Mergers Interactions and Globular Clusters Duncan Forbes Swinburne

Mergers, Interactions and Globular Clusters Duncan Forbes Swinburne University

Collaborators • • Jean Brodie (UCSC) Robert Proctor (Swinburne) Jay Strader (Harvard) Soeren Larsen (Utrecht) Lee Spitler (Swinburne) Mike Beasley (IAC) Trevor Mendel (Swinburne) Aaron Romanowsky (UCSC)

Bimodality Most (perhaps all) large galaxies reveal two distinct sub-populations of globular clusters. [Fe/H] V-I = -1. 5 0. 95 -0. 5 1. 15

Globular Cluster Formation When ? How ? Ongoing accretion Recent mergers Early formation

Forbes etal 2003

Ongoing GC Accretion Sgr Dwarf Galaxy Whiting-1 M 54 (dwarf nucleus) + 5 GCs + Whiting 1 Well fit by a closed box model Pal 12, Ter 7 [α/Fe] ~ 0 M 54 [α/Fe] ~ +0. 3 (Pritzl et al. 2005) Forbes et al. 2004 .

Canis Major 4 -6 GCs + 2 old open clusters (not BH 176, Pal 1) Is NGC 2808 the nucleus ? Forbes et al. 2004

Recent Mergers Ashman & Zepf 1992: To form an Elliptical galaxy GC system, new metal-rich GCs (red after ~2 Gyrs) form with high efficiency. The total number of metalpoor (blue) GCs is unchanged.

Wet…or Damp Mergers ? Red V-I g-z Forbes etal 2007

Proto-GCs ? Goudfrooij etal 2007

Blue GCs vs galaxy mass major merger

NGC 821 GCs Proctor, Forbes etal 2006

Young Elliptical NGC 1052 AMR Galaxy age Pierce, Brodie, Forbes etal 2005

Redshift 0 1 2 5 Virgo g. E NGC 4365 with KDC Galaxy age Brodie etal 2005

NGC 4649 Galaxy Forbes etal 2005

GC-galaxy properties Similar slope to star-galaxy relation. Provides constraints on hierarchical merging. Brodie & Strader 2006

Early GC Formation Forbes, Brodie & Grillmair (1997) and Beasley, Baugh, Forbes et al. (2002) Require some mechanism for truncating blue GC formation at high z (>5)? Reionisation?

CDM… N-body simulations suggest dark matter halos are “sitting” on top of large overdensities that collapse first (z>10) The majority of these halos combine to form massive galaxies at z=0

Blue GCs vs galaxy mass

Conclusions • Ongoing accretions (minor mergers) make a small contribution to the GC systems of large galaxies. • Although proto-GCs can form in recent major mergers, they make only a very small contribution to the GC systems of today’s ellipticals. • For massive ellipticals the vast bulk of GCs formed early (z > 2, age > 10 Gyrs). • GC scaling relations constrain the hierarchical growth of galaxies.