The dark matter halo shape of edge-on disk galaxies - II. Modelling the HI observations: methods

TL;DR

This paper develops and tests improved methods for analyzing HI observations in edge-on galaxies to better constrain dark matter halo shapes by accurately measuring gas kinematics and distribution.

Contribution

It introduces an extended radial decomposition XV modelling method that accounts for variable HI velocity dispersion and evaluates its effectiveness.

Findings

Extended the constant velocity dispersion method to include radial variation.

Performed extensive tests demonstrating the method's accuracy and limitations.

Prepared for application to a sample of 8 galaxies in subsequent work.

Abstract

This is the second paper of a series in which we attempt to put constraints on the flattening of dark halos in disk galaxies. For this purpose, we observe the HI in edge-on galaxies, where it is in principle possible to measure the force field in the halo vertically and radially from gas layer flaring and rotation curve decomposition respectively. To calculate the force fields, we need to analyse the observed XV diagrams to accurately measure all three functions that describe the planar kinematics and distribution of a galaxy: the radial HI surface density, the rotation curve and the HI velocity dispersion. In this paper, we discuss the improvements and limitations of the methods previously used to measure these HI properties. We extend the constant velocity dispersion method to include determination of the HI velocity dispersion as a function of galactocentric radius and perform extensive tests on the quality of the fits. We will apply this 'radial decomposition XV modelling method' to our HI observations of 8 HI-rich, late-type, edge-on galaxies in the third paper of this series.