Halo Mass Estimation for Galaxy Groups: The Role Of Magnitude Gaps

We find that for the galaxy groups, the luminosity gap between the brightest and the subsequent brightest member galaxies in a halo (group) can be used to significantly reduce the scatter in the halo mass estimation based on the luminosity of the brightest galaxy alone. These corrections can significantly reduce the scatter in the halo mass estimations by ~ 50% to ~ 70% in massive halos.