The nature of extremely red H - [4.5] > 4 galaxies revealed with SEDS and candels

K. I. Caputi, J. S. Dunlop, R. J. McLure, J. S. Huang, G. G. Fazio, M. L.N. Ashby, M. Castellano, A. Fontana, M. Cirasuolo, O. Almaini, E. F. Bell, M. Dickinson, J. L. Donley, S. M. Faber, H. C. Ferguson, M. Giavalisco, N. A. Grogin, D. D. Kocevski, A. M. Koekemoer, D. C. KooK. Lai, J. A. Newman, R. S. Somerville

Research output: Contribution to journalArticlepeer-review

36 Scopus citations


We have analyzed a sample of 25 extremely red H - [4.5] > 4 galaxies, selected using 4.5 μm data from the Spitzer SEDS survey and deep H-band data from the Hubble Space Telescope CANDELS survey, over 180 arcmin2 of the UKIDSS Ultra-Deep Survey field. Our aim is to investigate the nature of this rare population of mid-infrared (mid-IR) sources that display such extreme near-to-mid-IR colors. Using up to 17-band photometry (U through 8.0 μm), we have studied in detail their spectral energy distributions, including possible degeneracies in the photometric redshift/internal extinction (z phot-AV ) plane. Our sample appears to include sources of very different nature. Between 45% and 75% of them are dust-obscured, massive galaxies at 3 < z phot < 5. All of the 24 μm detected sources in our sample are in this category. Two of these have , which at 3 < z phot < 5 suggests that they probably host a dust-obscured active galactic nucleus. Our sample also contains four highly obscured (AV > 5) sources at z phot < 1. Finally, we analyze in detail two z phot 6 galaxy candidates, and discuss their plausibility and implications. Overall, our red galaxy sample contains the tip of the iceberg of a larger population of z > 3 galaxies to be discovered with the future James Webb Space Telescope.

Original languageEnglish (US)
Article numberL20
JournalAstrophysical Journal Letters
Issue number1
StatePublished - May 1 2012

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • galaxies: evolution
  • galaxies: high-redshift
  • infrared: galaxies

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