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The Greater Impact of Mergers on the Growth of Massive Galaxies: Implications for Mass Assembly and Evolution since z≃1

Bundy, Kevin and Fukugita, Masataka and Ellis, Richard S. and Targett, Thomas A. and Belli, Sirio and Kodama, Tadayuki (2009) The Greater Impact of Mergers on the Growth of Massive Galaxies: Implications for Mass Assembly and Evolution since z≃1. Astrophysical Journal, 697 (2). pp. 1369-1383. ISSN 0004-637X.

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Using deep infrared observations conducted with the MOIRCS imager on the Subaru Telescope in the northern GOODS field combined with public surveys in GOODS-S, we investigate the dependence on stellar mass, M_*, and galaxy type of the close pair fraction (5 h^(–1) kpc < r_sep < 20 h^(–1) kpc) and implied merger rate. In terms of combined depth and survey area, our publicly available mass-limited sample represents a significant improvement over earlier infrared surveys used for this purpose. In common with some recent studies, we find that the fraction of paired systems that could result in major mergers is low (~4%) and does not increase significantly with redshift to z ≈ 1.2, with α(1 + z)^(1.6±1.6). Our key finding is that massive galaxies with M_*>10^(11) M_☉ are more likely to host merging companions than less massive systems (M_* ~ 10^(10)M_☉). We find evidence for a higher pair fraction for red, spheroidal hosts compared to blue, late-type systems, in line with expectations based on clustering at small scales. The so-called "dry" mergers between early-type galaxies devoid of star formation (SF) represent nearly 50% of close pairs with M_*>3 × 10^(10)M_☉ at z ~ 0.5, but less than 30% at z ~ 1. This result can be explained by the increasing abundance of red, early-type galaxies at these masses. We compare the volumetric merger rate of galaxies with different masses to mass-dependent trends in galaxy evolution. Our results reaffirm the conclusion of Bundy et al. that major mergers do not fully account for the formation of spheroidal galaxies since z ~ 1. In terms of mass assembly, major mergers contribute little to galaxy growth below M_* ~ 3 × 10^(10)M_☉ but play a more significant role among galaxies with M_*≳ 10^(11) M_☉ ~ 30% of which have undergone mostly dry mergers over the observed redshift range. Overall, the relatively rapid and recent coalescence of high-mass galaxies mirrors the expected hierarchical growth of halos and is consistent with recent model predictions, even if the top-down suppression of SF and morphological evolution (i.e., "downsizing") involves additional physical processes.

Item Type:Article
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URLURL TypeDescription
Bundy, Kevin0000-0001-9742-3138
Ellis, Richard S.0000-0001-7782-7071
Belli, Sirio0000-0002-5615-6018
Additional Information:© 2009. The American Astronomical Society. Received 2008 September 10; accepted 2009 March 12; published 2009 May 12. We would like to thank Ichi Tanaka for his help in obtaining our Subaru observations and Yen-Ting Lin and Phil Hopkins for useful discussions. M.F. is supported by a Grant-in-Aid of the Ministry of Education of Japan. R.S.E. acknowledges the financial support of the Royal Society.
Funding AgencyGrant Number
Ministry of Education, Culture, Sports, Science and Technology (MEXT)UNSPECIFIED
Subject Keywords:galaxies: evolution galaxies: formation galaxies: interactions
Issue or Number:2
Record Number:CaltechAUTHORS:20090811-154619793
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Official Citation:The Greater Impact of Mergers on the Growth of Massive Galaxies: Implications for Mass Assembly and Evolution since z≃1 Kevin Bundy, Masataka Fukugita, Richard S. Ellis, Thomas A. Targett, Sirio Belli, and Tadayuki Kodama 2009 ApJ 697 1369-1383 doi: 10.1088/0004-637X/697/2/1369
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14975
Deposited By: Ruth Sustaita
Deposited On:02 Sep 2009 20:03
Last Modified:23 Nov 2019 00:19

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