ABSTRACT

On scales larger than 1 Mpc, Low Surface Brightness (LSB) galaxies are found in the same environment as the general population of disk galaxies. However, in a region of phase space defined by projected radius 0.5 Mpc and relative velocity = 500 km s-1, LSB galaxies are extremely isolated. In addition, the average distance to a nearby galaxy of comparable mass is 1.7 times farther for LSB galaxies than for conventional disks. Since it is this small scale environment which determines the frequency of tidal interactions, the data argue that LSBs have not experienced a mass transfer event in the last Hubble time. The lack of such interactions clearly give these disks a different star formation history than their high surface brightness brethren and further implies that mean galactic surface brightness is a function of small-scale environment. To add further complexity, we have also identified a particular class of large-scale length LSB galaxy that, although isolated, invariably hosts a Seyfert 1 nucleus.

INTRODUCTION

Most conferences on topics in extragalactic astronomy are an entertaining mixture of apparent observational data which gives rise to theoretical conjecture followed by rampant folklore, wishful thinking and/or just plain rejection of the data as being relevant. This allows most theories to remain relatively unconstrained. For instance, the role that environment plays in the evolution of galaxies remains a contentious issue. To be sure, the present arrangement of galaxies into clusters, low density but large scale walls, or shells surrounding large scale voids means that a wide range of environments do exist.