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Abstract A sample of 14 FRBs with measured redshifts and scattering times is used to assess contributions to dispersion and scattering from the intergalactic medium (IGM), galaxy halos, and the disks of host galaxies. The IGM and galaxy halos contribute significantly to dispersion measures (DMs) but evidently not to scattering, which is then dominated by host galaxies. This enables the usage of scattering times for estimating DM contributions from host galaxies and also for a combined scattering–dispersion redshift estimator. Redshift estimation is calibrated using the scattering of Galactic pulsars after taking into account different scattering geometries for Galactic and intergalactic lines of sight. The DM-only estimator has a bias of ∼0.1 and rms error of ∼0.15 in the redshift estimate for an assumed ad hoc value of 50 pc cm−3for the host galaxy’s DM contribution. The combined redshift estimator shows less bias by a factor of 4 to 10 and a 20%–40% smaller rms error. We find that values for the baryonic fraction of the ionized IGMfigm≃ 0.85 ± 0.05 optimize redshift estimation using dispersion and scattering. Our study suggests that 2 of the 14 candidate galaxy associations (FRB 20190523A and FRB 20190611B) should be reconsidered.
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This content will become publicly available on April 1, 2026
Empirical estimation of host galaxy dispersion measure toward well-localized fast radio bursts
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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- PAR ID:
- 10618028
- Publisher / Repository:
- EDP Sciences
- Date Published:
- Journal Name:
- Astronomy & Astrophysics
- Volume:
- 696
- ISSN:
- 0004-6361
- Page Range / eLocation ID:
- A81
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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