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Register a new userThe dispersion measure and scattering of FRBs: Contributions from the intergalactic medium, foreground halos, and hosts
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We investigate the dispersion measure(DM) and scattering of FRBs by the intergalactic-medium(IGM), foreground and host halos, using cosmological hydrodynamical simulation. We find that the median DM caused by foreground halos is around 30% of that caused by the IGM, but has a much larger variance. The DM induced by hosts deviates from a log-normal distribution, but exhibits an extended distribution in the range of $1-3000 {rm{pc, cm^{-3}}}$ with a median value $sim 100 {rm{pc, cm^{-3}}}$. Then we produce mock FRB sources, assuming a uniform distribution in the range $zsim 0-0.82$, to consider the propagation effect of IGM, foreground and host halos on FRB signals simultaneously. The DM distribution of mock sources agrees well with the observation. The fitted DM-redshift relation of the mock sources can provide a rough estimation of the redshifts of observed events with errors $delta z lesssim 0.15$. The distribution of mock sources in the DM-scattering time($tau$) space can also match the observation, assuming a Kolmogorov turbulence model with the inner and outer scale is 1000 km to 1 AU, and 0.2-10 pc respectively. Finally, we estimate the relative importance of these medium on DM and $tau$ in our models. The IGM and host halos are the primary and secondary sources to the extragalactic DM, $rm{DM_{exg}}$. Meanwhile, the contribution from foreground halos increases as $rm{DM_{exg}}$ increases. The host and foreground halos may be the most important medium for scattering. Statistically, the latter may dominate the scattering of events with $rm{DM_{exg}} gtrsim 200 {rm{pc, cm^{-3}}}$.
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The scattering of fast radio bursts (FRBs) by the intergalactic medium (IGM) is explored using cosmological hydrodynamical simulations. We confirm that the scattering by the clumpy IGM has significant line-of-sight variations. We demonstrate that the scattering by the IGM in the voids and walls of the cosmic web is weak, but it can be significantly enhanced by the gas in clusters and filaments. The observed non-monotonic dependence of the FRB widths on the dispersion measures (DM) cannot determine whether the IGM is an important scattering matter or not. The IGM may dominate the scattering of some FRBs, and the host galaxy dominates others. For the former case, the scattering should be primarily caused by the medium in clusters. A mock sample of 500 sources shows that $tau_{rm{IGM}} propto rm{DM_{IGM}}^{1.6-2.1}$ at $z<1.5$. Assuming that the turbulence follows Kolmogorov scaling, we find that an outer scale of $L_0sim 5,$pc is required to make $tau_{rm{IGM}} sim 1-10,$ms at $ u=1, $ GHz. The required $L_0sim 5, $pc can alleviate the tension in the timescales of turbulent heating and cooling but is still $sim 4$ orders of magnitude lower than the presumed injection scale of turbulence in the IGM. The gap is expected to be effectively shortened if the simulation resolution is further increased. The mechanisms that may further reduce the gap are shortly discussed. If future observations can justify the role of the IGM in the broadening of FRBs, it can help to probe the gas in clusters and filaments.
Using the results of the IllustrisTNG simulation we estimate the dispersion measure which may be attributed to halos of so called host galaxies of fast radio bursts sources (FRBs). Our results show that in contradiction to assumptions used to show the applicability of FRBs to cosmological tests, both the dispersion measure and its standard deviation calculated for host galaxies with given stellar mass in general increase with the redshift. The effect is not strong and cosmological tests using FRBs will be possible, but to preserve the level of statistical uncertainty the number of FRBs with known redshift in a sample should be increased by 15%--35% depending on circumstances. We show various statistical characteristics of ionized gas surrounding galaxies, the resulting dispersion measure and their dependence on the host galaxy stellar mass, redshift, and the projected distance of a FRB source from its host center. Cosmology: theory -- Galaxies: halos -- large-scale structure of Universe
Fast Radio Burst (FRB) dispersion measures (DMs) record the presence of ionized baryons that are otherwise invisible to other techniques enabling resolution of the matter distribution in the cosmic web. In this work, we aim to estimate the contribution to FRB 180924 DM from foreground galactic halos. Localized by ASKAP to a massive galaxy, this sightline is notable for an estimated cosmic web contribution to the DM ($rm DM_{cosmic} = 220~pc~cm^{-3}$), which is less than the average value at the host redshift ($rm z = 0.3216$) estimated from the Macquart relation ($280~rm pc~cm^{-3}$). In the favored models of the cosmic web, this suggests few intersections with foreground halos at small impact parameters ($lesssim 100$ kpc). To test this hypothesis, we carried out spectroscopic observations of the field galaxies within $sim$1 of the sightline with VLT/MUSE and Keck/LRIS. Furthermore, we developed a probabilistic methodology that leverages photometric redshifts derived from wide-field DES and WISE imaging. We conclude that there is no galactic halo that closely intersects the sightline and also that the net DM contribution from halos, $rm DM_{halos}< 45~pc~cm^{-3}$ (95 % c.l.). This value is lower than the $rm DM_{halos}$ estimated from an average sightline ($121~rm pc~cm^{-3}$) using the Planck $Lambda CDM$ model and the Aemulus halo mass function and reasonably explains its low $rm DM_{cosmic}$ value. We conclude that FRB 180924 represents the predicted majority of sightlines in the universe with no proximate foreground galactic halos. Our framework lays the foundation for a comprehensive analysis of FRB fields in the near future.
The backbone of the large-scale structure of the Universe is determined by processes on a cosmological scale and by the gravitational interaction of the dominant dark matter. However, the mobile baryon population shapes the appearance of these structures. Theory predicts that most of the baryons reside in vast unvirialized filamentary structures that connect galaxy groups and clusters, but the observational evidence is currently lacking. Because the majority of the baryons are supposed to exist in a large-scale, hot and dilute gaseous phase, X-rays provide the ideal tool to progress our understanding. Observations with the Athena+ X-ray Integral Field Unit will reveal the location, chemical composition, physical state and dynamics of the active population of baryons.
The recently discovered fast radio bursts (FRBs), presumably of extra-galactic origin, have the potential to become a powerful probe of the intergalactic medium (IGM). We point out a few such potential applications. We provide expressions for the dispersion measure and rotation measure as a function of redshift, and we discuss the sensitivity of these measures to the HeII reionization and the IGM magnetic field. Finally we calculate the microlensing effect from an isolate, extragalctic stellar-mass compact object on the FRB spectrum. The time delays between the two lensing images will induce constructive and destructive interference, leaving a specific imprint on the spectra of FRBs. With a high all-sky rate, a large statistical sample of FRBs is expected to make these applications feasible.
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