Letter to the Editor

LoCuSS: Shedding new light on the massive lensing cluster Abell 1689 – the view from Herschel ^*

¹ School of Physics and Astronomy, University of Birmingham, Edgbaston, B15 2TT, UK e-mail: cph@star.sr.bham.ac.uk
² Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
³ Department of Physics and Astronomy, The Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA
⁴ Rensselaer Polytechnic Institute (RPI) 110 Eighth Street, Troy, NY 12180, USA

Received: 1 April 2010
Accepted: 3 May 2010

Abstract

We present wide-field Herschel/PACS observations of A 1689, a massive galaxy cluster at z = 0.1832, from our open time key programme. We detect 39 spectroscopically confirmed 100 μm-selected cluster members down to 1.5×10¹⁰ . These galaxies are forming stars at rates in the range 1–10 /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(Hα)~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 100 μm-selected galaxies extending ~6 Mpc in length along an axis that runs NE-SW through the cluster center 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.