Lower bounds on photometric redshift errors from Type Ia supernovae templates

TL;DR

This paper develops a template-based photometric redshift estimator for Type Ia supernovae and derives lower bounds on redshift errors, highlighting limitations for future cosmological surveys.

Contribution

It introduces a new method to estimate redshift errors from photometry alone and quantifies the fundamental limits on cosmological parameter measurements.

Findings

Redshift errors set lower bounds on cosmological parameter accuracy.

Photometric redshift errors significantly impact supernova-based cosmology.

Systematic errors combined with photometric uncertainties constrain survey capabilities.

Abstract

Cosmology with Type Ia supernovae heretofore has required extensive spectroscopic follow-up to establish a redshift. Though tolerable at the present discovery rate, the next generation of ground-based all-sky survey instruments will render this approach unsustainable. Photometry-based redshift determination is a viable alternative, but introduces non-negligible errors that ultimately degrade the ability to discriminate between competing cosmologies. We present a strictly template-based photometric redshift estimator and compute redshift reconstruction errors in the presence of photometry and statistical errors. With reasonable assumptions for a cadence and supernovae distribution, these redshift errors are combined with systematic errors and propagated using the Fisher matrix formalism to derive lower bounds on the joint errors in $\Omega_w$ and $\Omega_w'$ relevant to the next generation of ground-based all-sky survey.