WALLABY Pilot Survey: the diversity of ram pressure stripping of the galactic HI gas in the Hydra Cluster

TL;DR

This paper investigates how ram pressure stripping affects HI gas in Hydra Cluster galaxies, revealing that many are in early stripping stages with slow overall HI depletion, providing insights into galaxy evolution in clusters.

Contribution

It presents the first detailed analysis of HI gas stripping stages and timescales in Hydra Cluster galaxies using WALLABY survey data, highlighting the diversity of stripping processes.

Findings

Nearly two thirds of galaxies within 1.25$r_{200}$ are in early ram pressure stripping stages.

Most galaxies are only weakly stripped, with less than 90% of HI mass being affected.

It takes less than 200 Myr to remove the currently strippable HI, but over 600 Myr to significantly reduce total HI mass.

Abstract

This study uses HI image data from the WALLABY pilot survey with the ASKAP telescope, covering the Hydra cluster out to 2.5$r_{200}$. We present the projected phase-space distribution of HI-detected galaxies in Hydra, and identify that nearly two thirds of the galaxies within $1.25r_{200}$ may be in the early stages of ram pressure stripping. More than half of these may be only weakly stripped, with the ratio of strippable HI (i.e., where the galactic restoring force is lower than the ram pressure in the disk) mass fraction (over total HI mass) distributed uniformly below 90%. Consequently, the HI mass is expected to decrease by only a few 0.1 dex after the currently strippable portion of HI in these systems has been stripped. A more detailed look at the subset of galaxies that are spatially resolved by WALLABY observations shows that, while it typically takes less than 200 Myr for ram pressure stripping to remove the currently strippable portion of HI, it may take more than 600 Myr to significantly change the total HI mass. Our results provide new clues to understanding the different rates of HI depletion and star formation quenching in cluster galaxies.