A SCUBA-2 selected Herschel-SPIRE dropout and the nature of this population

Abstract

Dusty star-forming galaxies (DSFGs) detected at z > 4 provide important examples of the first generations of massive galaxies. However, few examples with spectroscopic confirmation are currently known, with Hershel struggling to detect significant numbers of z > 6 DSFGs. NGP6 D1 is a bright 850 μm source (12.3 ± 2.5 mJy) with no counterparts at shorter wavelengths (a SPIRE dropout). Interferometric observations confirm it is a single source, with no evidence for any optical or NIR emission, or nearby likely foreground lensing sources. No >3σ detected lines are seen in both LMT Redshift Search Receiver and IRAM 30 m EMIR spectra of NGP6 D1 across 32 GHz of bandwidth despite reaching detection limits of ∼ 1 mJy/500 km s−1, so the redshift remains unknown. Template fitting suggests that NGP6 D1 is most likely between z = 5.8 and 8.3. SED analysis finds that NGP6 D1 is a ULIRG, with a dust mass ∼108-109 M☉ and a star-formation rate of ∼500 M☉ yr−1. We place upper limits on the gas mass of NGP6 D1 of MH2