GALEX Spectroscopy of SN 2005ay suggests a UV spectral uniformity among type II-P supernovae

TL;DR

This study presents UV spectra of SN 2005ay, revealing a surprising uniformity among type II-P supernovae, which could enhance their use in cosmology.

Contribution

First UV spectroscopic observations of SN 2005ay, demonstrating spectral similarity among type II-P supernovae and implications for high-redshift cosmology.

Findings

UV spectra of SN 2005ay resemble SN 1999em and SN 2005cs

UV spectral evolution traced during first month after explosion

UV homogeneity suggests potential for cosmological applications

Abstract

We present the first results from our GALEX program designed to obtain ultraviolet (UV) spectroscopy of nearby core-collapse supernovae (SNe). Our first target, SN 2005ay in the nearby galaxy NGC 3938, is a typical member of the II-P SN subclass. Our spectra show remarkable similarity to those of the prototypical type II-P event SN 1999em, and resemble also Swift observations of the recent type II-P event SN 2005cs. Taken together, the observations of these three events trace the UV spectral evolution of SNe II-P during the first month after explosion, as required in order to interpret optical observations of high-redshift SNe II-P, and to derive cross-filter K-corrections. While still highly preliminary, the apparent UV homogeneity of SNe II-P bodes well for the use of these events as cosmological probes at high redshift.