Mass-to-Light Ratios of 2dF Galaxies

We compute M , the dynamical mass interior to a radius of 260 h -1 kpc, for a set of 809 isolated host galaxies in the 100k data release of the 2dF Galaxy Redshift Survey. The hosts are surrounded by 1556 fainter satellite galaxies. Our mass estimator and host/satellite selection criteria are taken from those used by the Sloan Digital Sky Survey collaboration for a similar analysis of M , and overall our results compare well with theirs. In particular, for L ≳ 2 L *, we find ( M / L ) = 193 ± 14 h M ☉ / L ☉ , with a weak tendency for hosts with L < 2 L * to have a somewhat higher M / L . Additionally, we investigate M / L for bright ( b J ≲ 18) galaxies with elliptical, S0, and spiral morphologies. There are 159 hosts in the elliptical/S0 sample; similar to the full sample, ( M / L ) = 271 ± 26 h M ☉ / L ☉ for galaxies with L ≳ 2 L *. There is a weak tendency for less luminous galaxies to have a somewhat higher M / L . In stark contrast to this, the line-of-sight velocity dispersion for the 243 spiral hosts is independent of the host luminosity, with a value of σ v = 189 ± 19 km s -1 . Thus, for spiral hosts, we find ( M / L ) ∝ L -1.0±0.2 , where ( M / L ) for a 2 L * spiral galaxy is of order 200 h M ☉ / L ☉ .