WALLABY pilot survey: first look at the Hydra I cluster and ram pressure stripping of ESO 501−G075

Abstract

We present results from neutral atomic hydrogen (H i) 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 H i 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 H i morphology of ESO 501−G075. We rule out tidal interactions, as ESO 501−G075 has no nearby neighbours within ∼0.34 Mpc. We use a simple model to determine that ram pressure can remove gas from the disc at radii r ≳ 25 kpc. We conclude that, as ESO 501−G075 has a typical H i 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.

WALLABY Pilot Survey: The Diversity of Ram Pressure Stripping of the Galactic H i Gas in the Hydra Cluster

“…At least for the resolved galaxies ( ) once onset, RPS is likely a slow process (600 Myr) for depleting the existing reservoir of H I in the galaxies. This is because for the H I-rich galaxies with extended H I disks, RPS can start at a relatively large cluster-centric distance ( d r 1.25 proj 200 , see Reynolds et al 2021 for a detailed analysis for one such galaxy), where the ram pressure changes slowly with clustercentric distance. The different d proj for RPS to onset and the different speeds at which f RPS rises as a function of d proj may partly explain the scatter of quenching speed 14 found for the SFR of cluster galaxies in the literature (Wetzel et al 2013;Haines et al 2015;Boselli et al 2016).…”

“…Detailed analysis of RPS in ESO 501-G075 (239 in Figure 10, WALLABY ID: J103655-265412) can be found in Reynolds et al (2021).…”

WALLABY Pilot Survey: Public release of HI kinematic models for more than 100 galaxies from phase 1 of ASKAP pilot observations

“…We judge the outer deprojected surface densities and HI sizes to be robust enough for use in many cases, although HI sizes should be first corrected for beam smearing (e.g. Wang et al 2021;Reynolds et al 2021). In the future, the custom WALLABY pipeline will fit the surface density using the full 3D cube and so, should be more accurate than the ellipse fitting adopted here.…”

WALLABY Pilot Survey: HI gas disc truncation and star formation of galaxies falling into the Hydra I cluster

“…The WALLABY pilot survey observations of the Hydra field cover 60 square degrees extending over 10:03:00 < 𝛼 (J2000) < 10:53:01 and −30:30:00 < 𝛿 (J2000) < −24:30:00. We refer the reader to the following WALLABY publications for details of the WALLABY pilot survey observations of the Hydra I cluster: Reynolds et al (2021); Wang et al (2021) and ASKAP/WALLABY data reduction process: Elagali et al (2019); For et al (2019); Kleiner et al (2019); Lee-Waddell et al (2019); Reynolds et al (2019). The final H spectral line cube has a synthesised beam size of 30×30 arcsec, spectral resolution of 4 km s −1 and an average root-mean-square (rms) sensitivity of ∼ 2.0 mJy per beam per 4 km s −1 over the cube.…”

“…These data have been used for the detailed study of individual objects (e.g. ESO 501−G075, Reynolds et al 2021) and larger population studies (e.g. ram pressure of galaxies within ∼ 2.5𝑅 200 , Wang et al 2021).…”