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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, DM_host. The DM_hostis 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 DM_hostfor 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 DM_host^direct. We also explored possible correlations between DM_hostand some key global properties of galaxies. Methods.We used VLT/MUSE observations of the FRB hosts to estimate our empirical DM_host^direct. The method relies on estimating the DM contribution of both the FRB host galaxy’s interstellar medium (DM_host^ISM) and its halo (DM_host^halo) separately. For comparison purposes, we also provide an alternative indirect method for estimating DM_hostbased on the Macquart relation (DM_host^Macquart). Results.We find an average ⟨DM_host⟩ = 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 DM_hostand both the stellar masses and the star formation rates of their hosts galaxies. In contrast, we do not find any strong correlation between DM_hostand the redshift nor the projected distances to the center of the FRB hosts. Finally, we do not find any strong correlation between DM_host^directand DM_host^Macquart, although the average values of the two are consistent within the uncertainties. Conclusions.Our reported correlations between DM_host^directand stellar masses and/or the star formation rates of the galaxies could be used in future studies to improve the priors used in establishing DM_hostfor 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 DM_host^directand DM_host^directindicates that there may be contributions to the DM of FRBs not included in our DM_host^directmodeling, for example large DMs from the immediate environment of the FRB progenitor and/or intervening large-scale structures not accounted for in DM_host^Macquart. 

Abstract This paper presents the first public data release (DR1) of the FRB Line-of-sight Ionization Measurement From Lightcone AAOmega Mapping (FLIMFLAM) survey, a wide field spectroscopic survey targeted on the fields of 10 precisely localized fast radio bursts (FRBs). DR1 encompasses spectroscopic data for 10,468 galaxy redshifts across 10 FRB fields withz < 0.4, covering approximately 26 deg²of the sky in total. FLIMFLAM is composed of several layers, encompassing the “wide” (covering ∼degree or >10 Mpc scales), “narrow” (several arcminutes or ∼Mpc), and integral field unit (“IFU”; ∼arcminute or ∼100 kpc) components. The bulk of the data comprises spectroscopy from the Two Degree Field-AAOmega instrument on the 3.9 m Anglo-Australian Telescope, while most of the narrow and IFU data was achieved using an ensemble of 8–10 m class telescopes. We summarize the information on our selected FRB fields, the criteria for target selection, methodologies employed for data reduction, spectral analysis processes, and an overview of our data products. An evaluation of our data reveals an average spectroscopic completeness of 48.43%, with over 80% of the observed targets having secure redshifts. Additionally, we describe our approach to generating angular masks and calculating the target selection functions, setting the stage for the impending reconstruction of the matter density field. 

Abstract The repeating fast radio burst FRB 20190520B is an anomaly of the FRB population thanks to its high dispersion measure (DM = 1205 pc cm⁻³) despite its low redshift ofz_frb= 0.241. This excess has been attributed to a large host contribution of DM_host≈ 900 pc cm⁻³, far larger than any other known FRB. In this paper, we describe spectroscopic observations of the FRB 20190520B field obtained as part of the FLIMFLAM survey, which yielded 701 galaxy redshifts in the field. We find multiple foreground galaxy groups and clusters, for which we then estimated halo masses by comparing their richness with numerical simulations. We discover two separateM_halo> 10¹⁴M_⊙galaxy clusters atz= 0.1867 and 0.2170 that are directly intersected by the FRB sight line within their characteristic halo radiusr₂₀₀. Subtracting off their estimated DM contributions, as well that of the diffuse intergalactic medium, we estimate a host contribution of ${\mathrm{D}\mathrm{M}}_{\mathrm{h}\mathrm{o}\mathrm{s}\mathrm{t}}={430}_{-220}^{+140}$or ${280}_{-170}^{+140}\mathrm{p}\mathrm{c}{\mathrm{c}\mathrm{m}}^{-3}$(observed frame), depending on whether we assume that the halo gas extends tor₂₀₀or 2 ×r₂₀₀. This significantly smaller DM_host—no longer the largest known value—is now consistent with Hαemission measures of the host galaxy without invoking unusually high gas temperatures. Combined with the observed FRB scattering timescale, we estimate the turbulent fluctuation and geometric amplification factor of the scattering layer to be $\tilde{F}G\approx 4.5–11{\left({\mathrm{pc}}^2\mathrm{km}\right)}^{-1/3}$, suggesting that most of the gas is close to the FRB host. This result illustrates the importance of incorporating foreground data for FRB analyses both for understanding the nature of FRBs and to realize their potential as a cosmological probe.