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Register a new userThe impact of population III objects on the early universe
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We study the effects of the ionizing and dissociating photons produced by Pop III objects on the surrounding intergalactic medium. We find that the typical size of a H_2 photodissociated region is smaller than the mean distance between sources at z=20-30, but larger than the ionized region. This implies that clearing of the intergalactic H_2 occurs before reionization of the universe is complete. In the same redshift range, the soft-UV background in the Lyman- Werner bands, when the intergalactic H and H_2 opacity is included, is found to be J_LW = 10^-28 - 10^-26 erg cm^-2 s^-1 Hz^-1. This value is well below the treshold required for the negative feedback of Pop III objects on the subsequent galaxy formation to be effective. We have combined these semi-analytical results with high-resolution N-body simulations, to study the topological structure of photoionization and photodissociation and the evolution of the H^+ and H_2 filling factor.
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We study the formation and destruction of molecules in the ejecta of Population III supernovae (SNe) using a chemical kinetic approach to follow the evolution of molecular abundances from day 100 to day 1000 after explosion. The chemical species included range from simple di-atomic molecules to more complex dust precursor species. All relevant chemical processes that are unique to the SN environment are considered. Our work focuses on zero-metallicity progenitors with masses of 20, 170, and 270 Msun, and we study the effect of different levels of heavy element mixing and the inward diffusion of hydrogen on the ejecta chemistry. We show that the ejecta chemistry does not reach a steady state within the relevant time-span for molecule formation. The primary species formed are O2, CO, SiS, and SO. The SiO, formed as early as 200 days after explosion, is rapidly depleted by the formation of silica molecular precursors in the ejecta. The rapid conversion of CO to C2 and its thermal fractionation at temperatures above 5000 K allow for the formation of carbon chains in the oxygen-rich zone of the unmixed models, providing an important pathway for the formation of carbon dust in hot environments where the C/O ratio is less than 1. We show that the fully-mixed ejecta of a 170 Msun progenitor synthesizes 11.3 Mun of molecules whereas 20 Msun and 270 Msun progenitors produce 0.78, and 3.2 Msun of molecules, respectively. The admixing of 10 % of hydrogen into the fully-mixed ejecta of the 170 Msun progenitor increases its molecular yield to ~ 47Msun. The unmixed ejecta of a 170 Msun progenitor supernova without hydrogen penetration synthesizes ~37 Msun of molecules, whereas its 20 Msun counterpart produces ~ 1.2 Msun. Finally, we discuss the cosmological implication of molecule formation by Pop. III SNe in the early universe.
We systematically investigated the heating of coronal loops on metal-free stars with various stellar masses and magnetic fields by magnetohydrodynamic simulations. It is found that the coronal property is dependent on the coronal magnetic field strength $B_{rm c}$ because it affects the difference of the nonlinearity of the Alfv{e}nic waves. Weaker $B_{rm c}$ leads to cooler and less dense coronae because most of the input waves dissipate in the lower atmosphere on account of the larger nonlinearity. Accordingly EUV and X-ray luminosities also correlate with $B_{rm c}$, while they are emitted in a wide range of the field strength. Finally we extend our results to evaluating the contribution from low-mass Population III coronae to the cosmic reionization. Within the limited range of our parameters on magnetic fields and loop lengths, the EUV and X-ray radiations give a weak impact on the ionization and heating of the gas at high redshifts. However, there still remains a possibility of the contribution to the reionization from energetic flares involving long magnetic loops.
In the previous parts of the discussion on the same topic, various aspects of the very early universe were discussed. We discussed how inclusion of large dark energy term compensates for the net gravity. Here the discussion is taken further including the effects of charge, magnetic fields and rotation. The role of large extra dimensions under the extreme initial conditions is discussed and possible connection with the cyclic brane theory is explored. We constrain various cosmic quantities like the net charge, number density of magnetic monopoles, primordial magnetic fields, size of the extra dimensions,etc.
We present the results of the stellar feedback from Pop III binaries by employing improved, more realistic Pop III evolutionary stellar models. To facilitate a meaningful comparison, we consider a fixed mass of 60 solar masses (Msun) incorporated in Pop III stars, either contained in a single star, or split up in binary stars of 30 Msun each or an asymmetric case of one 45 Msun and one 15 Msun star. Whereas the sizes of the resulting HII regions are comparable across all cases, the HeIII regions around binary stars are significantly smaller than that of the single star. Consequently, the He$^{+}$ 1640 angstrom recombination line is expected to become much weaker. Supernova feedback exhibits great variety due to the uncertainty in possible explosion pathways. If at least one of the component stars dies as a hypernova about ten times more energetic than conventional core-collapse supernovae, the gas inside the host minihalo is effectively blown out, chemically enriching the intergalactic medium (IGM) to an average metallicity of $10^{-4}-10^{-3}$ solar metallicity (Zsun), out to $sim 2$ kpc. The single star, however, is more likely to collapse into a black hole, accompanied by at most very weak explosions. The effectiveness of early chemical enrichment would thus be significantly reduced, in difference from the lower mass binary stars, where at least one component is likely to contribute to heavy element production and dispersal. Important new feedback physics is also introduced if close binaries can form high-mass x-ray binaries, leading to the pre-heating and -ionization of the IGM beyond the extent of the stellar HII regions.
We present new constraints on parameters of cosmic dawn and the epoch of reionization derived from the EDGES High-Band spectrum ($90-190$ MHz). The parameters are probed by evaluating global $21$ cm signals generated with the recently developed Global21cm tool. This tool uses neural networks trained and tested on $sim 30,000$ spectra produced with semi-numerical simulations that assume the standard thermal evolution of the cosmic microwave background and the intergalactic medium. From our analysis, we constrain at $68%$ (1) the minimum virial circular velocity of star-forming halos to $V_{rm c}<19.3$ km s$^{-1}$, (2) the X-ray heating efficiency of early sources to $f_{rm X}>0.0042$, and (3) the low-energy cutoff of the X-ray spectral energy distribution to $ u_{rm min}<2.3$ keV. We also constrain the star-formation efficiency ($f_*$), the electron scattering optical depth ($tau_{rm e}$), and the mean-free path of ionizing photons ($R_{rm mfp}$). We re-compute the constraints after incorporating into the analysis four estimates for the neutral hydrogen fraction from high-$z$ quasars and galaxies, and a prior on $tau_{rm e}$ from Planck $2018$. The largest impact of the external observations is on the parameters that most directly characterize reionization. Specifically, we derive the combined $68%$ constraints $tau_{rm e}<0.063$ and $R_{rm mfp}>27.5$ Mpc. The external observations also have a significant effect on $V_{rm c}$ due to its degeneracy with $tau_{rm e}$, while the constraints on $f_*$, $f_{rm X}$, and $ u_{rm min}$, remain primarily determined by EDGES.
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