Far-infrared spectroscopy of a lensed starburst: a blind redshift from Herschel

TL;DR

This paper reports the first blind redshift measurement of a lensed starburst galaxy using Herschel far-infrared spectroscopy, demonstrating the potential of the method for studying high-redshift dusty galaxies.

Contribution

It presents a novel approach to determine redshifts of dusty galaxies using Herschel's SPIRE FTS without prior optical identification, highlighting its effectiveness.

Findings

Secure redshift of z=1.68 via [C II] detection

Confirmation of redshift with CO line detections

Demonstration of Herschel's capability to probe high-redshift starbursts

Abstract

We report the redshift of HATLAS J132427.0+284452 (hereafter HATLAS J132427), a gravitationally lensed starburst galaxy, the first determined 'blind' by the Herschel Space Observatory. This is achieved via the detection of [C II] consistent with z = 1.68 in a far-infrared spectrum taken with the SPIRE Fourier Transform Spectrometer. We demonstrate that the [C II] redshift is secure via detections of CO J = 2 - 1 and 3 - 2 using the Combined Array for Research in Millimeter-wave Astronomy and the Institut de Radioastronomie Millimetrique's Plateau de Bure Interferometer. The intrinsic properties appear typical of high-redshift starbursts despite the high lensing-amplified fluxes, proving the ability of the FTS to probe this population with the aid of lensing. The blind detection of [C II] demonstrates the potential of the SAFARI imaging spectrometer, proposed for the much more sensitive SPICA mission, to determine redshifts of multiple dusty galaxies simultaneously without the benefit of lensing.