Abstract
We present the discovery of a Type Ia supernova (SN) at redshift $z = 1.914$ from the CANDELS multi-cycle treasury program on the \textit{Hubble Space Telescope (HST)}. This SN was discovered in the infrared using the Wide-Field Camera 3, and it is the highest-redshift Type Ia SN yet observed. We classify this object as a SN\,Ia by comparing its light curve and spectrum with those of a large sample of Type Ia and core-collapse supernovae (SNe). Its apparent magnitude is consistent with that expected from the $\Lambda$CDM concordance cosmology. We discuss the use of spectral evidence for classification of $z > 1.5$ SNe\,Ia using {\it HST} grism simulations, finding that spectral data alone can frequently rule out SNe\,II, but distinguishing between SNe\,Ia and SNe\,Ib/c can require prohibitively long exposures. In such cases, a quantitative analysis of the light curve may be necessary for classification. Our photometric and spectroscopic classification methods can aid the determination of SN rates and cosmological parameters from the full high-redshift CANDELS SN sample.
Highlights
Over the past decade, measurements of Type Ia supernovae (SNe) at redshift z 1 have extended the observed population to a time when the universe was matter dominated (Riess et al 2001, 2004, 2007; Suzuki et al 2012; Rodney et al 2012; Rubin et al 2013)
In this paper we present observations of a SN Ia at z = 1.91 (SN UDS10Wil), the highest-redshift SN Ia discovered to date
SN UDS10Wil was discovered in the second epoch of CANDELS observations of the UKIDSS Ultra-Deep Survey field (UDS; Lawrence et al 2007; Cirasuolo et al 2007) on 2010 December 30, after subtracting the images obtained in the first epoch (2010 November 11)
Summary
Measurements of Type Ia supernovae (SNe) at redshift z 1 have extended the observed population to a time when the universe was matter dominated (Riess et al 2001, 2004, 2007; Suzuki et al 2012; Rodney et al 2012; Rubin et al 2013) At these lookback times of 7 Gyr, the predicted effects of dark energy are small, while the typical conditions under which SNe form are increasingly different from local environments. These characteristics may allow observations at high redshift to constrain an evolutionary change in SN Ia brightness independent of our understanding of dark energy This type of systematic shift in magnitude could be caused by changing metallicity or progenitor masses (e.g., Domınguez et al 2001).
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