H-ATLAS: A Candidate High Redshift Cluster/Protocluster of Star-Forming Galaxies

TL;DR

This study identifies a potential high-redshift galaxy cluster or protocluster around a gravitationally lensed galaxy at z=3.26, revealing a significant overdensity of star-forming galaxies using multi-wavelength submillimeter and infrared data.

Contribution

It presents the discovery of a candidate high-redshift protocluster with multiple starburst galaxies, utilizing combined Herschel, LABOCA, SCUBA2, SMA, and Spitzer observations for detailed analysis.

Findings

Detected 17 bright submm sources near the lensed galaxy

Identified several sources with redder colours indicating high redshift

Localized one companion with SMA, confirming its high-redshift nature

Abstract

We investigate the region around the Planck-detected z=3.26 gravitationally lensed galaxy HATLAS J114637.9-001132 (hereinafter HATLAS12-00) using both archival Herschel data from the H-ATLAS survey and using submm data obtained with both LABOCA and SCUBA2. The lensed source is found to be surrounded by a strong overdensity of both Herschel-SPIRE sources and submm sources. We detect 17 bright (S_870 >~7 mJy) sources at >4sigma closer than 5 arcmin to the lensed object at 850/870 microns. Ten of these sources have good cross-identifications with objects detected by Herschel-SPIRE which have redder colours than other sources in the field, with 350 micron flux > 250 micron flux, suggesting that they lie at high redshift. Submillimeter Array (SMA) observations localise one of these companions to ~1 arcsecond, allowing unambiguous cross identification with a 3.6 and 4.5 micron Spitzer source. The optical/near-IR spectral energy distribution (SED) of this source is measured by further observations and found to be consistent with z>2, but incompatible with lower redshifts. We conclude that this system may be a galaxy cluster/protocluster or larger scale structure that contains a number of galaxies undergoing starbursts at the same time.