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1. Searching for the Sources of Excess Extragalactic Dispersion of FRBs

   https://doi.org/10.3847/1538-4357/ace324  

   Simha, Sunil; Lee, Khee-Gan; Prochaska, J_Xavier; Khrykin, Ilya_S; Huang, Yuxin; Tejos, Nicolas; Marnoch, Lachlan; Ata, Metin; Bernales, Lucas; Bhandari, Shivani; et al (August 2023, The Astrophysical Journal)

   Abstract The FLIMFLAM survey is collecting spectroscopic data of field galaxies near fast radio burst (FRB) sight lines to constrain key parameters describing the distribution of matter in the Universe. In this work, we leverage the survey data to determine the source of the excess extragalactic dispersion measure (DM), compared to Macquart relation estimates of four FRBs: FRB20190714A, FRB20200906A, FRB20200430A, and FRB20210117A. By modeling the gas distribution around the foreground galaxy halos and galaxy groups of the sight lines, we estimate DM_halos, their contribution to the FRB DMs. The FRB20190714A sight line shows a clear excess of foreground halos which contribute roughly two-thirds of the observed excess DM, thus implying a sight line that is baryon dense. FRB20200906A shows a smaller but nonnegligible foreground halo contribution, and further analysis of the intergalactic medium is necessary to ascertain the true cosmic contribution to its DM. FRB20200430A and FRB20210117A show negligible foreground contributions, implying a large host galaxy excess and/or progenitor environment excess. 

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2. A Measurement of Circumgalactic Gas around Nearby Galaxies Using Fast Radio Bursts

   https://doi.org/10.3847/1538-4357/acbc7d  

   Wu, Xiaohan; McQuinn, Matthew (March 2023, The Astrophysical Journal)

   Abstract The distribution of gas in the circumgalactic medium (CGM) of galaxies of all types is poorly constrained. Foreground CGMs contribute an extra amount to the dispersion measure (DM) of fast radio bursts (FRBs). We measure this DM excess for the CGMs of 10¹¹–10¹³M_⊙halos using the CHIME/FRB first data release, a halo mass range that is challenging to probe in any other way. Because of the uncertainty in the FRBs’ angular coordinates, only for nearby galaxies is the localization sufficient to confidently associate them with intersecting any foreground halo. Thus we stack on galaxies within 80 Mpc, optimizing the stacking scheme to approximately minimize the stack’s variance and marginalize over uncertainties in FRB locations. The sample has 20–30 FRBs intersecting halos with masses of 10¹¹–10¹²M_⊙and also of 10¹²–10¹³M_⊙, and these intersections allow a marginal 1σ–2σdetection of the DM excess in both mass bins. The bin of 10¹¹–10¹²M_⊙halos also shows a DM excess at 1–2 virial radii. By comparing data with different models for the CGM gas profile, we find that all models are favored by the data up to 2σlevel compared to the null hypothesis of no DM excess. With 3000 more bursts from a future CHIME data release, we project a 4σdetection of the CGM. Distinguishing between viable CGM models by stacking FRBs with CHIME-like localization would require tens of thousands of bursts. 

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3. FLIMFLAM DR1: The First Constraints on the Cosmic Baryon Distribution from Eight Fast Radio Burst Sight Lines

   https://doi.org/10.3847/1538-4357/ad6567  

   Khrykin, Ilya_S; Ata, Metin; Lee, Khee-Gan; Simha, Sunil; Huang, Yuxin; Prochaska, J_Xavier; Tejos, Nicolas; Bannister, Keith_W; Cooke, Jeff; Day, Cherie_K; et al (September 2024, The Astrophysical Journal)

   Abstract The dispersion measure of fast radio bursts (FRBs), arising from the interactions with free electrons along the propagation path, constitutes a unique probe of the cosmic baryon distribution. Their constraining power is further enhanced in combination with observations of the foreground large-scale structure and intervening galaxies. In this work, we present the first constraints on the partition of the cosmic baryons between the intergalactic medium (IGM) and circumgalactic medium (CGM), inferred from the FLIMFLAM spectroscopic survey. In its first data release, the FLIMFLAM survey targeted galaxies in the foreground of eight localized FRBs. Using Bayesian techniques, we reconstruct the underlying ∼Mpc-scale matter density field that is traced by the IGM gas. Simultaneously, deeper spectroscopy of intervening foreground galaxies (at impact parametersb_⊥≲r₂₀₀) and the FRB host galaxies constrains the contribution from the CGM. Applying Bayesian parameter inference to our data and assuming a fiducial set of priors, we infer the IGM cosmic baryon fraction to be $f_{\mathrm{igm}}={0.59}_{-0.10}^{+0.11}$and a CGM gas fraction of $f_{\mathrm{gas}}={0.55}_{-0.29}^{+0.26}$for 10¹⁰M_⊙≲M_halo≲ 10¹³M_⊙halos. The mean FRB host dispersion measure (rest-frame) in our sample is $〈{\mathrm{DM}}_{\mathrm{host}}〉={90}_{-19}^{+29}\mathrm{pc}{\mathrm{cm}}^{-3}$, of which $〈{\mathrm{DM}}_{\mathrm{host}}^{\mathrm{unk}}〉={69}_{-19}^{+28}\mathrm{pc}{\mathrm{cm}}^{-3}$arises from the host galaxy interstellar medium (ISM) and/or the FRB progenitor environment. While our currentf_igmandf_gasuncertainties are too broad to constrain most galactic feedback models, this result marks the first measurement of the IGM and CGM baryon fractions, as well as the first systematic separation of the FRB host dispersion measure into two components: arising from the halo and from the inner ISM/FRB engine. 

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4. Modelling the cosmic dispersion measure in the D < 120 Mpc Local Universe

   https://doi.org/10.1093/mnras/staf417  

   Huang, Yuxin; Lee, Khee-Gan; Libeskind, Noam I; Simha, Sunil; Valade, Aurélien; Prochaska, J Xavier (March 2025, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT The Local Universe ($D< 120$ Mpc) has been intensely studied for decades, with highly complete galaxy redshift surveys now publicly available. These data have driven density reconstructions of the underlying matter density field, as well as constrained simulations that aim to reproduce the observed structures. In this paper, we introduce a dispersion measure (DM) model that makes use of this detailed knowledge of our Local Universe within $D< 120$ Mpc. The model comprises three key components: (i) the DM from the Milky Way’s halo and the intragroup medium (up to 3.4 Mpc), derived from the H estia simulations, a series of constrained hydrodynamic simulations designed to reproduce our Local Group; (ii) the DM contribution from the large-scale intergalactic medium beyond the Local Group (3.4 Mpc $< D< 120$ Mpc), calculated using the Hamlet reconstructed matter density field; and (iii) the individual DM contributions from Local Universe galaxy haloes and clusters based on data from the Two Micron All Sky Survey Galaxy Group Catalogue and the NASA/IPAC Extragalactic Data base. This comprehensive model will be made available as a python package. As the most realistic model to date for DM in the local volume, it promises to improve the constraints of DM contributions from the intergalactic medium and circumgalactic medium of fast radio bursts (FRBs), thereby enhancing the accuracy of cosmic baryon distribution calculations based on DM analysis of FRBs. 

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5. Measuring the Variance of the Macquart Relation in Redshift–Extragalactic Dispersion Measure Modeling

   https://doi.org/10.3847/1538-4357/ad2705  

   Baptista, Jay; Prochaska, J. Xavier; Mannings, Alexandra G.; James, C. W.; Shannon, R. M.; Ryder, Stuart D.; Deller, A. T.; Scott, Danica R.; Glowacki, Marcin; Tejos, Nicolas (April 2024, The Astrophysical Journal)

   Abstract The Macquart relation describes the correlation between the dispersion measure (DM) of fast radio bursts (FRBs) and the redshiftzof their host galaxies. The scatter of the Macquart relation is sensitive to the distribution of baryons in the intergalactic medium including those ejected from galactic halos through feedback processes. The variance of the distribution in DMs from the cosmic web (DM_cosmic) is parameterized by a fluctuation parameterF. In this work, we present a new measurement ofFusing 78 FRBs of which 21 have been localized to host galaxies. Our analysis simultaneously fits for the Hubble constantH₀and the DM distribution due to the FRB host galaxy. We find that the fluctuation parameter is degenerate with these parameters, most notablyH₀, and use a uniform prior onH₀to measure ${\log }_{10}F>-0.86$at the 3σconfidence interval and a new constraint on the Hubble constant $H_0={85.3}_{-8.1}^{+9.4}\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$. Using a synthetic sample of 100 localized FRBs, the constraint on the fluctuation parameter is improved by a factor of ∼2. Comparing ourFmeasurement to simulated predictions from cosmological simulation (IllustrisTNG), we find agreement between redshifts 0.4 <z andz< 2.0. However, atz< 0.4, the simulations underpredictF, which we attribute to the rapidly changing extragalactic DM excess distribution at low redshift. 

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