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Register a new userReconstruction of Baryon Fraction in Intergalactic Medium through Dispersion Measurements of Fast Radio Bursts
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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.
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In this paper, we study the evolution of the ionization fraction $x_e(z)$ during the epoch of reionization by using the dispersion measurements (DMs) of fast radio bursts (FRBs). Different from the previous studies, here we turn to consider the large-scale clustering information of observed DMs of FRB catalog, which only needs the rough redshift distribution, instead of the exact redshift information of each FRB. Firstly, we consider the instantaneous ``texttt{tanh} model for $x_e(z)$ and find that including the auto-correlation information of the mock catalog, about $10^4$ FRBs with the intrinsic DM scatter of 100 $rm pc/cm^3$ spanning 20% of all sky, could significantly improve the constraint on the width $Delta_z$ of the model, when comparing with that from the CMB data alone. The evolution shape of the ionization fraction will be tightly narrowed, namely the duration of the epoch of reionization has been shrunk, $z_{rm dur}<2.24$ (95% C.L.). Furthermore, we also use another redshift-asymmetric reionization model and obtain that the FRB mock catalog could measure the ionization fraction at $z=6$ precisely with the $1sigma$ error $Delta x_e(z=6)=0.012$, which means that the large-scale clustering information of observed DMs of FRB catalog is very sensitive to the ionization fraction of the end of reionization epoch. We conclude that the observation of high-redshift FRBs could be a complementary probe to study the reionization history in the future.
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.
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$^{-3}$.
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.
Five fast radio bursts (FRBs), including three apparently non-repeating ones FRB 180924, FRB 181112, and FRB 190523, and two repeaters, FRB 121102 and FRB 180916.J0158+65, have already been localized so far. We apply a method developed recently by us (Li et al. 2019) to these five localized FRBs to give a cosmology-insensitive estimate of the fraction of baryon mass in the IGM, $f_{rm IGM}$. Using the measured dispersion measure (DM) and luminosity distance $d_{rm L}$ data (inferred from the FRB redshifts and $d_{rm L}$ of type Ia supernovae at the same redshifts) of the five FRBs, we constrain the local $f_{rm IGM} = 0.84^{+0.16}_{-0.22}$ with no evidence of redshift dependence. This cosmology-insensitive estimate of $f_{rm IGM}$ from FRB observations is in excellent agreement with previous constraints using other probes. Moreover, using the three apparently non-repeating FRBs only we get a little looser but consistent result $f_{rm IGM} = 0.74^{+0.24}_{-0.18}$. In these two cases, reasonable estimations for the host galaxy DM contribution (${rm DM_{host}}$) can be achieved by modelling it as a function of star formation rate. The constraints on both $f_{rm IGM}$ and ${rm DM_{host}}$ are expected to be significantly improved with the rapid progress in localizing FRBs.
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