The Pantheon+ Analysis: Dependence of Cosmological Constraints on Photometric-Zeropoint Uncertainties of Supernova Surveys

Abstract

Type Ia supernovae (SNe Ia) measurements of the Hubble constant, H${}_0$, the cosmological mass density, ${\Omega }_M$, and the dark energy equation-of-state parameter, $w$, rely on numerous SNe surveys using distinct photometric systems across three decades of observation. Here, we determine the sensitivities of the upcoming SH0ES+Pantheon+ constraints on H${}_0$, ${\Omega }_M$, and $w$ to unknown systematics in the relative photometric zeropoint calibration between the 17 surveys that comprise the Pantheon+ supernovae data set. Varying the zeropoints of these surveys simultaneously with the cosmological parameters, we determine that the SH0ES+Pantheon+ measurement of H${}_0$ is robust against inter-survey photometric miscalibration, but that the measurements of ${\Omega }_M$ and $w$ are not. Specifically, we find that miscalibrated inter-survey systematics could represent a source of uncertainty in the measured value of H${}_0$ that is no larger than $0.2$ km s${}^{-1}$ Mpc${}^{-1}$. This modest increase in H${}_0$ uncertainty could not account for the $7$ km s${}^{-1}$ Mpc${}^{-1}$ "Hubble Tension" between the SH0ES measurement of H${}_0$ and the Planck $\Lambda$CDM-based inference of H${}_0$. However, we find that the SH0ES+Pantheon+ best-fit values of ${\Omega }_M$ and $w$ respectively slip, to first order, by $0.04$ and $-0.17$ per $25$ mmag of inter-survey calibration uncertainty, underscoring the vital role that cross-calibration plays in accurately measuring these parameters. Because the Pantheon+ compendium contains many surveys that share low-$z$ Hubble Flow and Cepheid-paired SNe, the SH0ES+Pantheon+ joint constraint of H${}_0$ is robust against inter-survey photometric calibration errors, and such errors do not represent an impediment to jointly using SH0ES+Pantheon+ to measure H${}_0$ to 1% accuracy.

Submitted to ApJ. Comments welcome

References in corpus (2)

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• Evaluating the Calibration of SN Ia Anchor Datasets with a Bayesian Hierarchical Model

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