The νc-σc relation in low-mass and low surface brightness galaxies

We present an updated investigation of the relation between large-scale disc circular velocity, v(c), and bulge velocity dispersion, sigma(c). New bulge velocity dispersions are measured for a sample of 11 low surface brightness (LSB) and seven high surface brightness (HSB) spiral galaxies for which v(c) is known from published optical or H I rotation curves. We find that, while LSB galaxies appear to define the upper envelope of the region occupied by HSB galaxies (having relatively larger v(c) for any given sigma(c)), the distinction between LSB and HSB galaxies in the v(c)-sigma(c) plane becomes less pronounced for sigma(c) less than or similar to 80 km s(-1). We conclude that either the scatter of the v(c)-sigma(c) relation is a function of v(c) (and hence galaxy mass) or the character of the v(c)-sigma(c) relation changes at v(c) similar to 80 km s(-1). Some implications of our findings are discussed.