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Register a new userThe effect of neutrinos on the matter distribution as probed by the Intergalactic Medium
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We present a suite of full hydrodynamical cosmological simulations that quantitatively address the impact of neutrinos on the (mildly non-linear) spatial distribution of matter and in particular on the neutral hydrogen distribution in the Intergalactic Medium (IGM), which is responsible for the intervening Lyman-alpha absorption in quasar spectra. The free-streaming of neutrinos results in a (non-linear) scale-dependent suppression of power spectrum of the total matter distribution at scales probed by Lyman-alpha forest data which is larger than the linear theory prediction by about 25% and strongly redshift dependent. By extracting a set of realistic mock quasar spectra, we quantify the effect of neutrinos on the flux probability distribution function and flux power spectrum. The differences in the matter power spectra translate into a ~2.5% (5%) difference in the flux power spectrum for neutrino masses with Sigma m_{ u} = 0.3 eV (0.6 eV). This rather small effect is difficult to detect from present Lyman-alpha forest data and nearly perfectly degenerate with the overall amplitude of the matter power spectrum as characterised by sigma_8. If the results of the numerical simulations are normalized to have the same sigma_8 in the initial conditions, then neutrinos produce a smaller suppression in the flux power of about 3% (5%) for Sigma m_{ u} = 0.6$ eV (1.2 eV) when compared to a simulation without neutrinos. We present constraints on neutrino masses using the Sloan Digital Sky Survey flux power spectrum alone and find an upper limit of Sigma m_{ u} < 0.9$ eV (2 sigma C.L.), comparable to constraints obtained from the cosmic microwave background data or other large scale structure probes.
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During reionization, the intergalactic medium is heated impulsively by supersonic ionization fronts (I-fronts). The peak gas temperatures behind the I-fronts, $T_mathrm{reion}$, are a key uncertainty in models of the thermal history after reionization. Here we use high-resolution radiative transfer simulations to study the parameter space of $T_mathrm{reion}$. We show that $T_mathrm{reion}$ is only mildly sensitive to the spectrum of incident radiation over most of the parameter space, with temperatures set primarily by I-front speeds. We also explore what current models of reionization predict for $T_mathrm{reion}$ by measuring I-front speeds in cosmological radiative transfer simulations. We find that the post-I-front temperatures evolve toward hotter values as reionization progresses. Temperatures of $T_mathrm{reion} = 17,000-22,000$ K are typical during the first half of reionization, but $T_mathrm{reion} = 25,000 - 30,000$ K may be achieved near the end of this process if I-front speeds reach $sim10^4$ km/s as found in our simulations. Shorter reionization epochs lead to hotter $T_mathrm{reion}$. We discuss implications for $z>5$ Ly$alpha$ forest observations, which potentially include sight lines through hot, recently reionized patches of the Universe. Interpolation tables from our parameter space study are made publicly available, along with a simple fit for the dependence of $T_mathrm{reion}$ on the I-front speed.
Upcoming measurements of the highly redshifted 21cm line with next-generation radio telescopes such as HERA and SKA will provide the intriguing opportunity to probe dark matter (DM) physics during the Epoch of Reionization (EoR), Cosmic Dawn, and the Dark Ages. With HERA already under construction, there is a pressing need to thoroughly understand the impact of DM physics on the intergalactic medium (IGM) during these epochs. We present first results of a hydrodynamic simulation suite with $2 times 512^3$ particles in a $(100 h^{-1} text{Mpc})^3$ box with DM annihilation and baryonic cooling physics. We focus on redshift $z sim 11$, just before reionization starts in our simulations, and discuss the imprint of DM annihilation on the IGM and on structure formation. We find that whereas structure formation is not affected by thermal WIMPs heavier than $m_chi gtrsim 100 text{MeV}$, heating from $mathcal{O}$(GeV) DM particles may leave a significant imprint on the IGM that alters the 21cm signal. Cold gas in low density regions is particularly susceptible to the effects of DM heating. We note, however, that delayed energy deposition is not currently accounted for in our simulations.
We study supernova-driven galactic outflows as a mechanism for injecting turbulence in the intergalactic medium (IGM) far from galaxies. To this aim we follow the evolution of a 10^13 Msun galaxy along its merger tree, with carefully calibrated prescriptions for star formation and wind efficiencies. At z~3 the majority of the bubbles around galaxies are old (ages >1Gyr), i.e. they contain metals expelled by their progenitors at earlier times; their filling factor increases with time reaching about 10% at z<2. The energy deposited by these expanding shocks in the IGM is predominantly in kinetic form (mean energy density of 1 mu eV cm^-3, about 2-3 x the thermal one), which is rapidly converted in disordered motions by instabilities, finally resulting in a fully developed turbulent spectrum whose evolution is followed through a spectral transfer function approach. The derived mean IGM turbulent Doppler parameter, b_t, peaks at z~1 at about 1.5 km/s with maximum b_t = 25 km/s. The shape of the b_t distribution does not significantly evolve with redshift but undergoes a continuous shift towards lower b_t values with time, as a result of bubble aging. We find also a clear trend of decreasing b_t with N_HI and a more complex dependence on R_s resulting from the age spread of the bubbles. We have attempted a preliminary comparison with the data, hampered by the scarcity of the latter and by the challenge provided by the subtraction of peculiar and thermal motions. Finally we comment on the implications of turbulence for various cosmological studies.
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.
Very recently a new inversion method has been developped to analyze the intergalactic medium seen in absorption in quasar spectra (the so-called Lyman-alpha forest). This method is applied to recover the temperature of the gas and the underlying density field. Using constraints from the Lyman-beta forest, it is possible to recover this field up to over-densities delta=10. By inverting the HI and CIV absorptions together it has been shown that the CIV/HI ratio varies through the profile of strong lines, beeing larger in the wings. The method can be applied to reconstruct the 3D density field from multiple lines of sight and is shown to give good results up to mean separations of 3 arcmin. Results from a survey of QSO pairs performed with HST/STIS and VLT/UVES-FORS are summarized.
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