Mass‐to‐Light Ratios of Galaxy Groups from Weak Lensing

We present the findings of our weak lensing study of a sample of 116 CNOC2galaxy groups. The lensing signal is used to estimate the mass-to-light ratioof these galaxy groups. The best fit isothermal sphere model to our lensingdata has an Einstein radius of 0.88"+/-0.12", which corresponds to ashear-weighted velocity dispersion of 245+/-18 km/s. The mean mass-to-lightratio within 1 h^-1 Mpc is 185+/-28 h times solar in the B-band and isindependent of radius from the group center. The signal-to-noise ratio of the shear measurement is sufficient to split thesample into subsets of "poor" and "rich" galaxy groups. The poor galaxy groupswere found to have an average velocity dispersion of 193+/-38 km/s and amass-to-light ratio of 134+/-26 h times solar in the B-band, while the richgalaxy groups have a velocity dispersion of 270+/-39 km/s and a mass-to-lightratio of 278+/-42 h times solar in the B-band, similar to the mass-to-lightratio of clusters. This steep increase in the mass-to-light ratio as a functionof mass, suggests that the mass scale of ~10^13 solar masses is where thetransition between the actively star-forming field environment and thepassively-evolving cluster environment occurs. This is the first such detectionfrom weak lensing.Comment: Accepted for publication in ApJ 6 pages, 6 figures, uses emulateap