The Extended Distribution of Baryons Around Galaxies
  We summarize and reanalyze observations bearing upon missing galactic
baryons, where we propose a consistent picture for halo gas in L >~ L*
galaxies. The hot X-ray emitting halos are detected to 50-70 kpc, where
typically, M_hot(<50 kpc) ~ 5E9 Msun, and with density n \propto r^-3/2. When
extrapolated to R200, the gas mass is comparable to the stellar mass, but about
half of the baryons are still missing from the hot phase. If extrapolated to
1.9-3 R200, the baryon to dark matter ratio approaches the cosmic value.
Significantly flatter density profiles are unlikely for R < 50 kpc and they are
disfavored but not ruled out for R > 50 kpc. For the Milky Way, the hot halo
metallicity lies in the range 0.3-1 solar for R < 50 kpc. Planck measurements
of the thermal Sunyaev-Zeldovich effect toward stacked luminous galaxies
(primarily early-type) indicate that most of their baryons are hot, near the
virial temperature, and extend beyond R200. This stacked SZ signal is nearly an
order of magnitude larger than that inferred from the X-ray observations of
individual (mostly spiral) galaxies with M_* > 10^11.3 Msun. This difference
suggests that the hot halo properties are distinct for early and late type
galaxies, possibly due to different evolutionary histories. For the cooler gas
detected in UV absorption line studies, we argue that there are two absorption
populations: extended halos; and disks extending to ~50 kpc, containing most of
this gas, and with masses a few times lower than the stellar masses. Such
extended disks are also seen in 21 cm HI observations and in simulations.
