Observational constraints on the merger history of galaxies since z ≈ 6: probabilistic galaxy pair counts in the CANDELS fields



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Duncan, Kenneth and Conselice, Christopher J. and Mundy, Carl and Bell, Eric and Donley, Jennifer and Galametz, Audrey and Guo, Yicheng and Grogin, Norman A. and Hathi, Nimish and Kartaltepe, Jeyhan and Kocevski, Dale and Koekemoer, Anton M. and Pérez González, Pablo Guillermo and Mantha, Kameswara B. and Snyder, Gregory F. and Stefanon, Mauro (2019) Observational constraints on the merger history of galaxies since z ≈ 6: probabilistic galaxy pair counts in the CANDELS fields. Astrophysical journal, 876 (2). ISSN 0004-637X

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Official URL: http://dx.doi.org/10.3847/1538-4357/ab148a


Galaxy mergers are expected to have a significant role in the mass assembly of galaxies in the early universe, but there are very few observational constraints on the merger history of galaxies at z > 2. We present the first study of galaxy major mergers (mass ratios <1:4) in mass-selected samples out to z ≈ 6. Using all five fields of the Hubble Space Telescope / CANDELS survey and an probabilistic pais-count methodology that incorporates the full photometric redshift posteriors and corrections for stellar masss completeness, we measure galaxy pair-counts for prohected separations between 5 and 30 kpc in stellar mass selected samples at 9.7 < log_(10)(M*/Mꙩ) < 10.3 and log_(10)(M*/Mꙩ) < 10.3. We find that the major merger pair fraction rises with redshift to z ≈ 6 proportional to (1 + z)^(m), with m = 0.8 ± 0.2 (m = 1.8 ± 0.2) for log_(10)(M */Mꙩ) < 10.3 (9.7 < log_(10)(M */Mꙩ) < 10.3). Investigating the pair fraction as a function of mass ratio between 1:20 and 1:1, we find no evidence for a strong evolution in the relative numbers of minor to major mergers out to z < 3. Using evolving merger timescales, we find that the merger rate per galaxy (R) rises rapidly from 0.07 ± 0.01 Gyr^(−1) at z < 1 to 7.6 ± 2.7 Gyr^(−1) at z = 6 for galaxies at log_(10)(M*/Mꙩ) < 10.3. The corresponding comoving major merger rate density remains roughly constant during this time, with rates of Γ ≈ 10^(−4) Gyr^(−1) Mpc^(−3) . Based on the observed merger rates per galaxy, we infer specific mass accretion rates from major mergers that are comparable to the specific star formation rates for the same mass galaxies at z > 3 - observational evidence that mergers are as important a mechanism for building up mass at high redshift as in situ star formation.

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© 2019. The American Astronomical Society. The research leading to these results has received funding from the European Union Seventh Framework Programme FP7/2007-2013/ under grant agreement number 607254. This publication reflects only the authors’ view and the European Union is not responsible for any use that may be made of the information contained therein. K.J.D. acknowledges support from the ERC Advanced Investigator programme NewClusters 321271. We would also like to acknowledge funding from the Science and Technology Facilities Council (STFC) and the Leverhulme Trust. P.G.P.-G. wishes to acknowledge support from Spanish Government MINECO Grant AYA2015-63650- P. K.B.M. acknowledges support from the HST archival research grant HST-AR-15040. This work is based on observations taken by the CANDELS Multi-Cycle Treasury Program with the NASA/ESA HST, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. The VUDS spectroscopic data is in this work is based on data obtained with the European Southern Observatory Very Large Telescope, Paranal, Chile, under Large Program 185.A-0791, and made available by the VUDS team at the CESAM data center, Laboratoire d’Astrophysique de Marseille, France.

Uncontrolled Keywords:Catalogs source identification; Stellar mass functions; Photometric redshifts; Star-formation; Distant galaxies; Time-scales; Illustris project; Major mergers; Deep survey; Evolution
Subjects:Sciences > Physics > Astrophysics
ID Code:57080
Deposited On:08 Oct 2019 08:53
Last Modified:08 Oct 2019 09:35

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