The Birmingham-CfA cluster scaling project - II. Mass composition and distribution

We investigate the spatial distribution of the baryonic and non-baryonic mass components in a sample of 66 virialized systems. We have used X-ray measurements to determine the deprojected temperature and density structure of the intergalactic medium and have employed these to map the underlying gravitational potential. In addition, we have measured the deprojected spatial distribution of galaxy luminosity for a subset of this sample, spanning over two decades in mass. With this combined X-ray/optical study, we examine the scaling properties of the baryons and address the issue of mass-to-light (M/L) ratio in groups and clusters of galaxies. We measure a median mass-to-light ratio of 249 h(70)(M/L)(.) in the rest frame B-J band, in good agreement with other measurements based on X-ray determined masses. There is no trend in M/L with X-ray temperature and no significant trend for mass to increase faster than luminosity: M proportional to L-BJ(1.08+/-0.12). This implied lack of significant variation in star formation efficiency suggests that gas cooling cannot be greatly enhanced in groups, unless it drops out to form baryonic dark matter. Correspondingly, our results indicate that non-gravitational heating must have played a significant role in establishing the observed departure from self-similarity in low-mass systems. The median baryon fraction for our sample is 0.162 h(70)(-3/2), which allows us to place an upper limit on the cosmological matter density, Omega(m) less than or equal to 0.27 h(70)(-1), in good agreement with the latest results from WMAP. We find evidence of a systematic trend towards higher central density concentration in the coolest haloes, indicative of an early formation epoch and consistent with hierarchical formation models.