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From Dispersion to Metallicity: Probing the Milky Way Circumgalactic Medium with Fast Radio Bursts

  • Manami Roy
  • Sanskriti Das
  • Smita Mathur
  • Anjali Gupta
  • Yair Krongold
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Abstract

Circumgalactic Medium (CGM) plays a critical role in galactic evolution, serving as the primary reservoir for accretion and outflows. In this work, we present a novel statistical analysis to derive CGM metallicity from the dispersion measure (DM) of 25 Fast Radio Burst (FRB) sightlines. By combining metallicity-dependent oxygen absorption DM estimates with metallicity-independent FRB DMs, we directly constrain the metallicity of the hot phase of the Milky Way (MW) CGM. Considering different diffuse baryon fractions (fd = 0.0, 0.6, 0.8) in the Intergalactic Medium (IGM) and intervening halos, the median metallicities of CGM are ZCGM = 0.12−0.04+0.09 Z⊙, 0.26−0.12+0.18 Z⊙, and 0.39−0.20+0.26 Z⊙, respectively, by the bootstrapping method. Super-solar metallicity is seen in multiple sightlines for fd=0.8, which is implausible for MW CGM metallicities. Even under conservative lower-bound estimates (fd = 0.0), the inferred CGM metallicity significantly exceeds expectations for IGM accretion (ZIGM ≲ 0.1 Z⊙), providing strong empirical evidence that a large fraction of the metal-enriched galactic feedback material is efficiently retained within the Milky Way CGM. Furthermore, we observe significant sightline-to-sightline variation in inferred metallicities, pointing toward a highly anisotropic multi-phase CGM shaped by complex interactions between feedback outflows and cosmic accretion.

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Cite

BibTeXRIS
BibTeX
@misc{roy2026from,
  title = {{From Dispersion to Metallicity: Probing the Milky Way Circumgalactic Medium with Fast Radio Bursts}},
  author = {Manami Roy and Sanskriti Das and Smita Mathur and Anjali Gupta and Yair Krongold},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.40609},
  eprint = {2610.40609},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.40609},
}
RIS
TY  - UNPB
TI  - From Dispersion to Metallicity: Probing the Milky Way Circumgalactic Medium with Fast Radio Bursts
AU  - Manami Roy
AU  - Sanskriti Das
AU  - Smita Mathur
AU  - Anjali Gupta
AU  - Yair Krongold
PY  - 2026
DA  - 2026/10/29
PB  - arXiv
DO  - 10.48550/arxiv.2610.40609
UR  - https://arxiv.org/abs/2610.40609
AB  - Circumgalactic Medium (CGM) plays a critical role in galactic evolution, serving as the primary reservoir for accretion and outflows. In this work, we present a novel statistical analysis to derive CGM metallicity from the dispersion measure (DM) of 25 Fast Radio Burst (FRB) sightlines. By combining metallicity-dependent oxygen absorption DM estimates with metallicity-independent FRB DMs, we directly constrain the metallicity of the hot phase of the Milky Way (MW) CGM. Considering different diffuse baryon fractions (f_d = 0.0, 0.6, 0.8) in the Intergalactic Medium (IGM) and intervening halos, the median metallicities of CGM are Z_CGM = 0.12_−0.04^+0.09 Z_⊙, 0.26_−0.12^+0.18 Z_⊙, and 0.39_−0.20^+0.26 Z_⊙, respectively, by the bootstrapping method. Super-solar metallicity is seen in multiple sightlines for f_d=0.8, which is implausible for MW CGM metallicities. Even under conservative lower-bound estimates (f_d = 0.0), the inferred CGM metallicity significantly exceeds expectations for IGM accretion (Z_IGM ≲ 0.1 Z_⊙), providing strong empirical evidence that a large fraction of the metal-enriched galactic feedback material is efficiently retained within the Milky Way CGM. Furthermore, we observe significant sightline-to-sightline variation in inferred metallicities, pointing toward a highly anisotropic multi-phase CGM shaped by complex interactions between feedback outflows and cosmic accretion.
ER  -