Evidence for a Population of High‐Redshift Submillimeter Galaxies from Interferometric Imaging

TLDR

The Submillimeter Array imaged a flux‑limited sample of seven 1.1‑mm selected galaxies in COSMOS at 890 µm with ~2″ resolution. All seven galaxies are bright, compact point sources with precise positions, and the five radio‑dim members exhibit higher submillimeter‑to‑radio ratios, fainter IRAC fluxes, lack 24 µm detections, and sub‑arcsecond sizes, indicating they are very dusty, high‑redshift starbursts comparable in scale to local ULIRGs.

Abstract

We have used the Submillimeter Array to image a flux-limited sample of seven submillimeter galaxies, selected by the AzTEC camera on the JCMT at 1.1 mm, in the COSMOS field at 890 μ m with ~2'' resolution. All of the sources—two radio-bright and five radio-dim—are detected as single point sources at high significance (>6 σ), with positions accurate to ~0.2'' that enable counterpart identification at other wavelengths observed with similarly high angular resolution. All seven have IRAC counterparts, but only two have secure counterparts in deep HST ACS imaging. As compared to the two radio-bright sources in the sample, and those in previous studies, the five radio-dim sources in the sample (1) have systematically higher submillimeter-to-radio flux ratios, (2) have lower IRAC 3.6-8.0 μ m fluxes, and (3) are not detected at 24 μ m . These properties, combined with size constraints at 890 μ m (θ ≲ 1.2''), suggest that the radio-dim submillimeter galaxies represent a population of very dusty starbursts, with physical scales similar to local ultraluminous infrared galaxies, with an average redshift higher than radio-bright sources.