Two Type Ia Supernovae at Redshift ~2 : Improved Classification and Redshift Determination with Medium-band Infrared Imaging

TL;DR

This paper demonstrates that medium-band infrared imaging with HST improves classification and redshift determination of high-redshift Type Ia supernovae, enabling more efficient cosmological measurements.

Contribution

The study introduces a medium-band infrared imaging technique that enhances supernova classification and redshift estimation at high redshift, offering a less resource-intensive alternative to spectroscopy.

Findings

Two high-redshift Type Ia SNe discovered and classified.

Medium-band imaging improves redshift accuracy and classification.

Method is insensitive to dust and host galaxy contamination.

Abstract

We present two supernovae (SNe) discovered with the Hubble Space Telescope (HST) in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), an HST multi-cycle treasury program. We classify both objects as Type Ia SNe and find redshifts of z = 1.80+-0.02 and 2.26 +0.02 -0.10, the latter of which is the highest redshift Type Ia SN yet seen. Using light curve fitting we determine luminosity distances and find that both objects are consistent with a standard Lambda-CDM cosmological model. These SNe were observed using the HST Wide Field Camera 3 infrared detector (WFC3-IR), with imaging in both wide- and medium-band filters. We demonstrate that the classification and redshift estimates are significantly improved by the inclusion of single-epoch medium-band observations. This medium-band imaging approximates a very low resolution spectrum (lambda/delta lambda ~ 100) which can isolate broad spectral absorption features that differentiate Type Ia SNe from their most common core collapse cousins. This medium-band method is also insensitive to dust extinction and (unlike grism spectroscopy) it is not affected by contamination from the SN host galaxy or other nearby sources. As such, it can provide a more efficient - though less precise - alternative to IR spectroscopy for high-z SNe.