The Shape of Dark Matter Haloes II. The Galactus HI Modelling & Fitting Tool

TL;DR

The paper introduces extsc{Galactus}, a new tool for modeling and fitting HI data in disc galaxies, accounting for self-absorption effects, and demonstrates its application on NGC2403, revealing significant self-absorption impacts.

Contribution

The paper presents extsc{Galactus}, a publicly available software that automates HI galaxy modeling with self-absorption treatment, advancing analysis accuracy.

Findings

Self-absorption occurs even in face-on galaxies.

Maximum surface brightness plateaus indicate self-absorption.

Edge-on HI mass appears lower due to self-absorption.

Abstract

We present a new HI modelling tool called \textsc{Galactus}. The program has been designed to perform automated fits of disc-galaxy models to observations. It includes a treatment for the self-absorption of the gas. The software has been released into the public domain. We describe the design philosophy and inner workings of the program. After this, we model the face-on galaxy NGC2403, using both self-absorption and optically thin models, showing that self-absorption occurs even in face-on galaxies. It is shown that the maximum surface brightness plateaus seen in Paper I of this series are indeed signs of self-absorption. The apparent HI mass of an edge-on galaxy can be drastically lower compared to that same galaxy seen face-on. The Tully-Fisher relation is found to be relatively free from self-absorption issues.