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Register a new userIntergalactic medium dispersion measures of fast radio bursts estimated from IllustrisTNG simulation and their cosmological applications
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Fast radio bursts (FRBs) are millisecond-duration radio transients and can be used as a cosmological probe. However, the dispersion measure (DM) contributed by intergalactic medium (IGM) is hard to be distinguished from other components. In this paper, we use the IllustrisTNG simulation to realistically estimate the $DM_{rm IGM}$ up to $zsim 9$. We find $DM_{rm IGM} = 892^{+721}_{-270}$ pc cm$^{-3}$ at $z=1$. The probability distribution of $DM_{rm IGM}$ can be well fitted by a quasi-Gaussian function with a long tail. The tail is caused by the structures along the line of sight in IGM. Subtracting DM contributions from the Milky Way and host galaxy for localized FRBs, the $DM_{rm IGM}$ value is close to the derived $DM_{rm IGM}-z$ relation. We also show the capability to constrain the cosmic reionization history with the $DM_{rm IGM}$ of high-redshift FRBs in the IllustrisTNG universe. The derived $DM_{rm IGM}-z$ relation at high redshifts can be well fitted by a $tanh$ reionization model with the reionization redshift $z=5.95$, which is compatible with the reionization model used by the IllustrisTNG simulation. The $DM_{rm IGM}$ of high-redshift FRBs also provides an independent way to measure the optical depth of cosmic microwave background (CMB). Our result can be used to derive the pseudo-redshifts of non-localized FRBs for $DM_{rm IGM}<4000$ pc cm$^{-3}$.
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We calculate the dispersion measures (DMs) contributed by host galaxies of fast radio bursts (FRBs). Based on a few host galaxy observations, a large sample of galaxy with similar properties to observed ones has been selected from the IllustrisTNG simulation. They are used to compute the distributions of host galaxy DMs for repeating and non-repeating FRBs. For repeating FRBs, we infer the DM$ _{mathrm{host}} $ for FRBs like FRB 121102 and FRB 180916 by assuming that the burst sites are tracing the star formation rates in host galaxies. The median DM$_{mathrm{host}}$ are $35 (1+z)^{1.08}$ and $96(1+z)^{0.83}$ pc cm$^{-3}$ for FRBs like FRB 121102 and FRB 180916, respectively. In another case, the median of DM$_{mathrm{host}}$ is about $30 - 70$ pc cm$^{-3}$ for non-repeating FRBs in the redshift range $z=0.1-1.5$, assuming that the burst sites are the locations of binary neutron star mergers. In this case, the evolution of the median DM$_{mathrm{host}}$ can be calculated by $33(1+z)^{0.84}$ pc cm$^{-3}$. The distributions of DM$_{mathrm{host}}$ of repeating and non-repeating FRBs can be well fitted with the log-normal function. Our results can be used to infer redshifts of non-localized FRBs.
We analyze the sources of free electrons that produce the large dispersion measures, DM $approx 300-1600$ (in units cm$^{-3}$ pc), observed toward fast radio bursts (FRBs). Individual galaxies typically produce DM $sim 25-60$ cm$^{-3}$ pc from ionized gas in their disk, disk-halo interface, and circumgalactic medium. Toward an FRB source at redshift $z$, a homogeneous IGM containing a fraction $f_{rm IGM}$ of cosmological baryons will produce DM $= (935~{rm cm}^{-3}~{rm pc}) f_{rm IGM} , h_{70}^{-1} I(z)$, where $I(z) = (2/3 Omega_m)[ { Omega_m(1+z)^3 + Omega_{Lambda} }^{1/2} - 1 ]$. A structured IGM of photoionized Ly-alpha absorbers in the cosmic web produces similar dispersion, modeled from the observed distribution, $f_b(N,z)$, of H I (Lya-forest) absorbers in column density and redshift with ionization corrections and scaling relations from cosmological simulations. An analytic formula for DM($z$) applied to observed FRB dispersions suggests that $z_{rm FRB} approx 0.2-1.5$ for an IGM containing a significant baryon fraction, $f_{rm IGM} = 0.6pm0.1$. Future surveys of the statistical distribution, DM($z)$, of FRBs identified with specific galaxies and redshifts, can be used to calibrate the IGM baryon fraction and distribution of Ly-alpha absorbers. Fluctuations in DM at the level $pm10$ cm$^{-3}$ pc will arise from filaments and voids in the cosmic web.
We investigate the possibility of measuring intergalactic magnetic fields using the dispersion measures and rotation measures of fast radio bursts. With Bayesian methods, we produce probability density functions for values of these measures. We distinguish between contributions from the intergalactic medium, the host galaxy and the local environment of the progenitor. To this end, we use constrained, magnetohydrodynamic simulations of the local Universe to compute lines-of-sight integrals from the position of the Milky Way. In particular, we differentiate between predominantly astrophysical and primordial origins of magnetic fields in the intergalactic medium. We test different possible types of host galaxies and probe different distribution functions of fast radio burst progenitor locations inside the host galaxy. Under the assumption that fast radio bursts are produced by magnetars, we use analytic predictions to account for the contribution of the local environment. We find that less than 100 fast radio bursts from magnetars in stellar-wind environments hosted by starburst dwarf galaxies at redshift $z gtrsim 0.5$ suffice to discriminate between predominantly primordial and astrophysical origins of intergalactic magnetic fields. However, this requires the contribution of the Milky Way to be removed with a precision of $approx 1 rm~rad~m^{-2}$. We show the potential existence of a subset of fast radio bursts whose rotation measure carry information on the strength of the intergalactic magnetic field and its origins.
Fast radio bursts (FRBs) probe the total column density of free electrons in the intergalactic medium (IGM) along the path of propagation though the dispersion measures (DMs) which depend on the baryon mass fraction in the IGM, i.e., $f_{rm IGM}$. In this letter, we investigate the large-scale clustering information of DMs to study the evolution of $f_{rm IGM}$. When combining with the Planck 2018 measurements, we could give tight constraints on the evolution of $f_{rm IGM}(z)$ from about $10^4$ FRBs with the intrinsic DM scatter of $30(1+z)~ rm pc/cm^3$ spanning 80% of the sky and redshift range $z=0-3$. Firstly, we consider the Taylor expansion of $f_{rm IGM}(z)$ up to second order, and find that the mean relative standard deviation $sigma(f_{rm IGM})equivleftlangle sigma[f_{rm IGM}(z)] /f_{rm IGM}(z) rightrangle$ is about 7.2%. In order to alleviate the dependence on fiducial model, we also adopt a non-parametric methods in this work, the local principle component analysis. We obtain the consistent, but weaker constraints on the evolution of $f_{rm IGM}(z)$, namely the mean relative standard deviation $sigma(f_{rm IGM})$ is 24.2%. With the forthcoming surveys, this could be a complimentary method to investigate the baryon mass fraction in the IGM.
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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