Spectroscopic identification of a redshift 1.55 supernova host galaxy from the Subaru Deep Field Supernova Survey

TL;DR

This study spectroscopically confirmed the redshift and classification of a high-redshift supernova host galaxy, demonstrating the effectiveness of wide spectral range observations in accurately identifying supernovae and their host properties.

Contribution

We obtained the first robust spectroscopic redshift and classification of a z > 1.5 supernova host galaxy using VLT/X-shooter, confirming photometric estimates and ruling out AGN contamination.

Findings

Spectroscopic redshift of 1.54563 ± 0.00027 for the host galaxy

Host galaxy properties consistent with the fundamental metallicity relation

Confirmed the transient as a supernova, not an active galactic nucleus

Abstract

Context: The Subaru Deep Field (SDF) Supernova Survey discovered 10 Type Ia supernovae (SNe Ia) in the redshift range 1.5<z<2.0, as determined solely from photometric redshifts of the host galaxies. However, photometric redshifts might be biased, and the SN sample could be contaminated by active galactic nuclei (AGNs). Aims: We aim to obtain the first robust redshift measurement and classification of a z > 1.5 SDF SN Ia host galaxy candidate Methods: We use the X-shooter (U-to-K-band) spectrograph on the Very Large Telescope to allow the detection of different emission lines in a wide spectral range. Results: We measure a spectroscopic redshift of 1.54563 +/- 0.00027 of hSDF0705.25, consistent with its photometric redshift of 1.552 +/- 0.018. From the strong emission-line spectrum we rule out AGN activity, thereby confirming the optical transient as a SN. The host galaxy follows the fundamental metallicity relation defined in Mannucci et al. (2010, 2011) showing that the properties of this high-redshift SN Ia host galaxy is similar to other field galaxies. Conclusions: Spectroscopic confirmation of additional SDF SN hosts would be required to confirm the cosmic SN rate evolution measured in the SDF.