HI Deficiencies and Asymmetries in HIPASS Galaxies

TL;DR

This study analyzes the distribution of neutral hydrogen deficiency and spectral asymmetry in HIPASS galaxies, revealing environmental influences on HI deficiency but no clear link between asymmetry and deficiency.

Contribution

It introduces an updated binning statistic for measuring HI deficiency distribution and provides new insights into environmental effects on galaxy HI properties.

Findings

Galaxies in dense environments are more HI deficient.

No significant trend of spectral asymmetry with environment density.

HI asymmetry does not strongly depend on HI deficiency.

Abstract

We present an analysis of the sky distribution of neutral hydrogen (HI) deficiency and spectral asymmetry for galaxies detected by the HI Parkes All-Sky Survey (HIPASS) as a function of projected environment density. Previous studies of galaxy HI deficiency using HIPASS were sensitive to galaxies that are extremely HI rich or poor. We use an updated binning statistic for measuring the global sky distribution of HI deficiency that is sensitive to the average deficiencies. Our analysis confirms the result from previous studies that galaxies residing in denser environments, such as Virgo, are on average more HI deficient than galaxies at lower densities. However, many other individual groups and clusters are not found to be on average significantly HI poor, in contradiction to previous work. In terms of HI spectral asymmetries, we do not recover any significant trend of increasing asymmetry with environment density as found for other galaxy samples. We also investigate the correlation between HI asymmetry and deficiency, but find no variation in the mean asymmetry of galaxies that are HI rich, normal or poor. This indicates that there is either no dependence of asymmetry on HI deficiency, or a galaxy's HI deficiency only has a small influence on the measured HI asymmetry that we are unable to observe using only integrated spectra.