The Local Origin of a Host Dispersion Measure-Stellar Mass Relation in Fast Radio Bursts

Abstract

The origin of fast radio bursts (FRBs) and the relationship to their host galaxy environments remain open questions. Using a sample of 37 FRBs with secure host associations at $z\lesssim 0.25$, and including dwarf, elliptical, and edge-on hosts, we examine the host dispersion measure ($\mathrm{D}{\mathrm{M}}_{\mathrm{host}}$) and its dependence on host stellar mass ($M_{\star }$). We find a statistically significant anti-correlation between the host dispersion measure and host stellar mass (the $\mathrm{D}{\mathrm{M}}_{\mathrm{host}}$-$M_{\star }$ relation; Pearson $r\approx -0.5$, ${\log }_{10}p\approx -2.8$) that extends across the full range of our sample, ${\log }_{10}(M_{\star }/M_{\odot })\approx 8$-$11.4$. We find that the rest-frame Faraday rotation measure ($|\mathrm{RM}{|}_{\mathrm{host}}$) is largest in FRBs that reside in dwarf galaxies, but there is no evidence for a correlation across the full mass range. We show that the $\mathrm{D}{\mathrm{M}}_{\mathrm{host}}$-$M_{\star }$ trend does not arise from the galaxy-averaged interstellar medium (ISM) nor from the circumgalactic medium (CGM). Instead, we argue that the local ($\lesssim 100$ pc) environment is responsible. The spatial statistics of star formation and metallicity-dependent FRB progenitor channels plausibly lead to denser ionized environments in low-mass galaxies and less nearby gas in massive hosts.

17 pages, 4 figures, submitted to ApJ