Galaxy Cluster Baryon Fractions Revisited
  We measure the baryons contained in both the stellar and hot gas components
for twelve galaxy clusters and groups at z~0.1 with M=1-5e14 Msun. This paper
improves upon our previous work through the addition of XMM data, enabling
measurements of the total mass and masses of each major baryonic component ---
ICM, intracluster stars, and stars in galaxies --- for each system. We recover
a relation for the stellar mass versus halo mass consistent with our previous
result. We confirm that the partitioning of baryons between the stellar and hot
gas components is a strong function of M500; the fractions of total mass in
stars and X-ray gas within r500 scale as M500^-0.45 and M500^0.26,
respectively. We also confirm that the combination of the BCG and intracluster
stars is an increasingly important contributor to the stellar baryon budget in
lower halo masses. We find a weak, but statistically significant, dependence of
the total baryon fraction upon halo mass, scaling as M500^0.16. For M500>2e14,
the total baryon fractions within r500 are on average 18% (7%) below the
Universal value from the WMAP7 (Planck) analysis. For Planck, the difference
between the Universal value and cluster baryon fractions is less than the
systematic uncertainties associated with M500. The total baryon fractions
exhibit significant scatter, particularly at M500<2e14 Msun where they range
from 60-90% (65-100%) of the Universal value for WMAP7 (Planck). The ratio of
the stellar-to-gas mass within r500, a measure of star formation efficiency,
strongly decreases with M500. The fact that this relation remains tight at low
mass implies that the larger scatter in the total baryon fractions at these
masses arises from either true scatter in the total baryon content or
observational scatter in M500, rather than late-time physical processes such as
redistribution of gas to beyond r500. (abridged)
