A new technique to isolate kinematically anomalous gas in HI data cubes

TL;DR

This paper introduces a new decomposition method to identify and analyze kinematically anomalous HI gas in galaxies, revealing its dependence on star formation rate but not on environment, validated using cosmological simulations.

Contribution

The paper presents a simple, effective decomposition technique for isolating anomalous HI gas in galaxies, suitable for observational data and validated with simulations.

Findings

Anomalous gas fraction increases with specific star formation rate.

No significant dependence of anomalous gas on environmental density.

Method can be applied to future HI surveys.

Abstract

HI line observations of nearby galaxies often reveal the presence of extraplanar and/or kinematically anomalous gas that deviates from the general circular flow. In this work, we study the dependence of kinematically anomalous HI gas in galaxies taken from the Simba cosmological simulation on galaxy properties such as HI mass fraction, specific star formation rate, and local environmental density. To identify kinematically anomalous gas, we use a simple yet effective decomposition method to separate it from regularly-rotating gas in the galactic disk; this method is well-suited for application to observational datasets but has been validated here using the simulation. We find that at fixed atomic gas mass fraction, the anomalous gas fraction increases with the specific star formation rate. We also find that the anomalous gas fraction does not have a significant dependence on a galaxy's environment. Our decomposition method has the potential to yield useful insights from future HI surveys.