ABSTRACT

Simulations which explore mergers like those thought responsible for the shells around many elliptical galaxies find little correlation between the distribution of stars and gas in remnants. Mergers of small companion disks consisting of both gas and stars with non-spherical primary potentials produce shell galaxies with gaseous nuclear rings and clumps.

INTRODUCTION

Models which follow the infall of less-massive companion galaxies show that shell galaxies can be formed by accretion. However, it is probable that the sources of material also contain significant amounts of gas. We investigate encounters that produce shells by modeling interactions between non-spherical primary galaxies and companions containing both stars and gas with a three-dimensional code (TREESPH: Hernquist and Katz 1989). Primaries are modeled with rigid elliptical potentials of the form presented by Hernquist (1990) with scale-length a = 1. Physical time t′ is related to the calculation time unit by t′ ≈ 4.3 × 106t. The companion is a rotationally supported disk in which particles are distributed according to an exponential surface density profile. Stars have a total mass 1/10 and gas 1/100 that of the primary. In most interactions, the companion potential is disrupted at a small distance from the primary after which the particles evolve in the solitary primary gravitational field.