HST WFPC-2 Imaging of Four Nearby LSB Galaxies

Abstract

Between May, 1996 and January, 1997 HST WFPC-2 images of four nearby LSB galaxies were taken through both the 8140Å and 3000Å filters. The first galaxy imaged, UGC 12695, is a nearby (z~0.021) LSB disk galaxy. UGC 12695 has an unusual morphology, consisting of a Y-shaped nucleus surrounded by a faint spiral arm. Additionally, numerous HI regions are spread throughout the galaxy. One of the surprising discoveries with the WFPC2 imaging was that a number of what were previously believed to be structural peculiarities in the galaxy are actually background galaxies. Once the effects of these galaxies are removed, the resultant U—I color of UGC 12695 is only −0.2, making it possibly the bluest galaxy in the local universe. When combined with the metallicity studies of McGaugh (1992), these colors indicate UGC 12695 to be a highly unevolved galaxy.

The other three galaxies imaged - V1L4, V2L8, and V7L3 - are dwarf elliptical galaxies located in the Virgo cluster. The intent of their images was to determine the galaxies’ small scale structure and place limits on the density and type of giant branch stars within each galaxy. Placed at the distance of the Virgo cluster, luminosity fluctuations indicate the galaxies to contain only from 4 – 13 stars per pixel, coinciding with a K/M giant ratio ranging from 6 to ∞ (no M giant stars). Additionally, we found no evidence for stellar clumping in these galaxies although an extremely red, extremely small bulge was found at the core of V2L8.