How Sky Subtraction Scales Affect Intracluster Light Measurements

Deep imaging surveys are opening a new window on the low surface brightness universe. However, the recovery of diffuse emission depends on the survey depth and how the sky background is treated. Estimating the sky on scales comparable to astrophysical sources risks biasing flux measurements. This effect is particularly significant for intracluster light (ICL), the most extended diffuse baryonic component of galaxy clusters. We show in a M 500 – z plane that the sky subtraction scales employed in the Legacy Survey of Space and Time (LSST) Data Preview 2 and Hyper Suprime-Cam Public Data Release 3 (HSC-PDR3) impact clusters with M 500 ≳ 10 13.4 M ⊙ at all redshifts, whereas HSC-PDR2 only oversubtracts the most massive systems at z < 0.1. The larger sky subtraction scale anticipated for the full LSST survey will mitigate this bias.