Gas flow in barred potentials - III. Effects of varying the Quadrupole

TL;DR

This study uses hydrodynamical simulations to analyze how varying the quadrupole component of a galactic potential affects gas flow, aiding interpretation of Milky Way observations and constraining bar properties.

Contribution

It systematically investigates the impact of quadrupole variations on gas dynamics, providing constraints on the bar's scale length, strength, and pattern speed in the Milky Way.

Findings

Gas flow constrains the quadrupole and bar characteristics.

Bar's exponential scale length must be at least 1.5 kpc.

Pattern speed of the bar is favored at 40 km/s/kpc.

Abstract

We run hydrodynamical simulations of a 2D isothermal non self-gravitating inviscid gas flowing in a rigidly rotating externally imposed potential formed by only two components: a monopole and a quadrupole. We explore systematically the effects of varying the quadrupole while keeping fixed the monopole and discuss the consequences for the interpretation of longitude-velocity diagrams in the Milky Way. We find that the gas flow can constrain the quadrupole of the potential and the characteristics of the bar that generates it. The exponential scale length of the bar must be at least $1.5\rm\, kpc$. The strength of the bar is also constrained. Our global interpretation favours a pattern speed of $\Omega=40\,\rm km s^{-1} {kpc}^{-1}$. We find that for most observational features, there exist a value of the parameters that matches each individual feature well, but is difficult to reproduce all the important features at once. Due to the intractably high number of parameters involved in the general problem, quantitative fitting methods that can run automatic searches in parameter space are necessary.