ABSTRACT

In this paper I briefly review the flow of gas in and around the bars of early type, strongly barred galaxies. I discuss the formation and location of the shocks near the leading edges of bars and the parameters that influence them. Straight shock loci can also be loci of such high shear that no stars can form there, although they correspond to important density enhancements. The flows found in barred galaxies entail a considerable amount of inflow. If inner Lindblad resonances are absent, or if one or more secondary bars exist within the primary one, then this inflowing gas can come very near to the galactic center.

INTRODUCTION

Modelling the interstellar medium in order to follow the gas flow in and around bars is not a straightforward matter. Two families of approaches have been developed so far for that purpose:

1. Codes treating the cool dense clouds as ballistic particles with a finite cross section, often called “sticky particle” codes. Exactly when two such clouds are considered to collide and what happens in such a case varies from one code to the other (Taff and Savedoff 1972; Larson 1978; Schwarz 1979).

2. Codes considering a collection of these clouds as a fluid with a sound speed of the order of the velocity dispersion of the clouds, i.e. of the order of 5 to 10 km sec-1 (cf. Cowie 1980). This group of codes is composed of at least three subgroups:

1. i) Difference schemes, in which several different ways of solving the hydrodynamic equations are used (see e.g. Prendergast 1983 and references therein).

2. ii) the beam scheme (Sanders and Prendergast 1974).

3. […]