2016ApJ...816...84W

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]> 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> 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]< 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> 3) HIEROs, which have a median photometric redshift <z>∼4.4 and stellar mass M_*∼10^10.6M_☉ 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≡SFR/M_*∼4.2 Gyr^–1, suggesting that the sSFRs for massive galaxies continue to grow at z> 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_*≳10^11.2M_☉) compact QS galaxies at z∼3 and have the right number density. HIEROs make up ∼60% of all galaxies with M_*> 10^10.5M_☉ identified at z> 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_*> 10^10.5M_☉ galaxies, and HIEROs are therefore crucial to understanding the very early phase of massive galaxy formation.