A submillimetre-bright z~3 overdensity behind a z~1 supercluster revealed by SCUBA-2 and Herschel

TL;DR

This study uncovers a significant overdensity of submillimetre galaxies at z~3 behind a supercluster at z=0.9, suggesting a potential protocluster or lensed systems with high star formation rates.

Contribution

It reports the discovery of a z~3 overdensity of bright SMGs behind a supercluster, using SCUBA-2 and Herschel data, indicating a possible protocluster or lensed galaxy system.

Findings

Overdensity of SMGs exceeds average by a factor of 4.5.

Estimated redshifts of SMGs are between 2.5 and 3.5.

SMGs exhibit high star formation rates of 500-2500 solar masses per year.

Abstract

We present a wide-field (30' diameter) 850um SCUBA-2 map of the spectacular three-component merging supercluster, RCS 231953+00, at z=0.9. The brightest submillimetre galaxy (SMG) in the field (S_850=12mJy) is within 30" of one of the cluster cores (RCS 2319-C), and is likely to be a more distant, lensed galaxy. Interestingly, the wider field around RCS 2319-C reveals a local overdensity of SMGs, exceeding the average source density by a factor of 4.5, with a <1 per cent chance of being found in a random field. Utilizing Herschel-SPIRE observations, we find three of these SMGs have similar submillimetre colours. We fit their observed 250-850um spectral energy distributions to estimate their redshift, yielding 2.5<z<3.5, and calculate prodigious star formation rates (SFRs) ranging from 500-2500 solar masses per year. We speculate that these galaxies are either lensed SMGs, or signpost a physical structure at z~3: a 'protocluster' inhabited by young galaxies in a rapid phase of growth, destined to form the core of a massive galaxy cluster by z=0.