WALLABY Pilot Survey: the Potential Polar Ring Galaxies NGC~4632 and NGC~6156

TL;DR

This paper reports the discovery of two potential polar ring galaxies in the WALLABY survey, using HI observations and 3D modeling, suggesting WALLABY could detect hundreds of such galaxies if confirmed.

Contribution

It introduces the first HI-based identification of potential polar ring galaxies in WALLABY data and assesses their detectability and incidence rate.

Findings

Two candidate PRGs identified with ~50% anomalous gas content

3D kinematic models are consistent with PRG characteristics

Estimated 1-3% incidence rate implies hundreds of detections in WALLABY

Abstract

We report on the discovery of two potential polar ring galaxies (PRGs) in the WALLABY Pilot Data Release 1 (PDR1). These untargetted detections, cross-matched to NGC 4632 and NGC 6156, are some of the first galaxies where the Hi observations show two distinct components. We used the iDaVIE virtual reality software to separate the anomalous gas from the galactic gas and find that the anomalous gas comprises ~ 50% of the total H i content of both systems. We have generated plausible 3D kinematic models for each galaxy assuming that the rings are circular and inclined at 90 degrees to the galaxy bodies. These models show that the data are consistent with PRGs, but do not definitively prove that the galaxies are PRGs. By projecting these models at different combinations of main disk inclinations, ring orientations, and angular resolutions in mock datacubes, we have further investigated the detectability of similar PRGs in WALLABY. Assuming that these galaxies are indeed PRGs, the detectability fraction, combined with the size distribution of WALLABY PDR1 galaxies, implies an incidence rate of ~ 1% - 3%. If this rate holds true, the WALLABY survey will detect hundreds of new polar ring galaxies.