Evolution of the Blue Luminosity-to-Baryon Mass Ratio of Clusters of   Galaxies
  We derive the ratio of total blue luminosity to total baryon mass, LB/Mb, for massive (Mgas at the Abell radius is \ge 1 \times 10^{13} h^{-2.5} \Msolar) clusters of galaxies up to z \simeq 1 from the literature. Twenty-two clusters in our sample are at z > 0.1. Assuming that the relative mix of hot gas and galaxies in clusters does not change during cluster evolution, we use LB/Mb to probe the star formation history of the galaxy population as a whole in clusters. We find that LB/Mb of clusters increases with redshift from LB/Mb=0.024 (solar units) at z = 0 to \simeq 0.06 at z=1, indicating a factor of 2-3 brightening (we assume H0=70 km/s/Mpc). This amount of brightening is almost identical to the brightening of the M/LB ratio of early-type galaxies in clusters at 0.02 \le z \le 0.83 reported by van Dokkum et al. (1998). We compare the observed brightening of LB/Mb with luminosity evolution models for the galaxy population as a whole, changing the e-folding time of star formation \tau by 0.1 \le \tau \le 5 Gyr and the formation redshift \zF by 2 \le \zF < \infty. We find that \tau=0.1 Gyr 'single burst' models with \zF \ge 3 and \tau=5 Gyr 'disk' models with arbitrary \zF are consistent with the observed brightening, while models with \tau=1-2 Gyr tend to predict too steep brightening. We also derive the ratio of blue luminosity density to baryon density for field galaxies, adopting \Omega_b h^2 = 0.02, and find that blue luminosity per unit baryon is similar in clusters and in fields up to z \simeq 1 within the observational uncertainties. 
Kazuhiro Shimasaku (University of Tokyo)