WALLABY Pilot Survey: First Look at the Hydra I Cluster and Ram Pressure Stripping of ESO 501-G075

TL;DR

This paper presents initial results from WALLABY HI observations of the Hydra I cluster, identifying ram pressure stripping effects on galaxy ESO 501-G075 near the cluster's virial radius, indicating early-stage infall.

Contribution

First demonstration of WALLABY's final survey sensitivity and spatial resolution in detecting environmental effects like ram pressure stripping in galaxy clusters.

Findings

WALLABY can reach its final survey sensitivity.

ESO 501-G075 exhibits HI tail and morphological asymmetry.

Ram pressure can strip gas at radii >25 kpc in the galaxy.

Abstract

We present results from neutral atomic hydrogen (HI) observations of Hydra I, the first cluster observed by the Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY) on the Australian Square Kilometre Array Pathfinder. For the first time we show that WALLABY can reach its final survey sensitivity. Leveraging the sensitivity, spatial resolution and wide field of view of WALLABY, we identify a galaxy, ESO 501-G075, that lies near the virial radius of Hydra I and displays an HI tail. ESO 501-G075 shows a similar level of morphological asymmetry as another cluster member, which lies near the cluster centre and shows signs of experiencing ram pressure. We investigate possible environmental processes that could be responsible for producing the observed disturbance in the HI morphology of ESO 501-G075. We rule out tidal interactions, as ESO 501-G075 has no nearby neighbours within $\sim0.34$Mpc. We use a simple model to determine that ram pressure can remove gas from the disc at radii $r\gtrsim25$kpc. We conclude that, as ESO 501-G075 has a typical HI mass compared to similar galaxies in the field and its morphology is compatible with a ram pressure scenario, ESO 501-G075 is likely recently infalling into the cluster and in the early stages of experiencing ram pressure.