Fast Radio Burst Scattering Statistics through the Circumgalactic Medium Are Sensitive to Morphology and Intermittency
- 1Stanford University
- 2University of California Berkeley
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.
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BibTeX
@article{jow2026fast,
title = {{Fast Radio Burst Scattering Statistics through the Circumgalactic Medium Are Sensitive to Morphology and Intermittency}},
author = {Dylan L. Jow and Calvin Leung},
journal = {The Astrophysical Journal},
year = {2026},
month = oct,
doi = {10.3847/1538-4357/aea6db},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea6db},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Fast Radio Burst Scattering Statistics through the Circumgalactic Medium Are Sensitive to Morphology and Intermittency
AU - Dylan L. Jow
AU - Calvin Leung
PY - 2026
DA - 2026/10/19
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/aea6db
UR - https://iopscience.iop.org/article/10.3847/1538-4357/aea6db
AB - 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.
SN - 0004-637X
SN - 1538-4357
ER -