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

Hine, N.K.; Geach, J.E.; Alexander, D.M.; Lehmer, B.D.; Chapman, S.C.; Matsuda, Y.

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


N.K. Hine

J.E. Geach

B.D. Lehmer

S.C. Chapman

Y. Matsuda


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.

Journal Article Type Article
Acceptance Date Oct 20, 2015
Online Publication Date Nov 23, 2015
Publication Date Jan 21, 2016
Deposit Date May 31, 2016
Publicly Available Date Jun 15, 2016
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 455
Issue 3
Pages 2363-2370
Public URL
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Published Journal Article (837 Kb)

Copyright 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.

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