LoCuSS: Shedding New Light on the Massive Lensing Cluster Abell 1689 - The View From Herschel

TL;DR

This study uses Herschel observations to analyze star-forming galaxies in Abell 1689, revealing two distinct populations and evidence of cluster substructure, indicating a dynamically active merging system.

Contribution

First detailed Herschel/PACS analysis of Abell 1689's star-forming galaxies, identifying two populations and linking substructure to cluster dynamics.

Findings

Two-thirds of galaxies are blue, late-type spirals with unobscured star formation.

One-third are dusty red galaxies with obscured star formation, mainly in outskirts.

Detected an extended galaxy excess aligned with cluster substructure.

Abstract

We present wide-field Herschel/PACS observations of Abell 1689, a massive galaxy cluster at z=0.1832, from our Open Time Key Programme. We detect 39 spectroscopically confirmed 100micron-selected cluster members down to 1.5x10^10 Lsun. These galaxies are forming stars at rates in the range 1-10 Msun/yr, and appear to comprise two distinct populations: two-thirds are unremarkable blue, late-type spirals found throughout the cluster; the remainder are dusty red sequence galaxies whose star formation is heavily obscured with A(Halpha)~2 mag, and are found only in the cluster outskirts. The specific-SFRs of these dusty red galaxies are lower than the blue late-types, suggesting that the former are in the process of being quenched, perhaps via pre-processing, the unobscured star formation being terminated first. We also detect an excess of 100micron-selected galaxies extending ~6 Mpc in length along an axis that runs NE-SW through the cluster centre at >95% confidence. Qualitatively this structure is consistent with previous reports of substructure in X-ray, lensing, and near-infrared maps of this cluster, further supporting the view that this cluster is a dynamically active, merging system.