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

Stellar Populations of Stellar Populations of Elliptical Galaxies and Elliptical Galaxies and Extragalactic Globular Extragalactic Globular

ClustersClusters

A. J. CenarroA. J. Cenarro IAC Postdoc (JdC)IAC Postdoc (JdC)

A brief summary of my “astronomical” life…A brief summary of my “astronomical” life…

1991-19961991-1996 – – Physics undergradPhysics undergrad at Universidad de Zaragoza (UZ) & at Universidad de Zaragoza (UZ) & Universidad Complutense de Madrid (UCM)Universidad Complutense de Madrid (UCM)

1997-20021997-2002 – – PhD at the UCMPhD at the UCM under supervision of under supervision of Javier GorgasJavier Gorgas Working visits to the University of Durham (Working visits to the University of Durham (Alex VazdekisAlex Vazdekis; 1998,1999), ; 1998,1999),

University of Nottingham (University of Nottingham (Reynier PeletierReynier Peletier; 1998,1999), Universidad ; 1998,1999), Universidad Nacional Autónoma de México (Nacional Autónoma de México (Chucho GonzálezChucho González; 2000); 2000)

Background in Stellar Populations of Elliptical GalaxiesBackground in Stellar Populations of Elliptical Galaxies

2002-20062002-2006 – – Teaching Position at the UCMTeaching Position at the UCM ““Laboratorio de FísicaLaboratorio de Física” ” (1)(1); “; “EstadísticaEstadística” ” (1)(1); “; “Técnicas Experimentales Técnicas Experimentales

en Astrofísicaen Astrofísica” ” (4)(4), “, “Poblaciones Estelares de Galaxias y Cúmulos Poblaciones Estelares de Galaxias y Cúmulos EstelaresEstelares” ” (doctorado)(doctorado)

2004-20052004-2005 – – Postdoctoral Position at the UCO/Lick ObservatoryPostdoctoral Position at the UCO/Lick Observatory (UCSC, (UCSC, Santa Cruz, CA) to work with the SAGES group (Santa Cruz, CA) to work with the SAGES group (Jean P. BrodieJean P. Brodie, , Mike Mike Beasley, Jay StraderBeasley, Jay Strader))

Background in Extragalactic Globular ClustersBackground in Extragalactic Globular Clusters

2006-…2006-… –– Postdoctoral Position at the IAC (Postdoctoral Position at the IAC (Juan de la CiervaJuan de la Cierva))

Stellar Stellar LibraryLibrary

Atmospheric Atmospheric ParametersParameters

Line Strength Line Strength IndicesIndices

““Fitting Fitting Functions”Functions”

Single Stellar Population Single Stellar Population (SSP) Evolutionary (SSP) Evolutionary Synthesis ModelsSynthesis Models

Observed Observed Stellar Stellar

PopulationPopulation

Ages, Metallicities, Ages, Metallicities, [[/Fe]’s, IMFs, …/Fe]’s, IMFs, …

The process of analyzing integrated stellar The process of analyzing integrated stellar populationspopulations

PhD ThesisPhD ThesisUltimate aim: to understand the stellar populations of Es at the near-IR CaT Ultimate aim: to understand the stellar populations of Es at the near-IR CaT

regionregion

706 stars @ RBS/JKT06-M8 Spectral Types

Flux calibrated

8348 – 9020 Å8348 – 9020 Å

FWHM =FWHM = 1.5 Å 1.5 Å

== 0.85 Å /pix 0.85 Å /pix

(a) Development of an Empirical Stellar Library at the Near-IR Spectral (a) Development of an Empirical Stellar Library at the Near-IR Spectral RangeRange

- Cenarro et al. (2001a,b)- Cenarro et al. (2002)

Díaz et al. (1989)


regionregion(a) Developement of an Empirical Stellar Library at the Near-IR Spectral (a) Developement of an Empirical Stellar Library at the Near-IR Spectral RangeRange

Dwarfs Giants


regionregion(b) SSP Evolutionary Synthesis Model Predictions(b) SSP Evolutionary Synthesis Model Predictions Vazdekis et al. (2003)

09.023.2log C,0

0.20)(-0.68,y Metallicit

Gyr) 18 - (5 Age

1.3)( IMFSalpeter


regionregion(c) Comparison between SSP Model Predictions and a sample of 35 Es (c) Comparison between SSP Model Predictions and a sample of 35 Es

Cenarro et al. (2003)

CaT* - log anticorrelation!!

09.023.2log C,0


regionregion(c) Comparison between SSP Model Predictions and a sample of 35 Es (c) Comparison between SSP Model Predictions and a sample of 35 Es

0.20)(-0.68,y Metallicit

3.3)-(0.3 Slope IMF

age old Fixed


CaT* - log anticorrelation!!


regionregion(d) Possible interpretation: (d) Possible interpretation: – [Fe/H] – – [Fe/H] – (dwarf-to-giant ratio) (dwarf-to-giant ratio)


Ongoing Projects on Stellar Population Modeling/AnalysisOngoing Projects on Stellar Population Modeling/Analysis

Other Spectral Libraries…Other Spectral Libraries…

- - MILESMILES ~~“1000 estrellas”, flux calibrated @ 2.3 FWHM; “1000 estrellas”, flux calibrated @ 2.3 FWHM; λλ 3500 – 7500 3500 – 7500 ǺǺ (Sánchez-Blázquez et al. 2006; Cenarro et al. 2006, in press; Vazdekis et (Sánchez-Blázquez et al. 2006; Cenarro et al. 2006, in press; Vazdekis et al. 2007, in prep.) al. 2007, in prep.) Next-Generation of SSP models at the optical Next-Generation of SSP models at the optical spectral rangespectral range to overcome the limitations of the Lick/IDS Systemto overcome the limitations of the Lick/IDS System- - K-Band Stellar LibraryK-Band Stellar Library (> 200 stars; Mármol-Queraltó et al. 2006) to (> 200 stars; Mármol-Queraltó et al. 2006) to understand the behaviour of the CO bands at understand the behaviour of the CO bands at ~ ~ 2.3 2.3 m in SSPsm in SSPs

Line-Strength Index definitions / Fitting functionsLine-Strength Index definitions / Fitting functions

- For the MILES stellar library: redefining Lick indices + improved age-- For the MILES stellar library: redefining Lick indices + improved age-metallicity indicators + new fitting functionsmetallicity indicators + new fitting functions- Using - Using TF’s @ OSIRIS/GTCTF’s @ OSIRIS/GTC (ask J. L. Cervantes) (ask J. L. Cervantes)

Analysing Stellar Population Data: Es and GCsAnalysing Stellar Population Data: Es and GCs

- - MAGPOP-ITPMAGPOP-ITP (P.I.: G. Kauffman; Stellar Populations of field and cluster (P.I.: G. Kauffman; Stellar Populations of field and cluster dE’s)dE’s)- - Integrated spectroscopyIntegrated spectroscopy of of MW GCsMW GCs and and M31 GCsM31 GCs at the CaT at the CaT region and the K bandregion and the K band- - Extragalactic Globular Clusters in Es… Extragalactic Globular Clusters in Es… (e.g. NGC1407; Cenarro et (e.g. NGC1407; Cenarro et al. 2006, submitted)al. 2006, submitted)

Constraining Constraining different galaxy different galaxy

formation formation scenariosscenarios

What are extragalactic GCs useful for?What are extragalactic GCs useful for?

What do GCs What do GCs knowknow about galaxy formation? about galaxy formation?

• GCs areGCs are fossils fossils of the of the major star-forming episodes in major star-forming episodes in the Universethe Universe (Schweizer 2001)(Schweizer 2001)• Confirmed by the detection of YMCs (proto GCs?) in Confirmed by the detection of YMCs (proto GCs?) in present-day mergers and massive star-forming regionspresent-day mergers and massive star-forming regions• All galaxies with All galaxies with MMVV < < –– 15 host, at least, 1 GC 15 host, at least, 1 GC

Therefore, GCs may Therefore, GCs may constrain the different scenarios constrain the different scenarios of galaxy formation and assemblyof galaxy formation and assembly..

When / HowWhen / How did GCs form? did GCs form?

Bimodality: a common phenomenon within GC Bimodality: a common phenomenon within GC systemssystems

GC systems follow, in most cases, aGC systems follow, in most cases, a bimodal bimodal color color distribution, mainlydistribution, mainly driven by metallicitydriven by metallicity Two GC Two GC

subpopulations (although still a matter of debate;subpopulations (although still a matter of debate; Yoon et al. Yoon et al. 2006)2006): metal poor: metal poor ( (MP - blueMP - blue) ) and metal-richand metal-rich ( (MR - redMR - red))

There exist, at least, There exist, at least, 2 mechanisms/events of GC formation2 mechanisms/events of GC formation Scenarios of galaxy formation Scenarios of galaxy formation mustmust be able to predict the be able to predict the

observed bimodality of GC systems.observed bimodality of GC systems.

NGC 4649 (Larsen et al. 2001)

V – I = -1.6 -0.5

N

Classical scenarios of GC formation Classical scenarios of GC formation Classical scenarios: 1.-Classical scenarios: 1.-Major mergerMajor merger (Schweizer 1987, Ashman & Zepf (Schweizer 1987, Ashman & Zepf 1992), 1992), 2.-2.-In-situ/multiphase dissipational collapse In-situ/multiphase dissipational collapse (Forbes et al. 1997), (Forbes et al. 1997), 3.-3.-AccretionAccretion (Côté et al. 1998, 2000, 2002), (Côté et al. 1998, 2000, 2002), 4.-4.-Hierarchical Hierarchical (Beasley (Beasley et al. 2002)et al. 2002)

Confirming or ruling out the existence of Confirming or ruling out the existence of age differencesage differences between GC subpopulations is essential to constrain the between GC subpopulations is essential to constrain the

relative importance of the distinct GC formation scenariosrelative importance of the distinct GC formation scenarios

They all make different predictions on the They all make different predictions on the age differenceage difference between both (between both (MP MP andand MRMR) ) GC subpopulationsGC subpopulations

[1][2]

[4]

[3]

A key observational constrain on GC A key observational constrain on GC formationformation

Mean metallicity of GC subpop’s scales with the mass of the Mean metallicity of GC subpop’s scales with the mass of the host galaxy host galaxy

Strader et al. (2006)

Given that:Given that:1.1. All the previous GC formation scenarios may be valid to some extentAll the previous GC formation scenarios may be valid to some extent:: - some young GCs in - some young GCs in mergermerger remnants (e.g. NGC3610) remnants (e.g. NGC3610) - at least 4 MW GCs have been associated to the dSph Saggitarius stream. Could - at least 4 MW GCs have been associated to the dSph Saggitarius stream. Could

Cen be the nucleus of another Cen be the nucleus of another accrettedaccretted dwarf? dwarf? (Lee et al. 1999)(Lee et al. 1999)2. Most extragalactic GCs seem to be old.2. Most extragalactic GCs seem to be old. Even in recent merger remnants, at Even in recent merger remnants, at

most < 10% GCs are young or intermediate age (5 – 6 Gyr)most < 10% GCs are young or intermediate age (5 – 6 Gyr)

New views on GC formation scenariosNew views on GC formation scenarios

Could it be that the different scenarios Could it be that the different scenarios happened at high redshift thus blurring their happened at high redshift thus blurring their

predictions on GC ages?:predictions on GC ages?:New scenario (New scenario (Strader et al. 2005Strader et al. 2005))

• MPMP GCs form at z GCs form at z ~ ~ 10 – 15 in low-mass 10 – 15 in low-mass haloes. GC formation stops by reionization, haloes. GC formation stops by reionization, but massive haloes collapse first (but massive haloes collapse first (downsizingdownsizing) ) GC metallicity – galaxy mass relationshipGC metallicity – galaxy mass relationship• MRMR GCs form in subsequent dissipational GCs form in subsequent dissipational merging that forms the host galaxymerging that forms the host galaxy

Reliable age-dating of GC subpopulations is still Reliable age-dating of GC subpopulations is still demanded!!!demanded!!!

A systematic study of the GC system ages of different mass E’s A systematic study of the GC system ages of different mass E’s needs to be done…needs to be done…

z = 13 z = 0

Telescope/Intrumentation requirementsTelescope/Intrumentation requirementsLuminosity functionLuminosity function of GC systems is of GC systems is ~~ gaussian and gaussian and ~~universal,universal, peaking at peaking at MMVV

00 ~ -7.4~ -7.4 (V ~ 23.5 at the distance of the Virgo cluster) (V ~ 23.5 at the distance of the Virgo cluster) Multi-Object Spectroscopy at 8 - 10 m class telescopes!Multi-Object Spectroscopy at 8 - 10 m class telescopes! So far at So far at Keck/LIRIS, VLT/VIMOS, Gemini/GMOS…Keck/LIRIS, VLT/VIMOS, Gemini/GMOS…

… … and now GTC!! and now GTC!!

OSIRIS-MOSOSIRIS-MOS and and OSIRIS-TFOSIRIS-TF feasibilities are promising for feasibilities are promising for

kinematics and stellar kinematics and stellar population studies of population studies of

extragalactic GC systemsextragalactic GC systems

NGC 3610NGC 3610Merger remnant EMerger remnant EStrader et al. (2004)Strader et al. (2004)

The GC system of NGC1407: a case studyThe GC system of NGC1407: a case studyHST/ACSHST/ACS

Cenarro et al. (2006, AJ, submitted)

NGC1407: The GC spectraNGC1407: The GC spectraHST/ACS

7.5 h @ 7.5 h @ Keck/LRISKeck/LRIS

FWHM = 3.7 FWHM = 3.7 ǺǺ

S/N ~ 15 – 95 S/N ~ 15 – 95 ǺǺ-1-1

One of the best One of the best quality GC quality GC spectra spectra observed so far observed so far for a galaxy for a galaxy beyond the beyond the Local Group!Local Group!

NGC1407 GCs: Mg, Fe and H Balmer index NGC1407 GCs: Mg, Fe and H Balmer index diagnosticsdiagnostics

NGC1407 GCs: Ages, metallicities and NGC1407 GCs: Ages, metallicities and [[/Fe]’s/Fe]’s

Input ingredients:Input ingredients:- Lick/IDS system of indices- Lick/IDS system of indices- SSP models by - SSP models by Thomas et al. Thomas et al. (2003, 2004)(2003, 2004) accounting for accounting for different different [[/Fe]’s and BHB effects /Fe]’s and BHB effects for [Fe/H] < –0.33 dexfor [Fe/H] < –0.33 dex

Methods:Methods:

- - 22 procedure by procedure by Proctor et al. Proctor et al. (2004)(2004)- An iterative procedure based on - An iterative procedure based on Mg, Fe and H Balmer indices Mg, Fe and H Balmer indices (similar to that in (similar to that in Puzia et al. 2005Puzia et al. 2005))

Results:Results:- GCs follow a metallicity sequence. - GCs follow a metallicity sequence. Many of them are Many of them are quite metal-richquite metal-rich- Most GCs are - Most GCs are oldold, but…, but…- There seems to be - There seems to be 3 young GCs3 young GCs (!?)(!?)

How do we reconcile the existence of How do we reconcile the existence of youngyoung GCs with a 12 Gyr old galaxy!? GCs with a 12 Gyr old galaxy!?

Young GCs or BHB effects?Young GCs or BHB effects?

[Fe/H] ~ –1.5

[Fe/H] ~ –1.5

How can we identify BHB stars in How can we identify BHB stars in the the integratedintegrated spectra of GCs? spectra of GCs?The relative contribution of an The relative contribution of an additionaladditional component of BHB component of BHB stars (stars (TTeffeff ~ 10000 K) to the ~ 10000 K) to the integrated spectrum is more integrated spectrum is more important at short wavelengths important at short wavelengths HH is more affected than H is more affected than H (Schiavon et al. 2004)(Schiavon et al. 2004)

HH

An example ofAn example ofMW “Second Parameter” GC pairMW “Second Parameter” GC pair

TTeffeff ~ 10000 K ~ 10000 KMILESMILES

(Sánchez-Blázquez et al. 2006)(Sánchez-Blázquez et al. 2006)

Young GCs or BHB effects?Young GCs or BHB effects?

YoungYoung GCs follow the GCs follow the predicted decreasing predicted decreasing age trend. age trend. On the On the basis of the BHB basis of the BHB diagnostic by diagnostic by Schiavon et al. Schiavon et al. (2005),(2005),they seem to be they seem to be consistent with consistent with hosting BHB stars!!hosting BHB stars!!

The first “confirmed” The first “confirmed” detection of BHB detection of BHB extragalactic GCs?? extragalactic GCs??

Age-HAge-H(Gyr)(Gyr)

Age-Age-HH

(Gyr)(Gyr)

Age-HAge-H//HH(Gyr)(Gyr)

##11

6.0 6.0 ± ± 3.83.8 2.8 2.8 ± ± 1.61.6

~~ 1.0 1.0

##22

10.8 10.8 ± ± 2.82.8

5.1 5.1 ± ± 1.31.3

~ ~ 3.53.5

##33

9.2 9.2 ± ± 2.92.9 6.6 6.6 ± ± 2.62.6

~~ 6.0 6.0

C and N in NGC1407 GCsC and N in NGC1407 GCs

1 - Extreme 1 - Extreme CNCN overabundanceoverabundance2 - 2 - Mg – CMg – C correlation correlation (not with CN) does (not with CN) does not seem to be due not seem to be due to a Fe to a Fe underabundanceunderabundance3 - For 3 - For MRMR GCs, GCs, NN increases a lot at the increases a lot at the time that time that CC almost almost saturatessaturates

ConclusionsConclusions

1)1) GCs GCs do indeed knowdo indeed know about galaxy formation about galaxy formation although we although we do not entirely understand what they mean… do not entirely understand what they mean… Age Age differences differences between GC subpopulations may between GC subpopulations may constrain the constrain the main mechanisms driving their formationmain mechanisms driving their formation (mergers/in-situ/accretions).(mergers/in-situ/accretions).

2)2) If GC formation happened at high redshift,If GC formation happened at high redshift, age differences age differences between GC subpopulations may be difficult to detectbetween GC subpopulations may be difficult to detect Reliable age-dating of GC subpopulations needs to be Reliable age-dating of GC subpopulations needs to be

done!!done!!

3)3) Up to date, most extragalactic GCsUp to date, most extragalactic GCs seem to be seem to be old old (> 10 (> 10 Gyr). Gyr). YoungishYoungish GCs may well be GCs may well be old GCs hosting BHB stars old GCs hosting BHB stars How important BHBs could be in metal-rich systems? How important BHBs could be in metal-rich systems?

4) 4) GTC will allow the Spanish Astronomy to face the GTC will allow the Spanish Astronomy to face the understanding of galaxy formation and evolution within a understanding of galaxy formation and evolution within a general picture of GC formationgeneral picture of GC formation

Documents

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