Galaxies 09: Assembly, Gas Content and Star Formation History of Galaxies

Shardha Jogee
University of Texas at Austin

Galaxy Mergers and their Impact on Star Formation over the last 10 Gyr

T. Weinzirl (University of Texas at Austin)
S. Miller (University of Oxford)
K. Penner (University of Arizona, Steward Observatory)
R. E. Skelton (Max-Planck-Institut f\"{u}r Astronomie)
C. J. Conselice (The University of Nottingham))
R. S. Somerville (Max-Planck-Institut f\"{u}r Astronomie)
E. F. Bell (Max-Planck-Institut f\"{u}r Astronomie)
X. Z. Zheng (Purple Mountain Observatory)
H-W. Rix (Max-Planck-Institut f\"{u}r Astronomie))
A. R. Robaina (Max-Planck-Institut f\"{u}r Astronomie) )
F. D. Barazza (Laboratoire d'Astrophysique, \'Ecole Polytechnique F\'ed\'erale de Lausanne)
M. Barden (Institute for Astro- and Particle Physics, University of Innsbruck)
A. Borch (Max-Planck-Institut f\"{u}r Astronomie)
S. V. Beckwith (Johns Hopkins University)
J. A. Caldwell (University of Texas, McDonald Observatory)
C. Y. Peng (NRC Herzberg Institute of Astrophysics)
C. Heymans (SUPA, Institute for Astronomy, University of Edinburgh)
D. H. McIntosh (University of Massachusetts)
B. H{\"a}u{\ss}ler (The University of Nottingham)
K. Jahnke (Max-Planck-Institut f\"{u}r Astronomie)
K. Meisenheimer (Max-Planck-Institut f\"{u}r Astronomie)
S. F. Sanchez (Centro Astronómico Hispano Alemán)
L. Wisotzki (Astrophysikalisches Institut Potsdam)
C. Wolf (University of Oxford)
C. Papovich (Texas A\&M University)

Mergers, smooth accretion, and secular processes are relevant for the assembly and central activity of galaxies in hierarchical models of galaxy evolution, but their relative importance at different epochs remains hotly debated. I will discuss evidence that major mergers play a less important role in driving galaxy evolution since z~2 than previously thought, based on two of our published studies: Jogee et al. & the GEMS collaboration 2009 (J09) and Weinzirl et al. (2009; W09). In W09, constraints on the merger history over the last 10 Gyr are presented based on the structural property of local bulges.In J09, we explore the frequency of galaxy mergers and their impact on star formation over the last 7 Gyr using HST ACS,COMBO-17, and Spitzer data from the GEMS survey. We also compare the empirical merger history for high mass galaxies to theoretical predictions from $\Lambda$CDM-based halo occupation distribution models, semi-analytic models, and hydrodynamic SPH simulations. Among high mass systems, we find that the mean SFR of visibly merging systems is only modestly enhanced compared to non-interacting galaxies, such that visibly merging systems only account for less than 30\% of the cosmic SFR density over this interval. Thus, the decline in the cosmic SFR density over the last 7 Gyr is predominantly shaped by non-interacting galaxies. Future facilities like ALMA will be instrumental in exploring this issue further.

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