Deg et al. report on the discovery of two potential polar ring galaxies (PRGs) in WALLABY pilot survey data. These untargetted detections, cross-matched to NGC 4632 and NGC 6156, are some of the first galaxies where the neutral hyrdogen (HI) observations show two distinct components. Separating the anomalous gas from the galactic gas suggests that the anomalous gas comprises about half of the total HI content of both systems. The team 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. Assuming that these galaxies are indeed PRGs, the pilot survey data implies an incidence rate of 1% ~ 3%. If this rate holds true, the WALLABY survey will detect hundreds of new polar ring galaxies.

The image shows the anomalous HI component of the NGC 4632, overlaid on a composite optical image from the Hyper Suprime-Cam Subaru Strategic Program. The white bar at the bottom-left of the image shows the angular size scale. The anomalous gas clearly has a different orientation from that of the stellar disk. The HI intensity map in this figure is created by binning velocity channels together into several individual intensity maps, assigning a colour to each individual map, and blending them into one image. This retains some velocity information while rendering the HI intensity distribution, which is emphasized by using only subtle colours for velocity.