Fast Radio Burst Scattering Statistics through the Circumgalactic Medium Are Sensitive to Morphology and Intermittency
Year: 2026
Type: article
Abstract: The small-scale properties of circumgalactic gas in ordinary galaxies drive its bulk properties: the mass loading of cold neutral gas in galactic outflows affects their bulk momentum and gas cooling processes on small scales affect the spatial distribution of gas in the cool ( T ∼ 10 4 K) circumgalactic medium (CGM). However, hydrodynamical simulations have yet to resolve such small scales. Spectroscopy remains our primary probe of the small-scale CGM, with which subparsec scales are also challenging to resolve. Fast radio bursts (FRBs)—microsecond- to millisecond-duration radio pulses—are temporally broadened (“scattered”) by gradients in the electron density transverse to the line of sight, often generated by fluctuations on the smallest spatial scales. This makes FRB scattering a complementary and scalable probe of the small-scale CGM. We show that the distribution of scattering timescales induced by density fluctuations within a single, foreground halo—the “tau distribution function” (TDF)—is sensitive to the spatial morphology of the gas. The TDF is readily measurable and is analogous to areal covering factors reported in quasar absorption statistics. We compute the TDF in two regimes: scattering from a turbulent, volume-filling medium (“volumetric scattering”) and scattering from discrete structures localized along the line of sight (“intermittent scattering”). Within both of these regimes, the TDF is sensitive to whether the cool gas comprises spherical, filamentary (1D), or sheetlike (2D) structures. This work sets the stage for upcoming observations—from detectors like MeerKAT, Parkes, FAST, and the Deep Synoptic Array—which will use hundreds of sight lines through nearby halos to probe the small-scale CGM.
Source: The Astrophysical Journal
Authors: Dylan L. Jow, Calvin Leung
Institutions: Stanford University, University of California, Berkeley
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
OpenAlex ID: W7222927781