimodal color distribution, mainlydriven by metallicity Two GC subpopulations (although still a matter of debate; Yoon et al. 2006): metal poor (MP - blue) and metal-rich (MR - red) • There exist, at least, 2 mechanisms/events of GC formation • Scenarios of galaxy formation must be able to predict the observed bimodality of GC systems. N

14. Classical scenarios of GC formation [1] [3] [2] Classical scenarios: 1.-Major merger(Schweizer 1987, Ashman & Zepf 1992), 2.-In-situ/multiphase dissipational collapse (Forbes et al. 1997), 3.-Accretion(Côté et al. 1998, 2000, 2002), 4.-Hierarchical (Beasley et al. 2002) [4] They all make different predictions on the age difference between both (MP andMR) GC subpopulations Confirming or ruling out the existence of age differences between GC subpopulations is essential to constrain the relative importance of the distinct GC formation scenarios

15. A key observational constrain on GC formation Mean metallicity of GC subpop’s scales with the mass of the host galaxy Strader et al. (2006)

16. New views on GC formation scenarios Given that: • All the previous GC formation scenarios may be valid to some extent: - some young GCs in merger remnants (e.g. NGC3610) - at least 4 MW GCs have been associated to the dSph Saggitarius stream. Could wCen be the nucleus of another accretted dwarf? (Lee et al. 1999) 2. Most extragalactic GCs seem to be old. Even in recent merger remnants, at most < 10% GCs are young or intermediate age (5 – 6 Gyr) z = 13 z = 0 Could it be that the different scenarios happened at high redshift thus blurring their predictions on GC ages?: New scenario (Strader et al. 2005) • MP GCs form at z ~ 10 – 15 in low-mass haloes. GC formation stops by reionization, but massive haloes collapse first (downsizing)  GC metallicity – galaxy mass relationship • MR GCs form in subsequent dissipational merging that forms the host galaxy Reliable age-dating of GC subpopulations is still demanded!!! A systematic study of the GC system ages of different mass E’s needs to be done…

17. Telescope/Intrumentation requirements Luminosity function of GC systems is ~ gaussian and ~universal, peaking at MV0~ -7.4 (V ~ 23.5 at the distance of the Virgo cluster)  Multi-Object Spectroscopy at 8 - 10 m class telescopes! So far at Keck/LIRIS, VLT/VIMOS, Gemini/GMOS… … and now GTC!! OSIRIS-MOS and OSIRIS-TF feasibilities are promising for kinematics and stellar population studies of extragalactic GC systems

18. The GC system of NGC1407: a case study HST/ACS NGC 3610 Merger remnant E Strader et al. (2004) Cenarro et al. (2006, AJ, submitted)

19. NGC1407: The GC spectra HST/ACS 7.5 h @ Keck/LRIS FWHM = 3.7 Ǻ S/N ~ 15 – 95 Ǻ-1 One of the best quality GC spectra observed so far for a galaxy beyond the Local Group!

20. NGC1407 GCs: Mg, Fe and H Balmer index diagnostics

21. NGC1407 GCs: Ages, metallicities and [a/Fe]’s • Input ingredients: • - Lick/IDS system of indices • - SSP models by Thomas et al. (2003, 2004) accounting for different [a/Fe]’s and BHB effects for [Fe/H] < –0.33 dex • Methods: • - c2 procedure by Proctor et al. (2004) - An iterative procedure based on Mg, Fe and H Balmer indices (similar to that in Puzia et al. 2005) Results: - GCs follow a metallicity sequence. Many of them are quite metal-rich - Most GCs are old, but… - There seems to be 3 young GCs (!?) How do we reconcile the existence of young GCs with a 12 Gyr old galaxy!?

22. Young GCs or BHB effects? An example of MW “Second Parameter” GC pair How can we identify BHB stars in the integrated spectra of GCs? The relative contribution of an additionalcomponent of BHB stars (Teff~ 10000 K) to the integrated spectrum is more important at short wavelengths  Hd is more affected than Hb (Schiavon et al. 2004) [Fe/H] ~ –1.5 Teff ~ 10000 K MILES (Sánchez-Blázquez et al. 2006) [Fe/H] ~ –1.5 Hd Hb

23. Young GCs or BHB effects? Young GCs follow the predicted decreasing age trend. On the basis of the BHB diagnostic by Schiavon et al. (2005), they seem to be consistent with hosting BHB stars!! The first “confirmed” detection of BHB extragalactic GCs??

24. C and N in NGC1407 GCs 1 - Extreme CN overabundance 2 - Mg – C correlation (not with CN) does not seem to be due to a Fe underabundance 3 - For MR GCs, N increases a lot at the time that C almost saturates

25. Conclusions 1) GCs do indeed know about galaxy formation although we do not entirely understand what they mean… Age differences between GC subpopulations may constrain the main mechanisms driving their formation (mergers/in-situ/accretions). 2) If GC formation happened at high redshift, age differences between GC subpopulations may be difficult to detect  Reliable age-dating of GC subpopulations needs to be done!! 3) Up to date, most extragalactic GCs seem to be old (> 10 Gyr). Youngish GCs may well be old GCs hosting BHB stars  How important BHBs could be in metal-rich systems? 4) GTC will allow the Spanish Astronomy to face the understanding of galaxy formation and evolution within a general picture of GC formation