Cosmology requirements on supernova photometric redshift systematics for the Rubin LSST and Roman Space Telescope

Abstract

Some million type Ia supernovae (SN) will be discovered and monitored during upcoming wide area time domain surveys such as the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). For cosmological use, accurate redshifts are needed among other characteristics; however the vast majority of the SN will not have spectroscopic redshifts, even for their host galaxies, only photometric redshifts. We assess the redshift systematic control necessary for robust cosmology. Based on the photometric vs true redshift relation generated by machine learning applied to a simulation of 500,000 galaxies as observed with LSST quality, we quantify requirements on systematics in the mean relation and in the outlier fraction and deviance so as not to bias dark energy cosmological inference. Certain redshift ranges are particularly sensitive, motivating spectroscopic followup of SN at z ≲ 0.2 and around z ≈ 0.5-0.6. Including Nancy Grace Roman Space Telescope near infrared bands in the simulation, we reanalyze the constraints, finding improvements at high redshift but little at the low redshifts where systematics lead to strong cosmology bias. We identify a complete spectroscopic survey of SN host galaxies for z ≲ 0.2 as a highly favored element for robust SN cosmology.

The Pantheon+ analysis: Improving the redshifts and peculiar velocities of Type Ia supernovae used in cosmological analyses

“…However, with samples of greater than 1000 SNe, systematic uncertainties are of paramount concern, and potential systematic biases in the redshift measurements must be considered (e.g. Huterer et al 2004;Wojtak et al 2015;Davis et al 2019;Steinhardt, Sneppen, & Sen 2020;Mitra & Linder 2021). In this analysis, we perform a comprehensive review of the redshifts of individual SNe used in the latest samples for cosmological analyses and analyse potential biases due to issues with redshifts in the recovery of cosmological parameters.…”

The Pantheon+ Analysis: Improving the Redshifts and Peculiar Velocities of Type Ia Supernovae Used in Cosmological Analyses

“…However, with samples of greater than 1000 SNe, systematic uncertainties are of paramount concern, and potential systematic biases in the redshift measurements must be considered (e.g. Huterer et al 2004;Wojtak et al 2015;Davis et al 2019;Steinhardt et al 2020;Mitra & Linder 2021). In this analysis, we perform a comprehensive review of the redshifts of individual SNe used in the latest samples for cosmological analyses and analyze potential biases due to issues with redshifts in the recovery of cosmological parameters.…”

Swiss-cheese cosmologies with variable $G$ and $Λ$ from the renormalization group

“…The existence of allowed range of parameters at the parameter space does not guarantees the fitting quality of our models, however the non-existence implies the non-viability of our models. The full assessment of viability for our models ought to be performed using likelihood analysis and model selection methods on cosmological data-sets, such as Supernovae Ia [55][56][57][58], Baryonic Accoustic Oscillations [59] and direct measurements of the Hubble rate, in the same fashion with [33], will be resented in a forthcoming paper. This analysis is beyond the scope of the current work.…”