By Soren S. Larsen (arXiv: ) Reporter: Sun Wei

Tools to study (extra)galactic SF histories Long-lived Bright Question: What are the conditions for the formation and survival of massive clusters?

Focusing on… The General problem of cluster formation Dynamical evolution The shape of the initial cluster mass function (ICMF)

Basic observation results-Milky Way Open and Globular Clusters Mass upper-limit of OCs:, a order of magnitude lower than that of GCs – Selection Bias Flat mass spectrum at low masses of GCs: a hint of dynamical evolution McLaughlin & Pudritz 1996 Piskunov et al 2008

Basic Observation Result-Local Group Magellanic Clouds Old age as a defining criterion Similar LF of old LMC clusters to that of Galactic GCs (Harris 1991) – similar MFs Similar power law distributions of the young LMC and MW clusters IC 1613: very few star clusters M 31 & M 33: appear consistent De Grijs & Anders 2006

Basic Observation Result-Beyond the Local Group Most studied: Starburst (M82) & merging (M51) galaxies Age range: More massive ( ) young clusters were found in normal spiral galaxies (Larsen & Richtler 2004: M 83) Later than Sb

Formation of Clusters Giant Molecular Cloud -> Embedded star clusters Star formation efficiency Relation between mass function of GMCs and the clusters forming within them The embedded phase Ablating process of the gas

GMC -> Embedded Clusters SF efficiency Average density of GMC: Density needed for star forming: and : at least 20% - 30% for early dynamical evolution Relation between MF of GMCs and Clusters Upper mass: Power law slope: Williams & McKee 1997

The embedded phase Duration: uncertain but short (e.g., R136, Antennae, NGC4449, etc) Physical mechanism of expelling the gas? (Krumholtz & Matzner 2009) Supernovae? Stellar winds or trapped infrared/Lyα photons? Radiation pressure is most likely the dominant gas- evacuation mechanism in massive clusters.

Dynamical Evolution Early dynamical evolution: ‘Infant Mortality’ Clusters disruption after/with the gas expulsion Age distribution of mass-limited cluster samples in M51 & M33: The cluster-formation efficiency: Γ~8%? Secular evolution Maxwellian velocity distribution External shocks Dissolution timescale Evolution of MF: connection between OC & GC? M 33: Sarajedini & Mancone 2007 M 51: Fall et al. 2005

No Conclusion but