Dependence of Cosmological Constraints on Gray Photometric Zero-point Uncertainties of Supernova Surveys

Abstract

Type Ia supernova (SN) measurements of the Hubble constant, H _0 ; cosmic mass density, Ω _M ; and dark energy equation-of-state parameter, w , rely on heterogeneous SN surveys across three decades of observation. These distinct surveys may have undiagnosed, relative photometric zero-point errors. We determine the sensitivities of the SH0ES+Pantheon+ cosmological constraints to unknown gray systematics in the photometric zero-point calibration between the 19 surveys that comprise the Pantheon+ SN compendium. Varying the surveys’ gray zero-points simultaneously with cosmological parameters, we determine that the SH0ES+Pantheon+ measurement of H _0 is robust against gray intersurvey photometric miscalibration. Specifically, uncalibrated intersurvey systematics could represent a source of uncertainty no larger than 0.39 km s ^−1 Mpc ^−1 for H _0 . 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 ΛCDM-based inference of H _0 . However, the SH0ES+Pantheon+ best-fit values of Ω _M and w are not robust against gray zero-point error, slipping by up to 0.16 and −0.63. Because measurements of Ω _M and w depend on intrasurvey cross-band calibration, the hypothetical gray miscalibration underestimates the sensitivity of these measurements to zero-point miscalibration. Because the Pantheon+ compendium contains many surveys that share low- z Hubble flow (HF) and Cepheid-paired SNe, intersurvey photometric calibration errors do not significantly impede the joint use of SH0ES and Pantheon+ to measure H _0 to 1% accuracy. However, H _0 constraints that rely on one HF survey but numerous galactic distance calibration surveys are susceptible to intersurvey photometric miscalibration.

Keywords

• Cosmology
• Type Ia supernovae
• Flux calibration
• Hubble constant
• Dark energy
• Astronomy data analysis