Massive Early-type Galaxies in the HSC-SSP: Flux Fraction of Tidal Features and Merger Rates

Abstract

Abstract Here we present a statistical study on tidal features around massive early-type galaxies (ETGs). Utilizing the imaging data of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP), we measure the flux fraction of tidal features (f tidal) in 2649 ETGs with stellar mass M * > 1011 M ⊙ and redshift 0.05 < z < 0.15 using automated techniques. The Wide layer of HSC-SSP reaches a depth of ∼28.5 mag arcsec−2 in the i band. Under this surface brightness limit, we find that about 28% of these galaxies harbor prominent tidal features with f tidal > 1%, among which the number of ETGs decreases exponentially with f tidal, with a logarithmic slope of ∼100. Within the stellar mass range we probe, we note that f tidal increases by a factor of 2 from M * ≈ 1011 to 1012 M ⊙. We also perform a pair count to estimate the merger rate of these massive ETGs. Combining the merger rates with f tidal, we estimate that the typical lifetime of tidal features is ∼3 Gyr, consistent with previous studies.