Deep Herschel view of obscured star formation in the Bullet cluster

TL;DR

This study uses Herschel data to measure obscured star formation rates in the Bullet cluster and a background system, revealing discrepancies between FIR-based and 24um-based SFR estimates for some galaxies.

Contribution

It provides the first comprehensive FIR-based star formation rates for the Bullet cluster and compares them with 24um estimates, highlighting limitations of existing templates.

Findings

Herschel detects 23 Bullet cluster members with total SFR_FIR of 144 solar masses per year.

Background system has ~50% higher SFR_FIR than the cluster.

SFR_24 underestimates SFR_FIR in ~40% of galaxies due to excess in observed flux ratios.

Abstract

We use deep, five band (100-500um) data from the Herschel Lensing Survey (HLS) to fully constrain the obscured star formation rate, SFR_FIR, of galaxies in the Bullet cluster (z=0.296), and a smaller background system (z=0.35) in the same field. Herschel detects 23 Bullet cluster members with a total SFR_FIR = 144 +/- 14 M_sun yr^-1. On average, the background system contains brighter far-infrared (FIR) galaxies, with ~50% higher SFR_FIR (21 galaxies; 207 +/- 9 M_sun yr^-1). SFRs extrapolated from 24um flux via recent templates (SFR_24) agree well with SFR_FIR for ~60% of the cluster galaxies. In the remaining ~40%, SFR_24 underestimates SFR_FIR due to a significant excess in observed S_100/S_24 (rest frame S_75/S_18) compared to templates of the same FIR luminosity.