RAM PRESSURE STRIPPING OF THE LARGE MAGELLANIC CLOUD'S DISK AS A PROBE OF THE MILKY WAY'S CIRCUMGALACTIC MEDIUM

Recent observations have constrained the orbit and structure of the Large Magellanic Cloud (LMC), implying a well-constrained pericentric passage about the Milky Way (MW) similar to 50 Myr ago. In this scenario, the LMC's gaseous disk has recently experienced stripping, suggesting the extent of its H-I disk directly probes the medium in which it is moving. From the observed stellar and H-I distributions of the system we find evidence of a truncated gas profile along the windward leading edge of the LMC disk, despite a far more extended stellar component. We explore the implications of this ram pressure stripping signature, using both analytic prescriptions and full three-dimensional hydrodynamic simulations of the LMC. Our simulations can match the radial extent of the LMC's leading (windward) edge only in scenarios where the MW CGM density at pericentric passage is n(p) (R = 48.2 +/- 5 kpc) = 1.1(-.45)(+.44) x 10(-4) cm(-3). The implied pericentric density proves to be insensitive to both the broader CGM and temperature profiles, thus providing a model-independent constraint on the local gas density. This result imposes an important constraint on the density profile of the MW's CGM at 50 kpc, and thus also on the total baryon content of the MW. From our work, assuming a beta-profile valid to similar to r(vir), we infer a total diffuse CGM mass M (300 kpc) = 2.7. +/- 1.4 x 10(10)M(circle dot) or approximately 15% of a 10(12)M(circle dot) MW's baryonic mass budget.