Photometric Identification of Type Ia Supernovae at Moderate Redshift

Abstract

Large photometric surveys with the aim of identifying many Type Ia supernovae (SNe) at moderate redshift are challenged in separating these SNe from other SN types. We are motivated to identify Type Ia SNe based only on broadband photometric information, since spectroscopic determination of the SN type, the traditional method, requires significant amounts of time on large telescopes. We consider the possible observables provided by a large synoptic photometry survey. We examine the optical colors and magnitudes of many SN types from z=0.1 to z=1.0, using space-based ultraviolet spectra and ground-based optical spectra to simulate the photometry. We also discuss the evolution of colors over the SN outburst and the use of host galaxy characteristics to aid in the identification of Type Ia SNe. We consider magnitudes in both the SDSS photometric system and in a proposed filter system with logarithmically spaced bandpasses. We find that photometric information in four bands covering the entire optical spectrum appears capable of providing identification of Type Ia SNe based on their colors at a single observed epoch soon after maximum light, even without independent estimates of the SN redshift. Very blue filters are extremely helpful, as at moderate redshift they sample the restframe ultraviolet spectrum where the SN types are very different. We emphasize the need for further observations of SNe in the restframe ultraviolet to fully characterize, refine, and improve this method of SN type identification.