Molecular content of a type-Ia SN host galaxy at z=0.6

TL;DR

This study investigates the molecular content and star formation activity of a z=0.6 type-Ia supernova host galaxy, finding little cold gas and low residual star formation, suggesting it is a passive or possibly obscured galaxy.

Contribution

First to analyze the molecular content of a type-Ia supernova host at this redshift using CO observations and optical data, revealing low gas content and star formation.

Findings

No CO emission detected, indicating little cold gas.

Star formation rate estimated to be below 50 solar masses per year.

Galaxy likely passive or obscured, with no evidence of active starburst or AGN.

Abstract

We study the properties and the molecular content of the host of a type-Ia supernova (SN1997ey). This z=0.575 host is the brightest submillimetre source of the sample of type-Ia supernova hosts observed at 450um and 850um by Farrah et al.. Observations were performed at IRAM-30m to search for CO(2-1) and CO(3-2) lines in good weather conditions but no signal was detected. The star formation rate cannot exceed 50 M_sol/yr. These negative results are confronted with an optical analysis of a Keck spectrum and other data archives. We reach the conclusion that this galaxy is a late-type system (0.7 L^B_*), with a small residual star-formation activity (0.2 M_sol/yr) detected in the optical. No source of heating (AGN or starburst) is found to explain the submillimetre-continuum flux and the non-CO detection excludes the presence of a large amount of cold gas. We thus suggest that either the star formation activity is hidden in the nucleus (with A_V ~ 4) or this galaxy is passive or anemic and this flux might be associated with a background galaxy.