ASKAP HI imaging of the galaxy group IC 1459

TL;DR

This study uses ASKAP HI imaging to detect and analyze gas clouds in the IC 1459 galaxy group, revealing significant intra-group gas and gas exchange processes with no clear stellar counterparts.

Contribution

First detailed HI imaging of the IC 1459 group with discovery of gas clouds and evidence of extensive intra-group gas, highlighting gas exchange in galaxy evolution.

Findings

Detected 11 galaxies with HI down to 10^20 cm^-2

Discovered three HI clouds with 10^9 M_sun each

Found intra-group HI mass exceeds that within galaxies by over 10%

Abstract

We present HI imaging of the galaxy group IC 1459 carried out with six antennas of the Australian SKA Pathfinder equipped with phased-array feeds. We detect and resolve HI in eleven galaxies down to a column density of $\sim10^{20}$ cm$^{-2}$ inside a ~6 deg$^2$ field and with a resolution of ~1 arcmin on the sky and ~8 km/s in velocity. We present HI images, velocity fields and integrated spectra of all detections, and highlight the discovery of three HI clouds -- two in the proximity of the galaxy IC 5270 and one close to NGC 7418. Each cloud has an HI mass of $10^9$ M$_\odot$ and accounts for ~15% of the HI associated with its host galaxy. Available images at ultraviolet, optical and infrared wavelengths do not reveal any clear stellar counterpart of any of the clouds, suggesting that they are not gas-rich dwarf neighbours of IC 5270 and NGC 7418. Using Parkes data we find evidence of additional extended, low-column-density HI emission around IC 5270, indicating that the clouds are the tip of the iceberg of a larger system of gas surrounding this galaxy. This result adds to the body of evidence on the presence of intra-group gas within the IC 1459 group. Altogether, the HI found outside galaxies in this group amounts to several times $10^9$ M$_\odot$, at least 10% of the HI contained inside galaxies. This suggests a substantial flow of gas in and out of galaxies during the several billion years of the group's evolution.