Abstract
Abstract The largest Herschel extragalactic surveys, H-ATLAS and HerMES, have selected a sample of “ultrared” dusty star-forming galaxies (DSFGs) with rising SPIRE flux densities (S 500 > S 350 > S 250; the so-called “500 μm risers”) as an efficient way for identifying DSFGs at higher redshift (z > 4). In this paper, we present a large Spitzer follow-up program of 300 Herschel ultrared DSFGs. We have obtained high-resolution Atacama Large Millimeter/submillimeter Array, Northern Extended Millimeter Array, and SMA data for 63 of them, which allow us to securely identify the Spitzer/IRAC counterparts and classify them as gravitationally lensed or unlensed. Within the 63 ultrared sources with high-resolution data, ∼65% appear to be unlensed and ∼27% are resolved into multiple components. We focus on analyzing the unlensed sample by directly performing multiwavelength spectral energy distribution modeling to derive their physical properties and compare with the more numerous z ∼ 2 DSFG population. The ultrared sample has a median redshift of 3.3, stellar mass of 3.7 × 1011 M ⊙, star formation rate (SFR) of 730 M ⊙ yr−1, total dust luminosity of 9.0 × 1012 L ⊙, dust mass of 2.8 × 109 M ⊙, and V-band extinction of 4.0, which are all higher than those of the ALESS DSFGs. Based on the space density, SFR density, and stellar mass density estimates, we conclude that our ultrared sample cannot account for the majority of the star-forming progenitors of the massive, quiescent galaxies found in infrared surveys. Our sample contains the rarer, intrinsically most dusty, luminous, and massive galaxies in the early universe that will help us understand the physical drivers of extreme star formation.
Highlights
It has become clear that observing at UV/optical wavelengths is insufficient to probe the total star formation history of the universe as a large fraction of star formation is obscured by dust (e.g., Madau & Dickinson 2014; Gruppioni et al 2017)
We present a follow-up study of 300 Herschel ultrared sources from Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) and HerMES Large Mode Survey (HeLMS) with Spitzer/IRAC in combination with multiwavelength ancillary data
We have presented a large Spitzer follow-up program of 300 Herschel-selected ultrared DSFGs
Summary
It has become clear that observing at UV/optical wavelengths is insufficient to probe the total star formation history of the universe as a large fraction of star formation is obscured by dust (e.g., Madau & Dickinson 2014; Gruppioni et al 2017). A well-defined population of “ultrared” DSFGs using the Herschel SPIRE bands S500 > S350 > S250 (“500 μm risers”) has been established (e.g., Cox et al 2011; Dowell et al 2014; Asboth et al 2016; Ivison et al 2016) Based on their colors, these are likely to be z 4, dusty, and rapidly starforming (>500 Me yr−1) galaxies.
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