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

¹ Department of Astronomy, University of Bologna, via Ranzani 1, 40127 Bologna, Italy
² Kapteyn Astronomical Institute, Postbus 800, 9700 AV Groningen, The Netherlands

^a e-mail: antonino.marasco2@unibo.it

Abstract

We modelled the distribution and the kinematics of HI in the inner Milky Way (R < R_☉) at latitude b = 0^∘ 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 H I 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.