It is not easy being green: the evolution of galaxy colour in the EAGLE simulation

James W. Trayford*, Tom Theuns, Richard G. Bower, Robert A. Crain, Claudia del P. Lagos, Matthieu Schaller, Joop Schaye

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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We examine the evolution of intrinsic u-r colours of galaxies in the EAGLE cosmological hydrodynamical simulations, which has been shown to reproduce the observed redshift z = 0.1 colour-magnitude distribution well, with a focus on z < 2. The median u-r of star-forming ('blue cloud') galaxies reddens by 1 mag from z = 2 to 0 at fixed stellar mass, as their specific star formation rates decrease with time. A red sequence starts to build-up around z = 1, due to the quenching of low-mass satellite galaxies at the faint end, and due to the quenching of more massive central galaxies by their active galactic nuclei (AGN) at the bright end. This leaves a dearth of intermediate-mass red sequence galaxies at z = 1, which is mostly filled in by z = 0. We quantify the time-scales of colour transition finding that most galaxies spend less than 2 Gyr in the 'green valley'. We find the time-scale of transition to be independent of quenching mechanism, i.e. whether a galaxy is a satellite or hosting an AGN. On examining the trajectories of galaxies in a colour-stellar mass diagram, we identify three characteristic tracks that galaxies follow (quiescently star-forming, quenching and rejuvenating galaxies) and quantify the fraction of galaxies that follow each track.

Original languageEnglish
Pages (from-to)3925-3939
Number of pages15
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date23 May 2016
Publication statusPublished - 21 Aug 2016


  • galaxies: evolution
  • galaxies: formation
  • UJRI
  • STFC
  • ST/F001166/1
  • ST/K00042X/1
  • ST/H008519/1


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