2012ApJ...744..155W

In order to find the most extreme dust-hidden high-redshift galaxies, we select 196 extremely red objects in the K_S and Infrared Array Camera (IRAC) bands (KIEROs, [K_s- 4.5 µm]_AB> 1.6) in the 0.06 deg² Great Observatories Origins Deep Surveys-North (GOODS-N) region. This selection avoids the Balmer breaks of galactic spectra at z < 4 and picks up red galaxies with strong dust extinction. The photometric redshifts of KIEROs are between 1.5 and 5, with ∼70% at z ∼ 2-4. KIEROs are very massive, with M_{sstarf} ∼ 10¹⁰-10¹² M_☉. They are optically faint and usually cannot be picked out by the Lyman break selection. On the other hand, the KIERO selection includes approximately half of the known millimeter and submillimeter galaxies in the GOODS-N. Stacking analyses in the radio, millimeter, and submillimeter all show that KIEROs are much more luminous than average 4.5 µm-selected galaxies. Interestingly, the stacked fluxes for Advanced Camera for Surveys (ACS)-undetected KIEROs in these wave bands are 2.5-5 times larger than those for ACS-detected KIEROs. With the stacked radio fluxes and the local radio-FIR correlation, we derive mean infrared luminosities of (2-7) x10¹² L_☉ and mean star formation rates (SFRs) of 400-1200 M _☉/yr for KIEROs with redshifts. We do not find evidence of a significant subpopulation of passive KIEROs. The large stellar masses and SFRs imply that KIEROs are z > 2 massive galaxies in rapid formation. Our results show that a large sample of dusty ultraluminous sources can be selected in this way and that a large fraction of high-redshift star formation is hidden by dust.