Globular Clusters in Early type Galaxies Jean P. Brodie UCO/Lick Observatory University of California Santa Cruz Study of Astrophysics of Globular clusters in Extragalactic Systems SAGES My talk will focus on how we might use globular clusters to constrain galaxy formation in a lambda CDM universe, under the understanding that GCs are good tracers of the major star forming episodes in a galaxy’s history. I want to draw your attention to the members of the SAGES group who are present at this conference as their presentations are complementary to the work I’ll be describing. We have an ongoing recruitment for a SAGES postdoc so if you think you might be interested you can let me know. M.Beasley (IAC), J.Cenarro (UCSC/Madrid), D.Forbes (Swinburne), K.Forde (UCSC), S.Larsen (ESO), L.Spitler (Swinburne), J.Strader (UCSC)

GC/Galaxy Formation Models 1. Formation of ellipticals/GCs in mergers (Schweizer 1987, Ashman & Zepf 1992) 2. In situ/multi-phase collapse (Forbes, Brodie & Grillmair 1997) 3. Accretion/stripping (Cote’ et al. 1998) 4. Hierarchical merging (Beasley et al. 2002) 2 & 4 require (temporary) truncation of GC formation at high redshift I was flattered that Paul liked this slide enough to use it! I am putting this up mostly just for historical context. These scenarios(list) were suggested to explain bimodality and elements of each of them have survived to the present. They served to focus our thinking on what observables would be most useful in determinging the relative importance of these models and thus give us some insight into how and when galaxies assembled. Notice though that it has been clear for some time that we appear to need to truncate GC formation at high redshift in order to reproduce the observed bimodality. z

Spirals vs Ellipticals Surveys of early type galaxies: WFPC2 and ACS esp.Virgo Cluster Survey (Cote et al) Average blue peak color (V–I)o=0.95, (g–z)=0.95 Average red peak color (V–I)o=1.18, (g–z)=1.40 (Larsen et al 2001; Kundu & Whitmore 2001, Peng et al 2006, Strader et al 2006)  [Fe/H]~ – 1.5, –0.6 Milky Way Peaks at [Fe/H] ~ – 1.5 and – 0.6 (Zinn 1985) MW GCs are essentially all old Also in M 31 Milky Way

Superglob! Combining our best spectro data (S/N >30) we find both red and blue sub-pops are ~12 Gyr old, coeval to within the errors Most of the star formation in massive early-type galaxies happened at z > ~2 Lower mass galaxies/lower density environments may have larger fraction of young GCs, consistent with downsizing Puzia et al (2005) Strader, Brodie, Cenarro Beasley & Forbes (2005) Everyone realized that figuring out the ages of the red and blue GCs was vitally important for differentiating between the formation scenarios and determining when the bulk of the galaxy forming action took place. This plot summarizes more than a decade’s worth of effort with the Keck 10m telescope to determine accurate spectroscopic ages for both the red and the blue GCs.

Ages: NGC 1407 Cenarro et al (2006) – see poster All GCs old, outliers due to BHB effects Let me give you an example of some really excellent data which show clearly the old ages of both the blue AND the red GCs. I refer you to Javier Cenarro’s poster for more details. Now the fact most GCs are old suggest that you can’t form the bulk of the red GCs in gaseous mergers in the recent past.

Specific Frequencies Tblue Larger relative numbers of MP GCs with increasing galaxy mass Rhode, Zepf & Santos (2005) Could be flat for spirals Argues against (recent) major merger model for Es in high density environments Tred

Correlations with Parent Galaxy Properties Strader, Brodie & Forbes (2004) Colors (metallicities) of both reds and blues correlate with galaxy mass Brodie & Strader (2006) Red GC and galaxy color relations have same slope  Red GCs and galaxy stars formed together Spirals fit trends What does blue relation tell us about accretion/major merger scenarios? Constraints on Hierarchical Merging Also Larsen et al 2001, Lotz et al 2004 Peng et al 2006, Strader et al 2006

CDM N-body simulations suggest that dark matter halos “sitting” on top of large overdensities collapse first (z>10) The majority of these halos combine to form massive galaxies at z=0 Courtesy Juerg Diemand

The Biasing Scenario “Biasing” makes low mass halos on top of large overdensities collapse before those on periphery Reionization truncates blue (MP) GC formation Halos that collapse first produce MP GCs of higher metallicity First-collapsing halos produce the MP subpopulation of most luminous galaxies More distant halos survive independently to become dwarf galaxies Strader, Brodie, Cenarro, Beasley & Forbes (2005) Rhode, Zepf & Santos (2005)

Biased Hierarchical Merging Must simultaneously accommodate: (1) MP GC metallicity – galaxy L relation (2) Evidence that most massive galaxies have undergone some degree of merging since z~2 MP GC relation was different at high z Merging was biased – direct result of, and strong end constraint on, hierarchical structure formation MP relation rules out mergers and accretion but only in the local universe for structure forming at present day MP GCs forming at very high z “knew” the galaxy to which they would ultimately belong

Reionization Moore et al (2005) Diemand et al (2005) If blue GC formation is truncated by reionization GC surface density distributions  epoch & (in)homgeneity of reionization Blue GC surface density distributions for galaxies of different masses and environments Bassino et al (2006) NGC 1399 blue GCs surface density fit with an NFW profile, rs=35 kpc  2  Milky Way Fornax Plots courtesy Juerg Diemand

GCs in Fornax Bias of blue GC relative to DM is smaller in Fornax than MW, but still substantial Blue GCs in NGC 1399, LOS =290 km/s (Richtler et al 04), galaxies 380 km/s  small out to 50 kpc, increasingly important further out Combo of GCs and galaxy kinematics can improve M(r) for Fornax Bassino et al profile= Plots courtesy Juerg Diemand

Blue Tilt M87 Metallicity–mass relation for blue GCs Self enrichment? Blue GCs formed with DM halos? Found in NGC 4649 and M87, but not in NGC 4472: Strader et al (2006) and in several BCGs: Harris et al (2006) Some very luminous (z>20) GCs larger – connection to UCDs? Unequal color spreads red GCs ~0.7 blue GCs ~0.4 Color-metallicity relation is non-linear Peng et al (2006)  metallicity spread is larger for MP GCs M87

Sombrero and Spirals Blue tilt seen clearly in extremely deep ACS imaging of Sombrero – 95% detection (Spitler et al 2006 – talk later today) as well as several spirals of later type (Forde et al 2006 – see poster) but NOT in MW

VCC 1087 Beasley et al (2006)  Virgo dE, MV~ –18  12 GC spectra taken with Keck/LRIS  SN ~ 6  GCs are old  Bimodal metallicity distribution  Peaks similar to bright Es  Galaxy has solar metallicity, age ~5 Gyr

dE Formation from Harassment  GC rotation 100±35 km/s, v/ ~ 3.6 most rotationally supported GC system known  disk  M/L vs r, of stars and GCs consistent with purely baryonic mass distribution  SN, GC rotation, galaxy L, consistent with “harassed” Sc spiral falling into Virgo cluster ~5 Gyr ago

GC–Field Star Connection MP GCs appear to have formed with significantly higher (factor >5–10) specific frequencies than MR GCs Degree to which this varies from galaxy to galaxy is unknown (e.g. NGC 5128 & M31 vs MW) Consistent with idea that GCs formed early in star forming episodes (Harris & Harris 2002) In the truncation (reionization?) scenario, star formation was cut off after significant blue GC formation but before much star formation

Mass limits on DM halos Faint end of galaxy LF uniquely accessible in LG Lowest luminosity LG galaxies with confirmed GCs Fornax (MV=–13.1), Sgr (MV=–13.9) Total M ~ 108MSUN Lower mass Galactic dwarfs, e.g., Leo I (MV~–12) do not have GCs M31 And I (MV~–12, mass few x 107) has one GC? Suggests MP GCs formed in halos with a minimum mass of ~107–108 MSUN Caveats: - Only low density group environments explored - Stripping of DM –> present day dwarfs were more massive originally - Differences in baryonic mass-loss for given halo mass Connection to DM halo masses at earliest epochs?

Summary GCs are the one of the best observable links between baryons and dark matter Constrain the epoch and modes of galaxy assembly The GC systems of early and late type galaxies are quite similar  universal formation histories Star formation in early type galaxies was largely completed by z=2, or earlier Red GCs trace the build up of bulges and possibly disks Blue GCs may trace DM halos at earliest times and the epoch and (in)homegeneity of reionization

Lots More! Annual Reviews of Astronomy and Astrophysics Vol. 44 “Extragalactic Globular Clusters and Galaxy formation” by Brodie and Strader (2006) astrop-ph # 0602601