{"id":"a7eb1851-bba1-49d3-9c85-66724169e7a3","arxiv_id":"2501.14063","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":6,"one_line_summary":"Using MUSE H-alpha emission and halo modeling, the authors estimate rest-frame host DM for 12 FRBs, finding an average of 80 +/- 11 pc cm^-3 and correlations with stellar mass and star formation rate.","lead":"This paper estimates how much of a fast radio burst's signal delay comes from gas in its host galaxy, using spectra of 12 host galaxies. The average host contribution is about 80 pc cm^-3, higher than the usual 50 pc cm^-3 assumption.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The quoted ~30% systematic uncertainty is internally inconsistent with the paper's own admission that Eq. 6 parameters can change DM_ISM by factors of 2-3, so the central 80±11 pc/cm3 average is not robust at the stated precision.","rationale":"The reader's weakest assumption points to the Eq. 6 calibration; I agree in direction but sharpen the issue. The problem is not merely that the Milky Way calibration may not transfer to FRB hosts; it is that the paper's own Section 3.1.4 acknowledges a factor-2-to-3 range in DM_ISM from the unmeasured parameters, while Section 4.5 propagates only a ±50% sub-range and then reports a ~30% systematic on DM_direct. Since DM_ISM dominates the summed DM_direct, this internal inconsistency directly affects the headline average and its stated uncertainty. The paper is transparent about the assumptions and about treating two upper limits as measurements, which is a credit, but the abstract's precision is not supported by the full stated parameter range. The correlations are also partly built into the method: DM_ISM is derived from H-alpha, a direct SFR tracer, and DM_halo is derived from stellar mass via abundance matching, so positive correlations with SFR and stellar mass are expected by construction. The authors acknowledge this through the SFMS experiment, but the strength of the correlation claims is correspondingly reduced. These issues do not warrant rejection: the homogeneous MUSE sample and the explicit comparison with the Macquart-based estimates are useful, and the conditional verdict already captures the need for revision. UNCHANGED is therefore the right call: the reader's conditional verdict stands, with the systematic uncertainty concern now sharpened into a concrete internal inconsistency.","tokens_in":23020,"tokens_out":8933,"duration_ms":86142,"concrete_test":"Recompute all DM_direct entries in Table 4 with the bracketing parameter values admitted in Section 3.1.4: (a) multiply the Eq. 6 bracket by 2 and by 1/3, and (b) set L_kpc to the physical diameter of the 0.4-arcsec MUSE aperture at each host redshift while keeping f_f=1, zeta=1, tau=2. If the resulting ensemble mean moves outside 80±30 pc/cm3, or if the reported SFR/mass correlation p-values change by more than an order of magnitude, then the 30% systematic claim and the quoted correlations should be re-presented as a model-dependent range rather than as an empirical measurement.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The headline quantity is dominated by DM_ISM, not DM_halo: in Table 4 the DM_ISM entries range from roughly 20 to 132 pc cm^-3 while DM_halo entries are 14-44 pc cm^-3. Equation 6 is controlled by four unmeasured quantities (f_f, zeta, tau, L_kpc), and Section 3.1.4 states explicitly that changing these values can make DM_ISM up to 2-3 times larger or smaller than the fiducial values. Yet Section 4.5 propagates the systematic effect by rescaling each DM_ISM with a mean drawn only from [0.5,1.5] times the fiducial value, yielding the quoted ~30% systematic on DM_direct. That sampling range does not cover the factor-2-to-3 spread the same paper admits, so the abstract's 'systematic uncertainty of ~30%' is not a bound on the model assumptions; it is a bound on one arbitrarily chosen sub-range. Because DM_ISM dominates, the central <DM_host>=80±11 pc/cm3 can shift by tens of pc/cm3 under the admitted but unsampled parameter values. This does not destroy the value of the pilot sample, but it means the central quantitative claim is not established at the stated precision.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper presents an empirical estimate of the host-galaxy dispersion measure (DM_host) for 12 well-localized fast radio bursts, using VLT/MUSE H-alpha observations for the interstellar medium contribution and abundance matching plus a modified Navarro-Frenk-White profile for the halo contribution. The authors report a rest-frame average of <DM_host> = 80 +/- 11 pc cm^-3 with a standard deviation of 38 pc cm^-3 and a claimed systematic uncertainty of ~30%. They also report positive correlations between DM_host and host stellar mass and star-formation rate, no strong correlation with redshift or projected offset, and no significant correlation between the direct and Macquart-based DM_host estimates. The paper is clearly written, uses a homogeneous observational sample, and includes detailed Monte Carlo uncertainty propagation.","tokens_in":1567,"tokens_out":2019,"duration_ms":73406,"significance":"If the central estimate were robust, this would be a valuable result: it would replace the commonly assumed fixed value of 50 pc cm^-3 with a homogeneous, observationally grounded distribution, and the reported correlations could improve priors for individual FRB analyses and constrain progenitor models. The paper's strengths include transparent Monte Carlo error propagation for both the H-alpha-based and halo-based components, a well-defined sample with public data, and an explicit comparison against an independent Macquart-relation estimate. The reported absence of redshift evolution and the weak offset dependence are also useful falsifiable statements. However, the systematic uncertainty treatment and the handling of non-detections currently prevent the quantitative headline claims from being accepted at face value.","major_comments":[{"comment":"The systematic uncertainty estimate samples the mean of DM_ISM uniformly in [0.5, 1.5] times the fiducial value, but Section 3.1.4 states that the parameters of Equation 6 can make DM_ISM 'up to 2 (3) times larger (smaller)'. The [0.5, 1.5] range does not cover the admitted factor-of-2-to-3 spread. Since DM_ISM dominates DM_direct (Table 4), the quoted ~30% systematic uncertainty is not a bound on the model assumptions, and the headline <DM_host> = 80 +/- 11 pc cm^-3 is not established at the stated precision. Please expand the systematic exploration to the full admitted range or revise the claimed precision accordingly.","section":"Section 4.5"},{"comment":"FRB20190611B and FRB20210117A have local H-alpha non-detections reported as 2-sigma upper limits in Table 3, yet they are included in the sample average as actual measurements, with DM_ISM values of approximately 32 and 20 pc cm^-3 (Table 4). Treating upper limits as detections can bias the mean upward, and the justification that systematic uncertainties are larger is not a statistical substitute for a proper treatment. Please provide a sensitivity test (e.g., setting DM_ISM to zero or to the upper limit bound for these objects) or use a survival-analysis approach, and discuss how the reported average changes.","section":"Section 3.1.4"},{"comment":"The reported positive correlation between DM_direct and stellar mass is largely built into the method: DM_halo is derived from stellar mass through abundance matching and a monotonic mNFW profile (Section 3.1.3, Equation 7), so a positive correlation is guaranteed by construction. The independent empirical content is in DM_ISM (Pearson coefficient 0.64, p = 0.03), which is only marginally significant. The manuscript should either explicitly frame the DM_host-M* correlation as a consequence of the assumed halo model rather than an independent empirical finding, or provide a test that removes the mechanical contribution (e.g., by examining the residual after subtracting the model expectation).","section":"Section 4.2"},{"comment":"The halo component adopts f_hot = 55% as a fixed fiducial value, and the systematic uncertainty analysis in Section 4.5 does not vary f_hot or the mNFW profile parameters. DM_halo contributes 14-44 pc cm^-3 across the sample (Table 4), so an uncertainty in f_hot of, say, +/-10-20% could shift the ensemble average by several pc cm^-3. Please include f_hot (and, if feasible, the profile parameters) in the systematic budget, or justify quantitatively why their effect is negligible compared with the DM_ISM uncertainties.","section":"Section 3.1.3"}],"minor_comments":[{"comment":"The abstract in the posted version gives the mean as '80+/-11 pc/cc'; the rest of the paper uses 'pc cm^-3'. Please use consistent units throughout.","section":"Abstract"},{"comment":"The caption states that the trend line 'has a slope of 1 by construction'; please clarify what parameter is fitted (e.g., a multiplicative offset) and how the 19% systematic difference is derived.","section":"Figure 2"},{"comment":"The phrase 'these can make the DM_ISM up to 2 (3) times larger (smaller)' is ambiguous; please specify which combinations of f_f, zeta, tau, and L_kpc produce the larger and smaller extremes.","section":"Section 3.1.4"},{"comment":"For FRB20190711A, the global H-alpha flux is 16.1 +/- 16.6, which is consistent with zero. Please add a note explaining how this non-detection-level global value is handled and whether it affects the global/local comparison in Figure 2.","section":"Table 3"},{"comment":"The entry for Prochaska et al. (2023) contains a garbled author name ('almannin'); please correct the citation.","section":"References"}],"recommendation":"major_revision","confidential_remarks":"The paper is honest and well-structured, but the systematic uncertainty estimate is not commensurate with the paper's own admission of factor-of-2-3 variations in Equation 6. The correlation with stellar mass is partly a construction artifact, and the treatment of upper limits as detections needs a robustness check. These issues are fixable and do not undermine the value of the pilot sample, which is why I recommend major revision rather than rejection."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"You should know two things about this paper before reading it. First, it gives the first homogeneous set of empirical DM_host estimates for 12 well-localized FRB hosts, using MUSE H-alpha maps for the ISM term and abundance-matched mNFW halos for the halo term. Several of these hosts had no previous DM_host estimate, so as a pilot data set it is genuinely useful. Second, the headline average of 80±11 pc/cm3 with a '~30% systematic' is not as robust as it sounds: the quoted systematic comes from sampling the ISM conversion parameters over a factor 1.5 range, while the same paper admits those parameters can change DM_ISM by factors of 2-3. The central value may be roughly right, but the stated precision is not earned.\n\nWhat the paper does well: the analysis is transparent, the Monte Carlo propagation is careful, the tables and appendix figures are complete, and the authors routinely flag their own assumptions. The comparison between local and global H-alpha, and the SFMS experiment in Section 4.2, are honest attempts to see how much of the correlation signal is built in. I also credit the discussion of the missing correlation between DM_direct and DM_Macquart—they do not paper over the fact that their modeling may be missing something.\n\nThe soft spots are real but proportionate. The DM_host-stellar mass correlation is largely construction: DM_halo is computed from stellar mass through a monotonic relation, so the p=0.07 correlation in DM_direct is not evidence of a physical scaling. The SFR correlation is stronger (p=0.004), but H-alpha directly enters DM_ISM, so part of that is also expected. The two non-detections treated as measurements are a reasonable choice given the systematic budget, but should be shown as upper limits in the main figures. And the inconsistency between the admitted factor 2-3 systematic in Eq. 6 and the 1.5x sampling range used in Section 4.5 should be fixed—either by expanding the systematic exploration or by clearly labeling the 30% as a conditional estimate, not a bound.\n\nWho is this for? Anyone building DM_host priors for FRB cosmology, or comparing host properties to progenitor models. It deserves a serious referee, with the expectation of revision on the systematic-uncertainty framing and correlation interpretation. I'd accept it for review, and I'd cite the sample values with a caveat on the systematics.","headline":"A transparent, useful pilot measurement of host-galaxy DMs for 12 FRBs, but the headline precision is overstated and the mass correlation is partly built into the method.","tokens_in":23899,"tokens_out":2981,"would_cite":true,"duration_ms":25192,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"The paper claims that the host galaxies of fast radio bursts contribute, on average, a rest-frame dispersion measure of about 80 pc cm^-3, not the fixed 50 pc cm^-3 widely assumed, and that this contribution scales with host stellar mass…","keywords":["fast radio bursts","dispersion measure","host galaxy","H-alpha emission","circumgalactic medium","Macquart relation","VLT/MUSE","star formation rate"],"falsifier":"Measure electron columns along the same FRB sightlines with an independent tracer, such as Faraday rotation measure combined with a magnetic-field estimate from the burst environment; if the resulting DM_ISM values disagree systematically with the H-alpha-based values beyond the stated ~30% systematic budget, the assumed clumpiness and path-length calibration fails.","tokens_in":22861,"feed_emoji":"📡","tokens_out":4900,"duration_ms":46326,"temperature":0.7,"pith_summary":"This paper tries to establish that the host galaxies of fast radio bursts contribute an average rest-frame dispersion measure of about 80 pc $cm^{-3}$, not the fixed 50 pc $cm^{-3}$ commonly assumed. The authors estimate this directly for twelve well-localized FRB hosts using VLT/MUSE spectroscopy, separating the interstellar gas contribution from the halo gas contribution and using H-$\\alpha$ surface brightness near the burst to trace the ISM. They report that the host contribution grows with stellar mass and star formation rate and does not evolve strongly with redshift out to roughly z = 0.5. A sympathetic reader should care because the correlations give a physically motivated prior for DM_host in future FRB cosmology, and the average value, if right, corrects a standard assumption used across many FRB analyses.","feed_headline":"FRB host galaxies add 80 pc cm^-3 of dispersion, on average","feed_subtitle":"Twelve well-mapped host galaxies put the host contribution near 80 pc cm^-3 and tie it to stellar mass and star formation.","key_machinery":"The central object is the decomposition DM_host^direct = DM_host^ISM + DM_host^halo. DM_ISM is obtained from observed H-$\\alpha$ surface brightness via Reynolds' emission-measure relation, converted to DM with an equation that assumes Milky Way values for cloud volume-filling factor, internal density variation, inter-cloud contrast, and path length L_kpc = 0.15. DM_halo is obtained by converting stellar masses to halo masses with the Moster abundance-matching relation, placing the gas in a modified NFW profile with an assumed ionized baryon fraction f_hot = 55%, and integrating along the line of sight from the FRB's projected offset to the halo boundary r_200. This two-term sum carries the argument because it turns galaxy photometry and spectroscopy into a physical prediction for the host contribution to the dispersion measure.","core_discovery":"The paper reports an average host dispersion measure of <DM_host> = 80 +/- 11 pc $cm^{-3}$ with a standard deviation of 38 pc $cm^{-3}$ in the rest frame, obtained by summing an ISM term and a halo term for each of twelve host galaxies. It reports positive correlations of DM_host with stellar mass and star formation rate, with Pearson coefficients of 0.73 and 0.85 respectively, and a flat redshift evolution with power-law index $\\alpha$ ~ 0.3 +/- 1.7. The direct estimates do not correlate with the indirect Macquart-relation estimates, even though the ensemble averages agree within uncertainties; the paper interprets this as evidence of additional DM contributions not captured by the model.","pith_inferences":["These twelve hosts are mostly star-forming galaxies near the main sequence; if future samples include quiescent early-type hosts, the DM_host versus star-formation-rate correlation could steepen or flatten, and the average near 80 pc cm^-3 might not generalize to all FRB environments.","A natural extension the paper does not build is to convert the reported DM_host(M_star, SFR) fits into a ready-made Bayesian prior for FRB cosmology, which is the direct use case implied by the conclusions.","The apparent low-redshift versus high-redshift discrepancy between direct and Macquart estimates could be tested with a larger sample; if it persists, it would argue for a redshift-dependent unmodeled contribution rather than small-number statistics.","The halo term could be validated independently by comparing its predictions with X-ray or absorption-line measurements of warm-hot halo gas in the same hosts."],"forward_implications":["The commonly used fixed prior DM_host = 50 pc cm^-3 should give way to a broader distribution centered near 80 pc cm^-3 with a scatter of about 38 pc cm^-3 for FRB hosts in this redshift range.","New FRB hosts with high stellar mass or high star formation rate should be assigned larger DM_host priors, following the reported relations of roughly 43 pc cm^-3 per decade in stellar mass and 36 pc cm^-3 per decade in star formation rate.","If the flat redshift trend holds out to z ~ 0.5, no extra redshift-dependent host correction is needed for cosmological DM estimates in this range.","The lack of correlation between the direct and Macquart-based estimates implies that some FRB sightlines carry additional DM from the progenitor environment or intervening large-scale structure that the current two-term model does not capture.","Comparing the reported correlations with theoretical FRB population models can discriminate among progenitor scenarios, since different models predict different DM_host scaling with galaxy properties."],"supporting_citations":[{"why":"Supplies the equation and procedure for converting H-alpha emission measure into DM_ISM and applies it to an FRB host.","marker":"Tendulkar et al. (2017)"},{"why":"Provides the emission-measure relationship from H-alpha surface brightness that anchors the ISM term.","marker":"Reynolds (1977)"},{"why":"Applies the same ISM method to an FRB host and supplies a comparison point for the direct approach.","marker":"Chittidi et al. (2020)"},{"why":"Provides the modified NFW halo profile and line-of-sight integration used to estimate DM_halo.","marker":"Prochaska & Zheng (2019)"},{"why":"Supplies the abundance-matching relation that turns stellar mass into halo mass for the halo term.","marker":"Moster et al. (2013)"},{"why":"Supplies the Macquart relation and scatter model used for the indirect DM_host estimates.","marker":"Macquart et al. (2020)"},{"why":"Provides an independent DM_host estimate from a different methodology used as a consistency check.","marker":"Khrykin et al. (2024b)"}],"fun_headline_variants":["FRB host galaxies add ~80 pc cm^-3 to dispersion","Host DM halos: 80 pc cm^-3, scaling with stellar mass and star formation","Direct host DM estimates for 12 FRBs average 80 pc cm^-3","FRB host DM: 80 pc cm^-3, but direct and indirect methods don't correlate"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The result depends on converting H-alpha brightness to a gas column using a Milky Way-calibrated relation that assumes dense, turbulent, clumpy gas with a fixed 0.15 kpc path length; if the ionized gas in FRB-host galaxies is smoother, thinner, or differently clumped, or if bursts lie outside the disks, the average DM_host could shift by factors of two to three.","fun_headline_variants_meta":{"raw":{"variants":["FRB host galaxies add ~80 pc cm^-3 to dispersion","Host DM halos: 80 pc cm^-3, scaling with stellar mass and star formation","Direct host DM estimates for 12 FRBs average 80 pc cm^-3","FRB host DM: 80 pc cm^-3, but direct and indirect methods don't correlate"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000685,"raw_usage":{"total_tokens":3167,"prompt_tokens":1068,"completion_tokens":2099,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":684,"completion_tokens_details":{"reasoning_tokens":2008}},"tokens_in":684,"tokens_out":2099,"duration_ms":12687,"temperature":1.0,"reasoning_tokens":2008,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-10T15:24:46.491504+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure electron columns along the same FRB sightlines with an independent tracer, such as Faraday rotation measure combined with a magnetic-field estimate from the burst environment; if the resulting DM_ISM values disagree systematically with the H-alpha-based values beyond the stated ~30% systematic budget, the assumed clumpiness and path-length calibration fails.","supporting_citations":[{"cited_title":"P., Bassa, C","cited_arxiv_id":null,"evidence_quote":"Supplies the equation and procedure for converting H-alpha emission measure into DM_ISM and applies it to an FRB host."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the emission-measure relationship from H-alpha surface brightness that anchors the ISM term."},{"cited_title":"S., Simha, S., Mannings, A., et al","cited_arxiv_id":null,"evidence_quote":"Applies the same ISM method to an FRB host and supplies a comparison point for the direct approach."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the modified NFW halo profile and line-of-sight integration used to estimate DM_halo."}],"review_version":1}