Measuring Type Ia Supernova Distances and Redshifts From Their Multi-band Light Curves

TL;DR

This paper demonstrates that supernova distances and redshifts can be simultaneously measured from multi-band light curves, enabling large-scale photometric surveys to determine supernova parameters without spectroscopy.

Contribution

It introduces methods to determine supernova distances and redshifts simultaneously from light curves, outlining conditions for accuracy and the impact of observational parameters.

Findings

Redshift uncertainties dominate at z~0.3 due to the steep Hubble law.

Distance-modulus uncertainties dominate at z~0.5 as the Hubble law flattens.

S/N=50 in griz bands with four-day cadence is needed to reach z=1.0 accuracy.

Abstract

The distance and redshift of a type Ia supernova can be determined simultaneously through its multi-band light curves. This fact may be used for imaging surveys that discover and obtain photometry for large numbers of supernovae; so many that it would be difficult to obtain a spectroscopic redshift for each. Using available supernova-analysis tools we find that there are several conditions in which a viable distance-redshift can be determined. Uncertainties in the effective distance at z~0.3 are dominated by redshift uncertainties coupled with the steepness of the Hubble law. By z~0.5 the Hubble law flattens out and distance-modulus uncertainties dominate. Observations that give S/N=50 at peak brightness and a four-day observer cadence in each of griz-bands are necessary to match the intrinsic supernova magnitude dispersion out to z=1.0. Lower S/N can be tolerated with the addition of redshift priors (e.g. from a host-galaxy photometric redshift), observations in an additional redder band, or by focusing on supernova redshifts that have particular leverage for this measurement. More stringent S/N requirements are anticipated as improved systematics control over intrinsic color, metallicity, and dust is attempted to be drawn from light curves.