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

A brief summary of my “astronomical” life… – Physics undergrad at Universidad de Zaragoza (UZ) & Universidad Complutense de Madrid (UCM) – Physics undergrad at Universidad de Zaragoza (UZ) & Universidad Complutense de Madrid (UCM) – PhD at the UCM under supervision of Javier Gorgas – 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) 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 – Teaching Position at the UCM – Teaching Position at the UCM “Laboratorio de Física” (1); “Estadística” (1); “Técnicas Experimentales en Astrofísica” (4), “Poblaciones Estelares de Galaxias y Cúmulos Estelares” (doctorado) “Laboratorio de Física” (1); “Estadística” (1); “Técnicas Experimentales en Astrofísica” (4), “Poblaciones Estelares de Galaxias y Cúmulos Estelares” (doctorado) – Postdoctoral Position at the UCO/Lick Observatory (UCSC, Santa Cruz, CA) to work with the SAGES group (Jean P. Brodie, Mike Beasley, Jay Strader) – 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) 2006-… – Postdoctoral Position at the IAC (Juan de la Cierva)

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

PhD Thesis Ultimate aim: to understand the stellar populations of Es at the near-IR CaT region 706 RBS/JKT 06-M8 Spectral Types Flux calibrated  8348 – 9020 Å 8348 – 9020 Å FWHM = 1.5 Å  = 0.85 Å /pix (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)

PhD Thesis Ultimate 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

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

PhD Thesis Ultimate 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* - log  anticorrelation!!

PhD Thesis Ultimate 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* - log  anticorrelation!!

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

Ongoing Projects on Stellar Population Modeling/Analysis Other Spectral Libraries… - MILES ~“1000 estrellas”, flux 2.3 FWHM; λ 3500 – 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 range to 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  m in SSPs Line-Strength Index definitions / Fitting functions - For the MILES stellar library: redefining Lick indices + improved age-metallicity indicators + new fitting functions - Using 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)

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

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

Bimodality: a common phenomenon within GC systems GC systems follow, in most cases, a bimodal color distribution, mainly driven by metallicity  Two GC subpopulations (although still a matter of debate; Yoon et al. 2006): metal poor (MP - blue) and metal-rich (MR - red) GC systems follow, in most cases, a bimodal color distribution, mainly driven 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. NGC 4649 (Larsen et al. 2001) V – I = N

Classical scenarios of GC formation 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) 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 They all make different predictions on the age difference between both (MP and MR) GC subpopulations [1] [2] [4] [3]

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)

Given that: 1.All the previous GC formation scenarios may be valid to some extent: - some young GCs in merger remnants (e.g. NGC3610) - some young GCs in merger remnants (e.g. NGC3610) - at least 4 MW GCs have been associated to the dSph Saggitarius stream. Could  Cen be the nucleus of another accretted dwarf? (Lee et al. 1999) - at least 4 MW GCs have been associated to the dSph Saggitarius stream. Could  Cen 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) New views on GC formation scenarios Could it be that the different scenarios happened at high redshift thus blurring their predictions on GC ages?: New scenario ( Strader et al ) 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 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 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… z = 13 z = 0

Telescope/Intrumentation requirements Luminosity function of GC systems is ~ gaussian and ~universal, peaking at M V 0 ~ -7.4 (V ~ 23.5 at the distance of the Virgo cluster)  Multi-Object Spectroscopy at 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

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

NGC1407: The GC spectra HST/ACS 7.5 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!

NGC1407 GCs: Mg, Fe and H Balmer index diagnostics

NGC1407 GCs: Ages, metallicities and [  /Fe]’s Input ingredients: - Lick/IDS system of indices - SSP models by Thomas et al. (2003, 2004) accounting for different [  /Fe]’s and BHB effects for [Fe/H] < –0.33 dex Methods: -  2 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!?

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

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?? Age-H  (Gyr) Age-H  (Gyr) Age-H  /H  (Gyr) #1 6.0 ± ± 1.6 ~ 1.0 # ± ± 1.3 ~ 3.5 #3 9.2 ± ± 2.6 ~ 6.0

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

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