Foreground Groups and Host-Galaxy Geometry in the Dispersion-Measure Scatter of Fast Radio Bursts
Abstract
Localized fast radio bursts (FRBs) show substantial scatter in dispersion measure (DM) about the mean cosmic DM--redshift relation, also known as the Macquart relation. Both foreground structure and host galaxies contribute to this scatter. In this work, we examine foreground tracers and host galaxy properties using a parent catalog of 136 localized FRBs with measured DMs and spectroscopic host redshifts. Among 77 FRBs within the Gfinder footprint, DM excess relative to a fixed Macquart mean increases with foreground group count excess, with a Spearman coefficient of 0.459. Adding the foreground term to a mean host baseline reduces the leave-one-out root mean square error (RMSE) and mean absolute error (MAE) in extragalactic DM by 13.0% and 7.5%, respectively. For 20 of these FRBs with optical host axis ratio measurements, adding a foreground term calibrated on the other 57 FRBs to the host shape model reduces the observer-frame leave-one-out RMSE from 76.3 to 64.0 pc cm−3 and MAE from 54.2 to 50.2 pc cm−3. And the in-sample residual standard deviation in the host rest frame decreases by 20.2%. Idealized galaxy models based on the Milky Way electron density distribution produce DM changes with inclination comparable to the fitted amplitude under the adopted assumptions.
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BibTeX
@misc{wang2026foreground,
title = {{Foreground Groups and Host-Galaxy Geometry in the Dispersion-Measure Scatter of Fast Radio Bursts}},
author = {Jiale Wang and Taotao Fang},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.23333},
eprint = {2610.23333},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.23333},
}
RIS
TY - UNPB
TI - Foreground Groups and Host-Galaxy Geometry in the Dispersion-Measure Scatter of Fast Radio Bursts
AU - Jiale Wang
AU - Taotao Fang
PY - 2026
DA - 2026/10/16
PB - arXiv
DO - 10.48550/arxiv.2610.23333
UR - https://arxiv.org/abs/2610.23333
AB - Localized fast radio bursts (FRBs) show substantial scatter in dispersion measure (DM) about the mean cosmic DM--redshift relation, also known as the Macquart relation. Both foreground structure and host galaxies contribute to this scatter. In this work, we examine foreground tracers and host galaxy properties using a parent catalog of 136 localized FRBs with measured DMs and spectroscopic host redshifts. Among 77 FRBs within the Gfinder footprint, DM excess relative to a fixed Macquart mean increases with foreground group count excess, with a Spearman coefficient of 0.459. Adding the foreground term to a mean host baseline reduces the leave-one-out root mean square error (RMSE) and mean absolute error (MAE) in extragalactic DM by 13.0% and 7.5%, respectively. For 20 of these FRBs with optical host axis ratio measurements, adding a foreground term calibrated on the other 57 FRBs to the host shape model reduces the observer-frame leave-one-out RMSE from 76.3 to 64.0 pc cm^−3 and MAE from 54.2 to 50.2 pc cm^−3. And the in-sample residual standard deviation in the host rest frame decreases by 20.2%. Idealized galaxy models based on the Milky Way electron density distribution produce DM changes with inclination comparable to the fitted amplitude under the adopted assumptions.
ER -