Astrophysics Colloquium Constraining Progenitor Models and Cosmology with New Localizations of Fast Radio Bursts Presented by J. Xavier Prochaska University of California, Santa Cruz and University of California Observatories Thursday, October 3, 2019 11:00 A.M. in 169-336 and on Webex Abstract I will report on a set of new, well-localized (<1") fast radio bursts (FRBs) discovered by the ASKAP telescope. Nearly each of these events is coincident with a luminous galaxy which we designate as the host. The properties of these host galaxies and the spatial distribution of the FRBs within them rule out several classes of models proposed for FRBs. Spectra of the galaxies establish the FRB redshifts, offering a first assessment of the dispersion measure vs. redshift relation. This yields a new estimate of the cosmic baryon density for the low-z universe, consistent with measurements from BBN and the CMB, i.e. the so-called "missing" baryons have been found! Last, we analyze the rotation measure and pulse width of one FRB to study the magnetic field and density of gas in a foreground galaxy halo. JPL Contact: Joseph Lazio (4-4198)   Site Manager: Webmaster: CL 08-3220