Abstract
The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) was a multi-cycle treasury program on the Hubble Space Telescope (HST) that surveyed a total area of ∼0.25 deg2 with ∼900 HST orbits spread across five fields over three years. Within these survey images we discovered 65 supernovae (SNe) of all types, out to z ∼ 2.5. We classify ∼24 of these as Type Ia SNe (SNe Ia) based on host galaxy redshifts and SN photometry (supplemented by grism spectroscopy of six SNe). Here we present a measurement of the volumetric SN Ia rate as a function of redshift, reaching for the first time beyond z = 2 and putting new constraints on SN Ia progenitor models. Our highest redshift bin includes detections of SNe that exploded when the universe was only ∼3 Gyr old and near the peak of the cosmic star formation history. This gives the CANDELS high redshift sample unique leverage for evaluating the fraction of SNe Ia that explode promptly after formation (<500 Myr). Combining the CANDELS rates with all available SN Ia rate measurements in the literature we find that this prompt SN Ia fraction is , consistent with a delay time distribution that follows a simple t−1 power law for all times t > 40 Myr. However, mild tension is apparent between ground-based low-z surveys and space-based high-z surveys. In both CANDELS and the sister HST program CLASH (Cluster Lensing And Supernova Survey with Hubble), we find a low rate of SNe Ia at z > 1. This could be a hint that prompt progenitors are in fact relatively rare, accounting for only 20% of all SN Ia explosions—though further analysis and larger samples will be needed to examine that suggestion.
Highlights
The prevailing model for a Type Ia supernova (SN Ia) progenitor system begins with a binary system in which the primary star evolves to become a white dwarf (WD)
We have presented a sample of 65 SNe from the five Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) fields
This sample, collected in concert with the Cluster Lensing and Supernovae search with Hubble (CLASH) SN search, is the first to extend SN Ia detections beyond z = 2, and the first to detect SNe at z ∼ 1.5 in rest-frame optical bands
Summary
The prevailing model for a Type Ia supernova (SN Ia) progenitor system begins with a binary system in which the primary star evolves to become a white dwarf (WD). The Cluster Supernova Survey (CSS) of the Supernova Cosmology Project used HST+ACS to measure the volumetric SN Ia rate (Barbary et al 2012) These data revealed a similar peak and decline, with even larger uncertainty in the high-z bins. This SN survey is a joint operation of two HST Multi-Cycle Treasury (MCT) programs: the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS; PIs: Faber and Ferguson; Grogin et al 2011; Koekemoer et al 2011), and the Cluster Lensing and Supernovae search with Hubble (CLASH; PI: Postman; Postman et al 2012).
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