A high excitation HII region in the faint dwarf elliptical galaxy A0951+68

Abstract

We present the results of BVRI imaging and optical spectroscopy of the dwarf galaxy A0951+68. The images reveal that, although this galaxy is classified as a dwarf elliptical, it has some properties that are similar to dwarf irregular galaxies. It contains two bright knots of emission, one of which is red and unresolved and the other blue and resolved. The blue knot also shows a high excitation emission line spectrum. The observed line ratios indicate that this is an HII region, although with some line ratios that are border-line with those in AGN. The emission line luminosity is consistent with ionisation by a single, very luminous O star, or several smaller O stars, but the extended blue light in the knot shows that this has occurred as part of a substantial recent star formation event. We find that the metal abundance, while low compared to typical large galaxies, actually seems to be high for such a low luminosity dwarf. The position of A0951 in the literature is incorrect and we provide the correct value.