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An enhanced merger fraction within the galaxy population of the SSA22 protocluster at z = 3.1.

Hine, N.K. and Geach, J.E. and Alexander, D.M. and Lehmer, B.D. and Chapman, S.C. and Matsuda, Y. (2016) 'An enhanced merger fraction within the galaxy population of the SSA22 protocluster at z = 3.1.', Monthly notices of the Royal Astronomical Society., 455 (3). pp. 2363-2370.


The overdense environments of protoclusters of galaxies in the early Universe (z > 2) are expected to accelerate the evolution of galaxies, with an increased rate of stellar mass assembly and black hole accretion compared to co-eval galaxies in the average density ‘field’. These galaxies are destined to form the passive population of massive galaxies that dominate the cores of rich clusters today. While signatures of the accelerated growth of galaxies in the SSA22 protocluster (z = 3.1) have been observed, the mechanism driving this remains unclear. Here we show an enhanced rate of galaxy–galaxy mergers could be responsible. We morphologically classify Lyman-break Galaxies (LBGs) in the SSA22 protocluster and compare these to those of galaxies in the field at z = 3.1 as either active mergers or non-merging using Hubble Space Telescope ACS/F814W imaging, probing the rest-frame ultraviolet stellar light. We measure a merger fraction of 48 ± 10 per cent for LBGs in the protocluster compared to 30 ± 6 per cent in the field. Although the excess is marginal, an enhanced rate of mergers in SSA22 hints that galaxy–galaxy mergers are one of the key channels driving accelerated star formation and AGN growth in protocluster environments.

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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:20 October 2015
Date deposited:15 June 2016
Date of first online publication:23 November 2015
Date first made open access:No date available

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