Collaborative Research: Disentangling the Cosmic Web with Fast Radio Bursts

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For many years, astronomers have been trying to understand and observe the diffuse gas between galaxies, also known as the intergalactic medium (IGM) or -- more colloquially -- the cosmic web. A research collaboration between the University of California-Santa Cruz (UCSC) and the Maria Mitchell Observatory (MMO) will use precise observations of a recently discovered type of short astronomical event called fast radio bursts (FRBs) to investigate and attempt to disentangle the cosmic web. This project will involve the acquisition and analysis of optical and infrared follow-up observations of over 100 well-localized FRBs, discovered using the leading FRB experiments for precise localization (ASKAP, realfast, and DSA-110) and then observed with large aperture telescopes. Using the planned dataset, the astronomers will focus on three main activities: (i) obtain follow-up imaging and spectroscopy of the galaxies hosting FRBs, (ii) resolve the distribution of ionized gas in the Local Group of galaxies, and (iii) disentangle the cosmic web. The project will support the education and training of a full-time PhD student at UCSC in observational astronomy. The Bridge program at MMO, meanwhile, will provide postgraduate students from underrepresented communities the opportunity to build the skill set (e.g. programming, statistics, observing) needed to transition into a PhD program. Numerical simulations on cosmological scales (~100 Mpc) now purport to capture all of the salient physics required to accurately predict the astrophysics of the IGM. These simulations predict that about 50% of the gas is in a warm-hot ionized medium (WHIM), shock-heated during its collapse onto large-scale structures. Despite several decades of observational searches for the WHIM, however, it remains the most elusive baryonic reservoir of the universe. Meanwhile, on the scales of individual dark matter halos (~100 -- 1000 kpc), theorists debate on the mass and distribution of gas within them. The program will leverage a new opportunity to disentangle the cosmic web through a comprehensive, observational survey of FRB events. The three main research areas arising from the three observational activities listed above are: (i) establish the FRB redshift and provide new insights into the progenitors that generate these enigmatic phenomena; (ii) use the observed FRB dispersion measures to perform a series of experiments designed to survey the halo gas of our Galaxy and M31, while also searching for the putative Local Group medium; and (iii) directly test the modern paradigm for the IGM (and its WHIM) and assess the baryon fraction of dark matter halos as a function of their mass, morphology, and environment. To support the great breadth of science derived from FRB observations beyond the focus of the project, all of the data obtained with this program will be disseminated to the community through one or more channels.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.