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Galaxies are missing most of their baryons, and many models predict thesebaryons lie in a hot halo around galaxies. We establish observationallymotivated constraints on the mass and radii of these haloes using a variety ofindependent arguments. First, the observed dispersion measure of pulsars in theLarge Magellanic Cloud allows us to constrain the hot halo around the MilkyWay: if it obeys the standard NFW profile, it must contain less than 4-5% ofthe missing baryons from the Galaxy. This is similar to other upper limits onthe Galactic hot halo, such as the soft X-ray background and the pressurearound high velocity clouds. Second, we note that the X-ray surface brightnessof hot haloes with NFW profiles around large isolated galaxies is high enoughthat such emission should be observed, unless their haloes contain less than10-25% of their missing baryons. Third, we place constraints on the columndensity of hot haloes using nondetections of OVII absorption along AGNsightlines: in general they must contain less than 70% of the missing baryonsor extend to no more than 40 kpc. Flattening the density profile of galactichot haloes weakens the surface brightness constraint so that a typical L$_*$galaxy may hold half its missing baryons in its halo, but the OVII constraintremains unchanged, and around the Milky Way a flattened profile may only hold$6-13%$ of the missing baryons from the Galaxy ($2-4 \times 10^{10}M_{\odot}$). We also show that AGN and supernovae at low to moderate redshift -the theoretical sources of winds responsible for driving out the missingbaryons - do not produce the expected correlations with the baryonicTully-Fisher relationship and so are insufficient to explain the missingbaryons from galaxies. We conclude that most of missing baryons from galaxiesdo not lie in hot haloes around the galaxies, and that the missing baryonsnever fell into the potential wells of protogalaxies in the first place. Theymay have been expelled from the galaxies as part of the process of galaxyformation.

Do Hot Haloes Around Galaxies Contain the Missing Baryons?