M.Kissler-Patig, ESOM.Kissler-Patig, ESO

The chemistry of (not that) simple stellar

populations: extragalactic globular

clustersM.Kissler-Patig (ESO)

Collaborators:T.Puzia (his PhD), D.Thomas, C.Maraston,

R.Saglia, R.Bender, P.Goudfrooij, T.Richtler, M.Hempel

M.Kissler-Patig, ESO

Extragalactic Globular Clusters

M.Kissler-Patig, ESO

Globular clusters or integrated light?

Integrated light:+ tracer of most mass+ bright (easily observed]- studied at small radii- composite stellar pop, luminosity weighted =

complicated to understandGlobular clusters:

+ simple stellar pops (easier age determination]+ studied at large radii (2-3 Reff], also traces

halo pop- only 1% of total mass - link to SF less trivial

M.Kissler-Patig, ESO

Our project (FORS+ISAAC/VLT]

Photometry + Spectroscopy: (Puzia et al. A&A in press) SPECTRO PHOTOMERY (FORS2/ISAAC)

3500-6000A [5A]B, V, R, I, K (in seconds)

NGC 1380 7h ......, 700, ......, 700, ...... NGC 2434 7h ......, 700, ......, 700, ......

NGC 3115 3h 160, 300, 160, 300, 15500

NGC 3379 4.3h ......, 300, ......, 300, ......

NGC 3585 7.5h 800, ......, ......, 800, ......

NGC 5846 9h 900, 300, 160, 300, 10000

NGC 7192 8.75h 900, 600, 900, 600, 12000

M.Kissler-Patig, ESO

Hitting globular clusters

Controlling the sample:Target selection in– Color-color diagrams– Color-magnitude

diagramsHit-rates of >90% in

confidence regions

M.Kissler-Patig, ESO

Measuring Lick indices

IncreasingMgb strength

M.Kissler-Patig, ESO

Results: two different populationsMetal-poor clusters:

– homogeneous halo pop.

– old ages >10 Gyr– no/little age spread

(Kissler-Patig 2002, Ap&SS. 281, 487]

Metal-rich clusters:– large spread in age– younger mean age– small HB effects

possibleSSP models from Maraston et al 2002

(see also Poster by Maren Hempel)

M.Kissler-Patig, ESO

Results: element ratiosMetal-poor clusters:

– large spread in /Fe, but narrow dynamic range

Metal-rich clusters:– “young” clusters have

close to solar /Fe– “old” clusters have high

/Fe ratio, similar to the diffuse light of their hosts

SSP models from Thomas et al 2002

M.Kissler-Patig, ESO

Summary from spectroscopy

• Metal-poor globular clusters are homogeneous in age and old -- their -elt are uncertain

• Metal-rich globular clusters show a large spread in age

• Old metal-rich globular clusters have high -elt abundances, similar to the integrated light of their (giant elliptical) hosts

• Young metal-rich globular clusters have lower -elt abundances

M.Kissler-Patig, ESO

Conclusions

• Globular clusters are the best tracers for star-formation epochs in early-type galaxies

• Many early-type galaxies show recent star formation

• Quantifying the amount of recent star formation is still uncertain (but we are working on it…)

• The oldest star-formation events produced higher -elt ratio that recent ones