Gas flow in barred potentials

TL;DR

This study simulates gas flow in a barred galaxy potential, examining how sound speed and grid resolution influence shock formation, orbit shifts, and flow stability, with implications for observed galactic asymmetries.

Contribution

It demonstrates how varying sound speed and resolution affect shock locations and flow stability, supporting the hypothesis that flow transitions occur at the cusped orbit.

Findings

Shocks and orbit shifts depend strongly on sound speed and resolution.

Flow downstream of shocks becomes unsteady at high resolutions.

Unsteady flow may explain observed asymmetries in CO distribution.

Abstract

We use a Cartesian grid to simulate the flow of gas in a barred Galactic potential and investigate the effects of varying the sound speed in the gas and the resolution of the grid. For all sound speeds and resolutions, streamlines closely follow closed orbits at large and small radii. At intermediate radii shocks arise and the streamlines shift between two families of closed orbits. The point at which the shocks appear and the streamlines shift between orbit families depends strongly on sound speed and resolution. For sufficiently large values of these two parameters, the transfer happens at the cusped orbit as hypothesised by Binney et al. over two decades ago. For sufficiently high resolutions the flow downstream of the shocks becomes unsteady. If this unsteadiness is physical, as appears to be the case, it provides a promising explanation for the asymmetry in the observed distribution of CO.