Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userIntergalactic medium heating by dark matter
50
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We derive the evolution of the energy deposition in the intergalactic medium (IGM) by dark matter (DM) decays/annihilations for both sterile neutrinos and light dark matter (LDM) particles. At z > 200 sterile neutrinos transfer a fraction f_abs~0.5 of their rest mass energy into the IGM; at lower redshifts this fraction becomes <~ 0.3 depending on the particle mass. The LDM particles can decay or annihilate. In both cases f_abs~0.4-0.9 at high (> 300) redshift, dropping to ~0.1 below z=100. These results indicate that the impact of DM decays/annihilations on the IGM thermal and ionization history is less important than previously thought. We find that sterile neutrinos (LDM) decays are able to increase the IGM temperature by z=5 at most up to 4K (100K), about 50-200 times less than predicted by estimates based on the assumption of complete energy transfer to the gas.
rate research
Read More
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.
The preheating of intergalactic medium(IGM) by structure collapsing and ultraviolet background(UVB) are investigated in cosmological hydrodynamical simulations. When gravitational collapsing is the sole heating mechanism, we find that (1) $60%, 45%$ of the IGM are heated up to $S>8, 17$ kev cm$^2$ respectively at $z=0$, but the fractions drop rapidly to a few percents at $z=2$, (2) the entropy of the circum-halo gas $S_{rm{cir}}$ is higher than the virial entropy for more than $75 %$ of the halos with masses $M<10^{11.5}$ $M_{odot}$ since $z=2$, but the fraction higher than the entropy, $S_{rm{pr}}$, required in preventive model of galaxies formation is only $15-20 %$ for halos with $M<10^{10.5} M_{odot}$ at $z=0$, and decreases as redshift increases, (3)assuming a metallicity of $Z leq 0.03 Z_{odot}$, the fraction of halos whose circum-halo gas having a cooling time longer than the Hubble time $t_{cool,cir}>t_{rm{H}}$ is merely $5-10 %$ at $z lesssim 0.5$, and even less at $z geq 1$ for halos with $M<10^{10.5} M_{odot}$. (4) gas in the filaments undergoes the strongest preheating. Furthermore, we show that the UVB can not enhance the fraction of IGM with $S>17$ kev cm$^2$, but can increase the fraction of low mass halos($<10^{10.5} M_{odot}$) that having $S_{rm{cir}}>S_{rm{pr}}$ to $sim 70 %$ at $z=0$, and that having $t_{rm{cool, cir}}>t_{rm{H}}$ to $15-30 %$ at $z lesssim 0.5$. Our results indicate that preheating due to gravitational collapsing and UVB are inadequate to fulfil the needs of preventative model, especially for halos with $10^{10.5}<M<10^{11.5} M_{odot}$. Nevertheless, these two mechanisms might cause large scale galactic conformity.
The intergalactic medium is expected to be at its coldest point before the formation of the first stars in the universe. Motivated by recent results from the EDGES experiment, we revisit the standard calculation of the kinetic temperature of the neutral gas through this period. When the first ultraviolet (UV) sources turn on, photons redshift into the Lyman lines of neutral hydrogen and repeatedly scatter within the Lyman-$alpha$ line. They heat the gas via atomic recoils, and, through the Wouthuysen-Field effect, set the spin temperature of the 21-cm hyperfine (spin-flip) line of atomic hydrogen in competition with the resonant cosmic microwave background (CMB) photons. We show that the Lyman-$alpha$ photons also mediate energy transfer between the CMB photons and the thermal motions of the hydrogen atoms. In the absence of X-ray heating, this new mechanism is the major correction to the temperature of the adiabatically cooling gas ($sim 10 %$ at $z=17$), and is several times the size of the heating rate found in previous calculations. We also find that the effect is more dramatic in non-standard scenarios that either enhance the radio background above the CMB or invoke new physics to cool the gas in order to explain the EDGES results. The coupling with the radio background can reduce the depth of the 21-cm absorption feature by almost a factor of two relative to the case with no sources of heating, and prevent the feature from developing a flattened bottom. As an inevitable consequence of the UV background that generates the absorption feature, this heating should be accounted for in any theoretical prediction.
The intergalactic medium (IGM) prior to the epoch of reionization consists mostly of neutral hydrogen gas. Ly-alpha photons produced by early stars resonantly scatter off hydrogen atoms, causing energy exchange between the radiation field and the gas. This interaction results in moderate heating of the gas due to the recoil of the atoms upon scattering, which is of great interest for future studies of the pre-reionization IGM in the HI 21 cm line. We investigate the effect of this Ly-alpha heating in the IGM with linear density, temperature, and velocity perturbations. Perturbations smaller than the diffusion length of photons could be damped due to heat conduction by Ly-alpha photons. The scale at which damping occurs and the strength of this effect depend on various properties of the gas, the flux of Ly-alpha photons and the way in which photon frequencies are redistributed upon scattering. To find the relevant length scale and the extent to which Ly-alpha heating affects perturbations, we calculate the gas heating rates by numerically solving linearized Boltzmann equations in which scattering is treated by the Fokker-Planck approximation. We find that (1) perturbations add a small correction to the gas heating rate, and (2) the damping of temperature perturbations occurs at scales with comoving wavenumber k>10^4 Mpc^{-1}, which are much smaller than the Jeans scale and thus unlikely to substantially affect the observed 21 cm signal.
Dark matter (DM) decays and annihilations might heat and partially reionize the Universe at high redshift. Although this effect is not important for the cosmic reionization, the gas heating due to DM particles might affect the structure formation. In particular, the critical halo mass for collapse is increased up to a factor of ~2. Also the fraction of gas which collapses inside the smallest halos is substantially reduced with respect to the cosmological value. These effects imply that DM decays and annihilations might delay the formation of the first structures and reduce the total star mass in the smallest halos.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
