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Context.Fast radio bursts (FRBs) are very energetic pulses in the radio wavelengths that have an unknown physical origin. They can be used to study the intergalactic medium thanks to their dispersion measure (DM). The DM has several contributions that can be measured (or estimated), including the contribution from the host galaxy itself, DMhost. The DMhostis generally difficult to measure, thus limiting the use of FRBs as cosmological probes and our understanding of their physical origin(s). Aims.In this work we empirically estimated DMhostfor a sample of 12 galaxy hosts of well-localized FRBs at 0.11 < z < 0.53 using a direct method based solely on the properties of the host galaxies themselves, referred to as DMhostdirect. We also explored possible correlations between DMhostand some key global properties of galaxies. Methods.We used VLT/MUSE observations of the FRB hosts to estimate our empirical DMhostdirect. The method relies on estimating the DM contribution of both the FRB host galaxy’s interstellar medium (DMhostISM) and its halo (DMhosthalo) separately. For comparison purposes, we also provide an alternative indirect method for estimating DMhostbased on the Macquart relation (DMhostMacquart). Results.We find an average ⟨DMhost⟩ = 80 ± 11 pc cm−3with a standard deviation of 38 pc cm−3(in the rest frame) using our direct method, with a systematic uncertainty of ∼30%. This is larger than the typically used value of 50 pc cm−3but consistent within the uncertainties. We report positive correlations between DMhostand both the stellar masses and the star formation rates of their hosts galaxies. In contrast, we do not find any strong correlation between DMhostand the redshift nor the projected distances to the center of the FRB hosts. Finally, we do not find any strong correlation between DMhostdirectand DMhostMacquart, although the average values of the two are consistent within the uncertainties. Conclusions.Our reported correlations between DMhostdirectand stellar masses and/or the star formation rates of the galaxies could be used in future studies to improve the priors used in establishing DMhostfor individual FRBs. Similarly, such correlations and the lack of a strong redshift evolution can be used to constrain models for the progenitor of FRBs, for example by comparing them with theoretical models. However, the lack of correlation between DMhostdirectand DMhostdirectindicates that there may be contributions to the DM of FRBs not included in our DMhostdirectmodeling, for example large DMs from the immediate environment of the FRB progenitor and/or intervening large-scale structures not accounted for in DMhostMacquart.
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This content will become publicly available on November 6, 2026
Evidence for a Hot Galactic Halo around the Andromeda Galaxy Using Fast Radio Bursts along Two Sightlines
Abstract Fast radio bursts (FRBs) are millisecond-duration radio transients that serve as unique probes of ionizedextragalactic matter. We report the discovery and localization of two FRBs piercing the Andromeda galaxy (M31) with the realfast transient-detection system at the Very Large Array. These unique sightlines enable constraints on M31’s electron density distribution. We localized FRB 20230930A to a host galaxy at redshiftz= 0.0925 and FRB 20230506C to a host galaxy at redshiftz= 0.3896. After accounting for the dispersion contributions from the Milky Way, the host galaxies, and the intergalactic medium, we estimate M31’s contribution to be 26–239 pc cm−3toward FRB 20230930A and 51–366 pc cm−3toward FRB 20230506C, within the 90% credible interval (CI). By modeling the M31 disk’s contribution, we isolate the halo component and find that M31’s halo contributes 7–169 pc cm−3along FRB 20230930A (90% CI). The inferred values of DMM31,halofrom the FRBs are consistent with predictions from a modified Navarro–Frenk–White profile at the corresponding impact parameter. The cool and warm phase gas is unlikely to account for the DMM31,halounless the ionization fraction is as high as 90%. While limited to two sightlines, these results offer tentative evidence for the existence of a hot halo surrounding M31. We also discuss the potential contribution of other foreground structures, particularly in explaining the DM excess observed in FRB 20230506C. This work demonstrates how FRBs can be used to probe the circumgalactic medium of intervening galaxies.
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- Award ID(s):
- 2107070
- PAR ID:
- 10651728
- Publisher / Repository:
- IOP
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 993
- Issue:
- 2
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 221
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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