Locating the "missing" baryons with extragalactic dispersion measure
  estimates
  Recently, Thornton and coworkers (2013) confirmed a class of millisecond
radio bursts likely of extragalactic origin that is well-suited for estimating
dispersion measures (DMs). We calculate the probability distribution of DM(z)
in different models for how the cosmic baryons are distributed (both
analytically and with cosmological simulations). We show that the distribution
of DM is quite sensitive to whether the "missing" baryons lie around the virial
radius of 10^11-10^13 Msun halos or further out, which is not easily
constrained with other observational techniques. The intrinsic contribution to
DM from each source could complicate studies of the extragalactic contribution.
This difficulty is avoided by stacking based on the impact parameter to
foreground galaxies. We show that a stacking analysis using a sample of ~100 DM
measurements from arcminute-localized, z >~ 0.5 sources would place interesting
constraints at 0.2-2 halo virial radii on the baryonic mass profile surrounding
different galaxy types. Conveniently for intergalactic studies, sightlines that
intersect intervening galactic disks should be easily identified owing to
scattering. A detectable level of scattering may also result from turbulence in
the circumgalactic medium.
