Constraining the Cosmic Baryon Distribution with Fast Radio Burst
  Foreground Mapping
  The dispersion measures (DM) of fast radio bursts (FRBs) encode the
integrated electron density along the line-of-sight, which is typically
dominated by the intergalactic medium (IGM) contribution in the case of
extragalactic FRBs. In this paper, we show that incorporating wide-field
spectroscopic galaxy survey data in the foreground of localized FRBs can
significantly improve constraints on the partition of diffuse cosmic baryons.
Using mock DMs and realistic lightcone galaxy catalogs derived from the
Millennium simulation, we define spectroscopic surveys that can be carried out
with 4m and 8m-class wide field spectroscopic facilities. On these simulated
surveys, we carry out Bayesian density reconstructions in order to estimate the
foreground matter density field. In comparison with the `true' matter density
field, we show that these can help reduce the uncertainties in the foreground
structures by $\sim 2-3\times$ compared to cosmic variance. We calculate the
Fisher matrix to forecast that $N=30\: (96)$ localized FRBs should be able to
constrain the diffuse cosmic baryon fraction to $\sim 10\%\: (\sim 5\%) $, and
parameters governing the size and baryon fraction of galaxy circumgalactic
halos to within $\sim 20-25\%\: (\sim 8-12\%)$. From the Fisher analysis, we
show that the foreground data increases the sensitivity of localized FRBs
toward our parameters of interest by $\sim 25\times$. We briefly introduce
FLIMFLAM, an ongoing galaxy redshift survey that aims to obtain foreground data
on $\sim 30$ localized FRB fields.
