Disentangling the Cosmic Web Towards FRB 190608
  FRB 190608 was detected by ASKAP and localized to a spiral galaxy at
$z_{host}=0.11778$ in the SDSS footprint. The burst has a large dispersion
measure ($DM_{FRB}=339.8$ $pc/cm^3$) compared to the expected cosmic average at
its redshift. It also has a large rotation measure ($RM_{FRB}=353$ $rad/m^2$)
and scattering timescale ($\tau=3.3$ $ms$ at $1.28$ $GHz$). Chittidi et al
(2020) perform a detailed analysis of the ultraviolet and optical emission of
the host galaxy and estimate the host DM contribution to be $110\pm 37$
$pc/cm^3$. This work complements theirs and reports the analysis of the optical
data of galaxies in the foreground of FRB 190608 to explore their contributions
to the FRB signal. Together, the two manuscripts delineate an observationally
driven, end-to-end study of matter distribution along an FRB sightline; the
first study of its kind. Combining KCWI observations and public SDSS data, we
estimate the expected cosmic dispersion measure $DM_{cosmic}$ along the
sightline to FRB 190608. We first estimate the contribution of hot, ionized gas
in intervening virialized halos ($DM_{halos} \approx 7-28$ $pc/cm^3$). Then,
using the Monte Carlo Physarum Machine (MCPM) methodology, we produce a 3D map
of ionized gas in cosmic web filaments and compute the DM contribution from
matter outside halos ($DM_{IGM} \approx 91-126$ $pc/cm^3$). This implies a
greater fraction of ionized gas along this sightline is extant outside
virialized halos. We also investigate whether the intervening halos can account
for the large FRB rotation measure and pulse width and conclude that it is
implausible. Both the pulse broadening and the large Faraday rotation likely
arise from the progenitor environment or the host galaxy.
