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Published March 10, 2012 | Published
Journal Article Open

Major-merger Galaxy Pairs in the COSMOS Field — Mass-dependent Merger Rate Evolution since z = 1


We present results of a statistical study of the cosmic evolution of the mass-dependent major-merger rate since z = 1. A stellar mass limited sample of close major-merger pairs (the CPAIR sample) was selected from the archive of the COSMOS survey. Pair fractions at different redshifts derived using the CPAIR sample and a local K-band-selected pair sample show no significant variations with stellar mass. The pair fraction exhibits moderately strong cosmic evolution, with the best-fitting function of f_(pair) = 10^(–1.88(± 0.03))(1 + z)^(2.2(± 0.2)). The best-fitting function for the merger rate is R_(mg) (Gyr^(–1)) = 0.053 × (M_(star)/10^(10.7) M_☉ )^(0.3)(1 + z)^(2.2)/(1 + z/8). This rate implies that galaxies of M_(star) ~ 10^(10)-10^(11.5) M_☉ have undergone ~0.5-1.5 major mergers since z = 1. Our results show that, for massive galaxies (M_(star) ≥ 10^(10.5) M_☉) at z ≤ 1, major mergers involving star-forming galaxies (i.e., wet and mixed mergers) can account for the formation of both ellipticals and red quiescent galaxies (RQGs). On the other hand, major mergers cannot be responsible for the formation of most low mass ellipticals and RQGs of M_(star) ≾ 10^(10.3) M_☉. Our quantitative estimates indicate that major mergers have significant impact on the stellar mass assembly of the most massive galaxies (M_(star) ≥ 10^(11.3) M_☉), but for less massive galaxies the stellar mass assembly is dominated by the star formation. Comparison with the mass-dependent (ultra)luminous infrared galaxies ((U)LIRG) rates suggests that the frequency of major-merger events is comparable to or higher than that of (U)LIRGs.

Additional Information

© 2012 American Astronomical Society. Received 2011 September 7; accepted 2011 November 22; published 2012 February 16. This work is based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555; and the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407; also based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; the XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA; the European Southern Observatory under Large Program 175.A-0839, Chile; Kitt Peak National Observatory, Cerro Tololo Inter-American Observatory, and the National Optical Astronomy Observatory, which are operated by the Association of Universities for Research in Astronomy (AURA), Inc., under cooperative agreement with the National Science Foundation; the National Radio Astronomy Observatory which is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.; and the Canada–France–Hawaii Telescope with MegaPrime/MegaCam operated as a joint project by the CFHT Corporation, CEA/DAPNIA, the NRC and CADC of Canada, the CNRS of France, TERAPIX and the University of Hawaii. C.K.X. acknowledges Kevin Bundy for constructive discussions and Alexie Leauthaud for help in analyzing the COSMOS HST-ACS lensing catalog. Zara Scoville is thanked for proofing the English of the manuscript. Y.Z. and Y.G. are grateful for the financial support from the NSF of China (grant Nos. 10833006 and 10903029). Y.Z. thanks IPAC for the hospitality and the financial support during his visit.

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