Globular Cluster Systems and X-Ray Atmospheres in Galaxies

We compare the empirical relationships between the mass of a galaxy's globular cluster system (GCS) M-GCS, the gas mass in the hot X-ray atmosphere M-X within a fiducial radius of 5r(e), the total gravitational mass M-grav within 5r(e) and lastly the total halo mass M-h calibrated from weak lensing. We use a sample of 45 early-type galaxies for which both GCS and X-ray data are available; all the galaxies in our sample are relatively high-mass with M-h > 10(12) M-circle dot. We find that M-X alpha M-h(1.0), similar to the previously known scaling relation M-GCS proportional to M-h(1.0). Both components scale much more steeply than the more well known dependence of total stellar mass M* proportional to mu M-h(0.3) for luminous galaxies. These results strengthen previous suggestions that feedback had little effect on formation of the GCS. The current data are also used to measure the relative mass fractions of baryonic matter and dark matter within 5r(e). We find a strikingly uniform mean of a < f(DM)> = 0.83 with few outliers and an rms scatter of +/- 0.07. This result is in good agreement with two recent suites of hydrodynamic galaxy formation models.