neutral hydrogen

Monthly Notices of the Royal Astronomical Society

The precise localization (&lt;1'') of multiple fast radio bursts (FRBs) to z&gt;0.1\ngalaxies has confirmed that the dispersion measures (DMs) of these enigmatic\nsources afford a new opportunity to probe the diffuse ionized gas around and in\nbetween galaxies. In this manuscript, we examine the signatures of gas in dark\nmatter halos (aka halo gas) on DM observations in current and forthcoming FRB\nsurveys. Combining constraints from observations of the high velocity clouds,\nOVII absorption, and the DM to the Large Magellanic Cloud with hydrostatic\nmodels of halo gas, we estimate that our Galactic halo will contribute ${\\rm\nDM}_{\\rm MW,halo} \\approx 50-80 \\rm pc/cm^{-3}$ from the Sun to 200 kpc\nindependent of any contribution from the Galactic ISM. Extending analysis to\nthe Local Group, we demonstrate that M31's halo will be easily detected by\nhigh-sample FRB surveys (e.g. CHIME) although signatures from a putative Local\nGroup medium may compete. We then review current empirical constraints on halo\ngas in distant galaxies and discuss the implications for their DM\ncontributions. We further examine the DM probability distribution function of a\npopulation of FRBs at z &gt;&gt; 0 using an updated halo mass function and new models\nfor the halo density profile. Lastly, we illustrate the potential of FRB\nexperiments for resolving the baryonic fraction of halos by analyzing simulated\nsightlines through the CASBaH survey. All of the code and data products of our\nanalysis are available at https://github.com/FRBs.\n

Probing Galactic Halos with Fast Radio Bursts