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)  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  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

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

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)  They trace a stellar population not detected in the diffuse light  They are not predicted by SAMs (Beasley et al. 2002) (Harris, Harris, Poole 1999) (Maraston & Thomas 2000, Lotz et al. 2000)

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 S N : formed with few associated stars  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 S N : formed with few associated stars

Old, metal-poor globular clusters z=0z=0.5z=1z=3z=5z=10 (Courtesy Felix Stoehr) 20%10%very earlyhalf3/4today  Interpretation: (Burgarella, Kissler-Patig, Buat 2000, Kissler-Patig 2002)  Formed in small fragments (dwarf galaxy analogy)  Formed very early on (ages, metallicity, universal)  Interpretation: (Burgarella, Kissler-Patig, Buat 2000, Kissler-Patig 2002)  Formed in small fragments (dwarf galaxy analogy)  Formed very early on (ages, metallicity, universal)

Old, metal-poor globular clusters  Direct observations of their formation?  Star cluster of 10 6 M , 20 Myr … 1-5 nJy at z=6-10 Just within reach of JWST… (Burgarella & Chapelon 1998)  If star cluster complexes are common - easier  Direct observations of their formation?  Star cluster of 10 6 M , 20 Myr … 1-5 nJy at z=6-10 Just within reach of JWST… (Burgarella & Chapelon 1998)  If star cluster complexes are common - easier 10 6 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  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…  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…

Metal-rich globular clusters  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)

Conclusions z=0z=0.5z=1z=3z=5z=10 20%10%very earlyhalf3/4today The galaxy formation models need to explain these stellar populations:

z=0z=0.5z=1z=3z=5z=10 20%10%very earlyhalf3/4today z~1 z~0.1