Stellar Populations in Galaxies as traced by Globular

Stellar Populations in Galaxies as traced by Globular Clusters Markus Kissler-Patig

Stellar populations in galaxies Star formation history of galaxies

Why use extragalactic globular clusters? s Star formation = Star cluster formation (not perfect one to one relation but almost) s Easy detection of sub-populations s Easy interpretation of SSPs (as opposed to luminosity weighted properties of the diffuse light) s Discovery of SF events that formed more clusters than stars s Star clusters are proven to be among the oldest objects in the universe - study of the very first SF epochs

THE Key Discovery from Globular Clusters s Distinct sub-populations in early-type galaxies multiple, distinct major star formation episodes To explain: • The presence of an old, metal-poor population in all galaxies • The diversity of the metal-rich population (Puzia, Kissler-Patig, Brodie, Huchra 1999) (Zepf & Ashman 1993 Geisler et al. 1993)

Old, metal-poor globular clusters s They trace a stellar population not detected in the diffuse light (Maraston & Thomas 2000, Lotz et al. 2000) (Harris, Poole 1999) s They are not predicted by SAMs (Beasley et al. 2002)

Old, metal-poor globular clusters s Properties: (Kissler-Patig 2002) s Spatial distribution: Halo (spherical, extended) s Abundances: metal-poor (mean metallicity correlates only weakly, if at all, with galaxy property) s Abundance ratio: high /Fe (short timescales) s Masses: universal distribution (nature or nuture? ) s Sizes: larger than the metal-rich clusters (nature or nurture? ) s High SN: formed with few associated stars

Old, metal-poor globular clusters s Interpretation: (Burgarella, Kissler-Patig, Buat 2000, Kissler-Patig 2002) s Formed in small fragments (dwarf galaxy analogy) s Formed very early on (ages, metallicity, universal) z=10 z=5 z=3 z=1 z=0. 5 z=0 very early 10% 20% half 3/4 today (Courtesy Felix Stoehr)

Old, metal-poor globular clusters s Direct observations of their formation? s Star cluster of 106 M�, 20 Myr … 1 -5 n. Jy at z=6 -10 Just within reach of JWST… (Burgarella & Chapelon 1998) s If star cluster complexes are common - easier 106 M�at z=5. 6 (Ellis, Santos, Kneib, Kuijken 2001) Cluster Complexes at low z in violent environments (Bastian, Emsellem, Kissler-Patig, Maraston 2005)

Metal-rich globular clusters s Not one homogeneous population, but clearly mixed (old + intermediate ages, large range of metallicities) s Includes everything that happened since z~5(3? ) s Formation of the bulges, spheroids s Minor and major dissipative mergers (SF) s Minor and major accretion events (dissipationless) s The challenge: make sense of it…

Metal-rich globular clusters s Caveats in the interpretation: /Fe, HB morphologies (Thomas, Maraston, Korn 2004) (Maraston et al. 2003)

Metal-rich globular clusters Recent results from UV-optical-NIR imaging: Intermediate age, metal-rich populations exist in some galaxies (Hempel, Kissler-Patig et al. 2002, 2003, 2004)

Metal-rich globular clusters Recent results from spectroscopy: Intermediate age, metal-rich populations exist in some galaxies (Puzia, Kissler-Patig, Thomas, Maraston, Saglia, Bender et al. 2004, 2005)