Mapping the cosmic web along FRB sightlines

Sunil Simha
UC Santa Cruz
Tuesday, October 3, 2023
4:00 pm
NS2 1201


Fast radio bursts (FRBs) are among the newest tools in observational astrophysicists’ repertoire to study ionized gas. Their unique, millisecond-duration radio signal is subject to propagation effects in the intervening plasma. One such effect is the plasma dispersion of FRB pulses. FRB dispersion measures (DMs) quantify the net free electron column density through the sightline. FRB DMs can be precisely measured (~0.1%) and thus are sensitive to the most diffuse plasma in the intergalactic medium (IGM) that traditional probes have found challenging to illuminate. This ability to provide novel constraints on plasma has motivated studies of the circumgalactic medium (CGM) of galaxies intersecting FRB sightlines and the cosmic web filaments of the IGM. In my talk, I will highlight some of the work already done leveraging FRBs and introduce the FLIMFLAM survey. The survey is an ongoing endeavor to map foreground matter density along ~20 FRB sightlines. To this end, the survey measures spectroscopic redshifts of the foreground galaxies. Its ultimate aim is to produce statistical constraints on key parameters describing matter distribution in the universe, including the fractions of ionized baryons residing in the diffuse IGM and the virialized gas of halos. We expect our first data release by the end of 2023. Meanwhile, some of our recent work focuses on interesting sightlines that exhibit unusually large DMs. Through foreground mapping, we confirm large host galaxy DMs in some sightlines while others show numerous foreground structures. I will also discuss one sightline where foreground mapping revealed cluster gas that enhanced the DM. I will end with prospects for FRB-based analyses that excite me.

Paul Robertson