Abstract
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). In addition, Lovelace and Richards (2013) showed
that DM could be measured even towards non-variable extragalactic synchrotron
sources. Motivated by these exciting results, 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.
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