University of Hertfordshire

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From the same journal

By the same authors

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

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  • stv2448

    Final published version, 1.13 MB, PDF document

  • N.~K. Hine
  • J.~E. Geach
  • D.~M. Alexander
  • B.~D. Lehmer
  • S.~C. Chapman
  • Y. Matsuda
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Original languageEnglish
Pages (from-to)2363-2370
Number of pages8
JournalMonthly Notices of the Royal Astronomical Society
Early online date21 Nov 2015
Publication statusPublished - 21 Jan 2016


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.


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, the version of record is available on line at doi: 10.1093/mnras/stv2448

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