Molecular content of a type-Ia SN host galaxy at z=0.6
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 Msol/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 LB*), with a small residual star-formation activity (0.2 Msol/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 AV ~ 4) or this galaxy is passive or anemic and this flux might be associated with a background galaxy.
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