A bright, dust-obscured, millimeter-selected galaxy beyond the Bullet Cluster (1E0657-56)

TL;DR

This paper reports the discovery of a bright, dust-obscured galaxy at redshift 2.7 behind the Bullet Cluster, magnified by gravitational lensing, revealing insights into faint millimeter galaxy populations.

Contribution

First detection of a highly magnified, dust-obscured galaxy behind the Bullet Cluster using 1.1 mm observations, demonstrating the potential of lensing clusters to study faint millimeter galaxies.

Findings

Galaxy at z=2.7 with S_1.1mm=15.9 mJy detected

Magnification factor >20 due to lensing

Rest-frame FIR luminosity ≤ 10^12 L_sun, characteristic of LIRGs

Abstract

Deep 1.1 mm continuum observations of 1E0657-56 (the "Bullet Cluster") taken with the millimeter-wavelength camera AzTEC on the 10-m Atacama Submillimeter Telescope Experiment (ASTE), have revealed an extremely bright (S$_{\rm{1.1mm}}=15.9$ mJy) unresolved source. This source, MMJ065837-5557.0, lies close to a maximum in the density of underlying mass-distribution, towards the larger of the two interacting clusters as traced by the weak-lensing analysis of Clowe et al. 2006. Using optical--IR colours we argue that MMJ065837-5557.0 lies at a redshift of $z = 2.7 \pm 0.2$. A lensing-derived mass-model for the Bullet Cluster shows a critical-line (caustic) of magnification within a few arcsecs of the AzTEC source, sufficient to amplify the intrinsic millimeter-wavelength flux of the AzTEC galaxy by a factor of $\gg 20$. After subtraction of the foreground cluster emission at 1.1mm due to the Sunyaev-Zel'dovich effect, and correcting for the magnification, the rest-frame FIR luminosity of MMJ065837-5557.0 is $\le 10^{12} \rm L_{\odot}$, characteristic of a luminous infrared galaxy (LIRG). We explore various scenarios to explain the colors, morphologies and positional offsets between the potential optical and IR counterparts, and their relationship with MMJ065837-5557.0. Until higher-resolution and more sensitive (sub)millimeter observations are available, the detection of background galaxies close to the caustics of massive lensing clusters offers the only opportunity to study this intrinsically faint millimeter-galaxy population.