LoCuSS: pre-processing in galaxy groups falling into massive galaxy clusters at z = 0.2

Research output: Contribution to journalLetterpeer-review


Colleges, School and Institutes

External organisations

  • INAF - Osservatorio Astronomico di Brera, via Brera 28, I-20122 Milano, Italy
  • University of Helsinki
  • Max Planck Institut fur extraterrestrische Physik, Giessenbachstraße, D-85748 Garching, Germany
  • Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA


We report direct evidence of pre-processing of the galaxies residing in galaxy groups falling into galaxy clusters drawn from the Local Cluster Substructure Survey (LoCuSS). 34 groups have been identified via their X-ray emission in the infall regions of 23 massive (〈M200〉 = 1015 M) clusters at 0.15 < z < 0.3. Highly complete spectroscopic coverage combined with 24 μm imaging from Spitzer allows us to make a consistent and robust selection of cluster and group members including star-forming galaxies down to a stellar mass limit of M = 2 × 1010 M. The fraction fSF of star-forming galaxies in infalling groups is lower and with a flatter trend with respect to clustercentric radius when compared to the rest of the cluster galaxy population. At R ≈ 1.3 r200, the fraction of star-forming galaxies in infalling groups is half that in the cluster galaxy population. This is direct evidence that star-formation quenching is effective in galaxies already prior to them settling in the cluster potential, and that groups are favourable locations for this process.


Original languageEnglish
Pages (from-to)L79–L83
Number of pages5
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Early online date12 Oct 2017
Publication statusPublished - 1 Jan 2018


  • galaxies: clusters: general, galaxies: evolution, galaxies: groups: general, galaxies: star formation