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 2 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 224 h _ { \mathrm { 70 } } ( M / L ) _ { \sun } in the rest frame B _ { \mathrm { 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 \propto L _ { \mathrm { B,j } } ^ { 1.08 \pm 0.12 } .
This implied lack of significant variation in star formation efficiency suggests that gas cooling can not 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 _ { \mathrm { 70 } } ^ { -3 / 2 } , which allows us to place an upper limit on the cosmological matter density , \Omega _ { \mathrm { m } } \leq 0.27 h _ { \mathrm { 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 .