WALLABY Early Science - I. The NGC 7162 Galaxy Group

TL;DR

This paper presents early science results from ASKAP's WALLABY survey of the NGC 7162 galaxy group, detecting new HI-rich galaxies, confirming extended HI emission, and analyzing galaxy dynamics with high-resolution data.

Contribution

First application of ASKAP WALLABY data to the NGC 7162 group, expanding group membership, detecting new HI-rich dwarf galaxies, and analyzing their dynamics with improved resolution.

Findings

Detected six galaxies in HI, increasing known group members from four to seven.

First HI detections of two dwarf galaxies, with measured velocities.

Confirmed extended HI emission around NGC 7162, indicating past interactions.

Abstract

We present Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY) early science results from the Australian Square Kilometre Array Pathfinder (ASKAP) observations of the NGC 7162 galaxy group. We use archival HIPASS and Australia Telescope Compact Array (ATCA) observations of this group to validate the new ASKAP data and the data reduction pipeline ASKAPsoft. We detect six galaxies in the neutral hydrogen (HI) 21-cm line, expanding the NGC 7162 group membership from four to seven galaxies. Two of the new detections are also the first HI detections of the dwarf galaxies, AM 2159-434 and GALEXASC J220338.65-431128.7, for which we have measured velocities of $cz=2558$ and $cz=2727$ km s$^{-1}$, respectively. We confirm that there is extended HI emission around NGC 7162 possibly due to past interactions in the group as indicated by the $40^{\circ}$ offset between the kinematic and morphological major axes for NGC 7162A, and its HI richness. Taking advantage of the increased resolution (factor of $\sim1.5$) of the ASKAP data over archival ATCA observations, we fit a tilted ring model and use envelope tracing to determine the galaxies' rotation curves. Using these we estimate the dynamical masses and find, as expected, high dark matter fractions of $f_{\mathrm{DM}}\sim0.81-0.95$ for all group members. The ASKAP data are publicly available.