Dynamics of Gas in Major Mergers (Invited paper)

Summary

ABSTRACT

Possible consequences of the dynamics of interstellar gas in merging galaxies are discussed and illustrated with numerical simulations which incorporate both collisionless and hydrbdynamical evolution.

INTRODUCTION

Over the past 20 years, considerable observational evidence has accumulated implying that “major” mergers of comparable–mass spirals may play an important role in the evolution of galaxies. Based on statistics on well–known merger candidates, Toomre and Toomre (1972) and later Toomre (1977) argued that major mergers are the dominant process by which early–type galaxies form. More recently, infrared and radio surveys have bolstered long–standing suspicions that nuclear starbursts in some peculiar objects may have been triggered by mergers of gas–rich progenitors [e.g. Sanders et al. 1988a, b; Sanders 1992). Only slightly less compelling are observations implicating galaxy collisions to the onset of activity in bright radio galaxies (e.g. Heckman et al. 1986) and quasars (e.g. Stockton 1990). (For a review, see Barnes and Hernquist 1992a.)

By now, the stellar–dynamics of major mergers have been explored in some detail using N-body simulation (e.g. Barnes 1988, 1992; Hernquist 1992, 1993a); however studies of the hydrodynamical evolution of interstellar gas during these events are less fully developed. Seminal works include simplified calculations, which ignore self–consistency, showing that bars in disks can drive nuclear inflows of gas (Simkin et al. 1980), low–resolution models investigating the fate of a dissipative component during major mergers (Negroponte and White 1983), simulations of gas inflow during transient collisions between galaxies (e.g. Noguchi 1988, 1991; Combes et al. 1990), and possible consequences of star formation and feedback (e.g. Mihos et al. 1991, 1992).