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 ) . \citet chittidi+20 perform a detailed analysis of the ultraviolet and optical emission of the host galaxy and estimate the host DM contribution to be 137 \pm 43 ~ { } { 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 .