  Most of the baryons in L* galaxies are unaccounted for and are predicted to
lie in hot gaseous halos (T ~ 3E6 K) that may extend beyond R200. A hot gaseous
halo will produce a thermal Sunyaev-Zeldovich signal that is proportional to
the product of the gas mass and the mass-weighted temperature. To best detect
this signal, we used a Needlet Independent Linear Combination all-sky Planck
map that we produced from the most recent Planck data release, also
incorporating WMAP data. The sample is 12 L* spiral galaxies with distances of
3-10 Mpc, which are spatially resolved so that contamination from the optical
galaxy can be excluded. One galaxy, NGC 891, has a particularly strong SZ
signal, and when excluding it, the stack of 11 galaxies is detected at about
4sigma (declining with radius) and is extended to at least 250 kpc (~R_{200})
at > 99% confidence. The gas mass within a spherical volume to a radius of 250
kpc is 9.8 +/- 2.8 E10 Msun, for Tavg = 3E6 K. This is about 30% of the cosmic
baryon content of the average galaxy (3.1E11 Msun), and about equal to the mass
of stars, disk gas, and warm halo gas. The remaining missing baryons (~ 1.4E11
Msun, 40-50% of the total baryon content) are likely to be hot and extend to
the 400-500 kpc volume, if not beyond. The result is higher than predictions,
but within the uncertainties.
