The V_c- sigma_c relation in high and low surface brightness galaxies

We investigate the relation between the asymptotic circular velocity, V_c , and the central stellar velocity dispersion, sigma_c , in galaxies. We consider a new sample of high surface brightness spiral galaxies (HSB), low surface brightness spiral galaxies (LSB), and elliptical galaxies with H I-based V_c measurements. We find that: 1) elliptical galaxies with H I measurements fit well within the relation; 2) a linear law can reproduce the data as well as a power law (used in previous works) even for galaxies with sigma_c < 70 km/s; 3) LSB galaxies, considered for the first time with this respect, seem to behave differently, showing either larger V_c values or smaller sigma_c values. If the V_c-sigma_c relation is equivalent to one between the mass of the dark matter halo and that of the supermassive black hole, these results suggest that the LSB galaxies host a supermassive black hole with a smaller mass compared to HSB galaxies of equal dark matter halo. On the other hand, if the fundamental correlation of SMBH mass is with the halo circular velocity, then LSBs should have larger black hole masses for given bulge dispersion.