How axi-symmetric is the inner HI disc of the Milky Way?

TL;DR

This study models the distribution and motion of neutral hydrogen in the inner Milky Way, revealing that despite the galaxy's barred structure, the HI gas distribution is largely axi-symmetric.

Contribution

The paper introduces a new axi-symmetric model of the inner Milky Way's HI distribution and kinematics, fitted to 21-cm survey data using an iterative tangent-point method.

Findings

Model reproduces HI data well outside R<2 kpc

Inner region shows deviations, indicating non-axi-symmetry

Neutral gas distribution appears fairly axi-symmetric despite the barred potential

Abstract

We modelled the distribution and the kinematics of HI in the inner Milky Way (R<Rsun) at latitude b=0{\deg} assuming axi-symmetry. We fitted the line profiles of the LAB 21-cm survey using an iterative approach based on the tangent-point method. The resulting model reproduces the HI data remarkably well, with significant differences arising only for R<2 kpc. This suggests that, despite the presence of a barred potential, the neutral gas in the inner Milky Way is distributed in a fairly axi-symmetric disc.