Infrared Color Selection of Massive Galaxies at z > 3

T. Wang, D. Elbaz, C. Schreiber, M. Pannella, X. Shu, S. P. Willner, M. L. N. Ashby, J.-S. Huang, A. Fontana, A. Dekel, E. Daddi, H. C. Ferguson, J. Dunlop, L. Ciesla, A. M. Koekemoer, M. Giavalisco, K. Boutsia, S. Finkelstein, S. Juneau, G. BarroD. C. Koo, M. J. Michałowski, G. Orellana, Y. Lu, M. Castellano, N. Bourne, F. Buitrago, P. Santini, S. M. Faber, N. Hathi, R. A. Lucas, P. G. Pérez-González

Research output: Contribution to journalArticlepeer-review


We introduce a new color selection technique to identify high-redshift, massive galaxies that are systematically missed by Lyman-break selection. The new selection is based on the H160 (H) and Infrared Array Camera (IRAC) 4.5 μm bands, specifically H-[4.5]\gt 2.25 mag. These galaxies, called “HIEROs,” include two major populations that can be separated with an additional J - H color. The populations are massive and dusty star-forming galaxies at z\gt 3 ({JH}-{blue}) and extremely dusty galaxies at z≲ 3 ({JH}-{red}). The 350 arcmin2 of the GOODS-North and GOODS-South fields with the deepest Hubble Space Telescope (HST)/Wide Field Camera 3 (WFC3) near-infrared and IRAC data contain as many as 285 HIEROs down to [4.5]\lt 24 mag. Inclusion of the most extreme HIEROs, not even detected in the H band, makes this selection particularly complete for the identification of massive high-redshift galaxies. We focus here primarily on {JH}-{blue} (z\gt 3) HIEROs, which have a median photometric redshift <z> ˜ 4.4 and stellar mass {M}*˜ {10}10.6 {M}⊙ and are much fainter in the rest-frame UV than similarly massive Lyman-break galaxies (LBGs). Their star formation rates (SFRs), derived from their stacked infrared spectral energy distributions (SEDs), reach ˜240 {M}⊙ yr-1, leading to a specific SFR, {{sSFR}}\equiv {{SFR}}/{M}*˜ 4.2 Gyr-1, suggesting that the sSFRs for massive galaxies continue to grow at z\gt 2 but at a lower growth rate than from z = 0 to z = 2. With a median half-light radius of 2 kpc, including ˜ 20% as compact as quiescent (QS) galaxies at similar redshifts, {JH}-{blue} HIEROs represent perfect star-forming progenitors of the most massive ({M}*≳ {10}11.2 {M}⊙ ) compact QS galaxies at z˜ 3 and have the right number density. HIEROs make up ˜ 60% of all galaxies with {M}*\gt {10}10.5 {M}⊙ identified at z\gt 3 from their photometric redshifts. This is five times more than LBGs with nearly no overlap between the two populations. While HIEROs make up 15%-25% of the total SFR density at z˜ 4-5, they completely dominate the SFR density taking place in {M}*\gt {10}10.5 {M}⊙ galaxies, and HIEROs are therefore crucial to understanding the very early phase of massive galaxy formation.
Original languageEnglish
Article number84
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 14 Jan 2016


  • galaxies: evolution
  • galaxies: formation
  • galaxies: high-redshift
  • galaxies: structure


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