The Nature of Extremely Red H - [4.5] > 4 Galaxies Revealed with SEDS and CANDELS
Dickinson, M.; Ferguson, H. C.; Giavalisco, M.; McLure, R. J.; Dunlop, J. S.; Castellano, M.; Koekemoer, A. M.; Fazio, G. G.; Huang, J. -S.; Fontana, A.; Faber, S. M.; Cirasuolo, M.; Ashby, M. L. N.; Bell, E. F.; Koo, D. C.; Grogin, N. A.; Caputi, K. I.; Kocevski, D. D.; Donley, J. L.; Almaini, O.; Newman, J. A.; Lai, K.; Somerville, R. S.
United Kingdom, Netherlands, United States, Italy
Abstract
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 S(24 \, \mu m)>300 \, \mu Jy, 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.