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Stellar Populations in Galaxies as traced by Globular Clusters

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?. Star formation = Star cluster formation (not perfect one to one relation but almost)

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Stellar Populations in Galaxies as traced by Globular Clusters

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

  2. Stellar populations in galaxies Star formation history of galaxies

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

  4. THE Key Discovery from Globular Clusters • 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 1993Geisler et al. 1993)

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

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

  7. Old, metal-poor globular clusters • Interpretation: (Burgarella, Kissler-Patig, Buat 2000, Kissler-Patig 2002) • Formed in small fragments (dwarf galaxy analogy) • 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)

  8. Old, metal-poor globular clusters • Direct observations of their formation? • Star cluster of 106 M, 20 Myr … 1-5 nJy at z=6-10Just within reach of JWST…(Burgarella & Chapelon 1998) • If star cluster complexes are common - easier Cluster Complexes at low z in violent environments (Bastian, Emsellem, Kissler-Patig, Maraston 2005) 106 M at z=5.6 (Ellis, Santos, Kneib, Kuijken 2001)

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

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

  11. 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)

  12. 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)

  13. Conclusions The galaxy formation models need to explain these stellar populations: z=10 z=5 z=3 z=1 z=0.5 z=0 very early 10% 20% half 3/4 today

  14. z=10 z=5 z=3 z=1 z=0.5 z=0 very early 10% 20% half 3/4 today z~0.1 z~1

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