The colour distribution of galaxies at redshift five

A. B. Rogers, R. J. McLure, J. S. Dunlop, R. A.A. Bowler, E. F. Curtis-Lake, P. Dayal, S. M. Faber, H. C. Ferguson, S. L. Finkelstein, N. A. Grogin, N. P. Hathi, D. Kocevski, A. M. Koekemoer, P. Kurczynski

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52 Scopus citations


We present the results of a study investigating the rest-frame ultraviolet (UV) spectral slopes of redshift z ≈ 5 Lyman-break galaxies (LBGs). By combining deep Hubble Space Telescope imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey and Hubble Ultra-Deep Field with ground-based imaging from the UKIRT Infrared Deep Sky Survey Ultra Deep Survey, we have produced a large sample of z≈5 LBGs spanning an unprecedented factor of >100 in UV luminosity. Based on this sample we find a clear colour-magnitude relation (CMR) at z≈5, such that the rest-frame UV slopes (β) of brighter galaxies are notably redder than their fainter counterparts. We determine that the z≈5 CMR is well described by a linear relationship of the form: dβ = (-0.12 ± 0.02)dMUV, with no clear evidence for a change in CMR slope at faint magnitudes (i.e. MUV ± -18.9). Using the results of detailed simulations we are able, for the first time, to infer the intrinsic (i.e. free from noise) variation of galaxy colours around the CMR at z≈5. We find significant (12α) evidence for intrinsic colour variation in the sample as a whole. Our results also demonstrate that the width of the intrinsic UV slope distribution of z≈5 galaxies increases from Δ β≃ 0.1 at MUV = -18 to Δ β ≃0.4 at MUV = -21. We suggest that the increasing width of the intrinsic galaxy colour distribution and the CMR itself are both plausibly explained by a luminosity-independent lower limit of β ≈ -2.1, combined with an increase in the fraction of red galaxies in brighter UV-luminosity bins.

Original languageEnglish (US)
Pages (from-to)3714-3725
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Jun 2014

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: high-redshift
  • Galaxies: starburst
  • Galaxies: stellar content
  • Ultraviolet: galaxies


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