Abstract
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 language | English |
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Article number | 84 |
Journal | Astrophysical Journal |
Volume | 816 |
Issue number | 2 |
DOIs | |
Publication status | Published - 14 Jan 2016 |
Keywords / Materials (for Non-textual outputs)
- galaxies: evolution
- galaxies: formation
- galaxies: high-redshift
- galaxies: structure