Survival of Massive Star-forming Galaxies in Cluster Cores Drives Gas-phase Metallicity Gradients: The Effects of Ram Pressure Stripping

Abstract

Recent observations of galaxies in a cluster at z  = 0.35 show that their integrated gas-phase metallicities increase with decreasing cluster-centric distance. To test whether ram pressure stripping (RPS) is the underlying cause, we use a semianalytic model to quantify the “observational bias” that RPS introduces into the aperture-based metallicity measurements. We take integral field spectroscopy of local galaxies, remove gas from their outer galactic disks via RPS, and then conduct mock slit observations of cluster galaxies at z  = 0.35. Our RPS model predicts a typical cluster-scale metallicity gradient of −0.03 dex/Mpc. By removing gas from the outer galactic disks, RPS introduces a mean metallicity enhancement of + 0.02 dex at a fixed stellar mass. This gas removal and subsequent quenching of star formation preferentially removes low-mass cluster galaxies from the observed star-forming population. As only the more massive star-forming galaxies survive to reach the cluster core, RPS produces a cluster-scale stellar mass gradient of − 0.05 log ( M * / M ⊙ ) /Mpc. This mass segregation drives the predicted cluster-scale metallicity gradient of −0.03 dex/Mpc. However, the effects of RPS alone cannot explain the higher metallicities measured in cluster galaxies at z  = 0.35. We hypothesize that additional mechanisms including steep internal metallicity gradients and self-enrichment due to gas strangulation are needed to reproduce our observations at z  = 0.35.