Influence of short-duration matter temperature perturbations on the cosmological hydrogen recombination spectrum

A perturbation in the ratio of the matter temperature to the radiation temperature in the form of a Gaussian with amplitude A and width σ (in units of the redshift z) centered at some redshift z _c is considered, with some “standard” temperature ratio obtained from a simultaneous solution of the cosmological recombination kinetics and energy equations being taken as the initial (unperturbed) one. Comparatively small (A = ± 0.01), fast (σ = 17) perturbations are shown to give rise to distinct narrow absorption (for A > 0) or emission (for A < 0) quasi-lines in each of the subordinate continua. The positions of these quasi-lines correlate with the position of the perturbation center, while their intensities are very sensitive to the perturbation amplitude. At the same time, the manifestation of the perturbation is much less clear in hydrogen lines (subordinate ones and the Ly-α line) and two-photon emission. As a result, the full perturbed spectrum is characterized by the presence of the narrow quasi-lines mentioned above and by a general decrease (for A > 0) or increase (for A < 0) in intensity with increasing wavelength.     

Local burst model of CMB temperature fluctuations: Scattering in the resonance lines of primordial hydrogen and helium

The propagation of an instantaneous burst of isotropic radiation from the time of its onset at some redshift z ₀ to the time of its detection at the present epoch (at z = 0) is considered within the framework of a flat Universe. The Thomson scattering by free electrons and the scattering in the primordial hydrogen Lα and Lβ lines and in the He I 1s2–1s2p, 1s3p (¹S–¹P*) lines are taken into account. It is shown that the relative amplitude of the spectral distortions due to the scattering in these lines at the corresponding frequencies can be a factor of 10³?10⁴ greater than the maximum possible amplitude from the scattering in the subordinate hydrogen lines considered previously (Dubrovich and Grachev 2015). In the linear approximation in optical depth, the distortion profiles in the resonance lines turn out to be purely absorption ones and depend neither on the direction nor on the distance to the burst center, in contrast to the profiles in the subordinate lines. The profiles contain jumps at frequencies corresponding to the instant the source (burst) appears at a given redshift z ₀. For example, at z ₀ = 5000 the jumps in the hydrogen Lα and Lβ lines lie at frequencies of 493 and 584 GHz, respectively, while in the above two helium lines they lie at frequencies of 855 and 930 GHz at z ₀ = 6000. The relative magnitude of the jumps ranges from 10?4 to 3 × 10?3.     

Magnetic Monopoles in the Early Universe: Pair Production

Magnetic monopoles and antimonopoles with masses M=10¹⁶ Gev and charges q=68.5e in the early universe are considered. Pair production may occur as a result of their Coulomb interaction. Some conditions for formation of such pairs are discussed. In particular, numerical simulations of three particle collisions are carried out. Probabilities for pair production are found in terms of the N-body problem.     

Propagation of a burst of radiation in an expanding and recombining universe: Thomson scattering

The propagation of an instantaneous burst of nonpolarized isotropic radiation from the time of its onset at some redshift z ₀ to the time of its recording at the present epoch is considered within the framework of a flat cosmological model. Thomson (Rayleigh) scattering by free electrons is believed to be the only source of opacity. The spatial distributions of the mean (over the directions) radiation intensity as well as the angular distributions of the radiation intensity and polarization at various distances from the burst center have been constructed. The mean intensity profile normalized to the total number of photons emitted during the burst is shown to depend weakly on the initial conditions (the burst time z ₀, the width and shape of the initial radiation distribution) at fairly high z ₀ (≥1400). As regards the angular intensity and polarization distributions, they turn out to be rather narrow (3–10 arcmin), while the polarization can reach 70%. On average, the expected polarization can be about 15%.     

Search for spatial and spectral fluctuations of the cosmic microwave background radiation using the RATAN-600 radio telescope

We report the results of a search for spatial and spectral fluctuations of the cosmic microwave background in the region of the North celestial pole carried out at 6.2 cm using the RATAN-600 radio telescope in 1999–2000. The spatial spectrum is flat and has no features exceeding ΔT/T =10^?3 in a ～1 MHz frequency band for spatial periods from 0.5′ to 16′. If this estimate is adopted as an upper limit for emission associated with the first rotational transition of primordial LiH at z=90.7, we obtain an upper limit for the LiH abundance of about 3×10^?14 for protocluster masses of about 10¹³ M _⊙.     

Local burst model of CMB temperature fluctuations: scattering in primordial hydrogen lines

The propagation of an instantaneous burst of isotropic radiation from the time of its onset at some redshift z ₀ to the time of its detection at the present epoch (at z = 0) is considered within the framework of a flat Universe. Thomson scattering by free electrons and scattering in primordial hydrogen lines (Hα, Hβ, Pα, and Pβ) are believed to be the sources of opacity, with the single-scattering albedo in the lines being calculated by taking into account the deexcitation of the upper levels of the transitions being considered under the action of background blackbody radiation. The profiles of these lines in the burst spectrum at the present epoch have been constructed for various z0 at various distances from the burst center. To a first approximation, these profiles do not depend on the burst radiation spectrum and intensity. It is shown that the lines are purely absorption ones at a sufficiently large distance, but an emission component can appear with decreasing distance, which strengthens as the distance decreases, while the absorption component weakens. The absorption depth in the combined profile can reach 2 ×10^?4 for the Hα and Hβ lines and 7 × 10^?6 for the Pα and Pβ lines. In this case, the relative amplitude of the temperature fluctuations lies within the range 10^?7?10^?9. The calculations have been performed for bursts with different characteristic initial sizes. At the same z ₀, the hydrogen line profiles essentially coincide for sizes smaller than some value, and the contrast of the lines decreases with increasing burst size for greater ones.

     

Primordial hydrogen recombination dynamics with recoil upon scattering in the Ly-<Emphasis Type="Italic">α</Emphasis> line

We show that including the recoil upon scattering in the Ly-α line can lead to a noticeable acceleration of the primordial hydrogen recombination. Thus, for example, for the ΛCDM model, the decrease in the degree of ionization exceeds 1% at redshifts z = 800–1050, reaching ≈1.3% at z = 900. The corresponding corrections to the calculated cosmic microwave background power spectra reach 1.1% and 1.7% for TT and EE spectra, respectively. The radiative transfer in these calculations was treated in the quasi-stationary approximation.We have also obtained numerical solutions (in the diffusion approximation) to the nonstationary problem of radiative transfer in the Ly-α line for a partial frequency redistribution with recoil. We trace the evolution of the local line profile and the relative number of uncompensated transitions from the 2p state to the 1s state. We show that including the nonstationarity of the Ly-α line radiative transfer can lead to an additional acceleration of the primordial hydrogen recombination.     

Polarization of Cosmic Microwave Backgdound Scattered by Moving Flat Protoobjects

The work is devoted to the investigations of possible observational manifestations of protoobjects related to the dark ages epoch (10 < z < 1000), before formation of self-luminous galaxies and stars. These objects can distort the cosmic microwave background. Formation of these objects is described in the pancake theory and in the model of hierarchic clustering. According to these theories we may consider these protoobjects as flat layers. We consider both Thomson (with Rayleigh phase matrix) and resonance (for complete frequency redistribution) scattering of cosmic microwave background radiation by a moving flat layer. The resulting anisotropy and polarization of cosmic microwave radiation are calculated for a wide range of layer optical thickness (from an optically thin layer to an optically thick one). Analytical solutions are also obtained for the case of an optically thin layer and are compared with the numerical ones.     

Hydrogen recombination in an expanding universe

Leningrad State University; Special Astrophysical Observatory, USSR Academy of Sciences. Translated from Astrofizika, Vol. 34, No. 2, pp. 249–264, March–April, 1991.     

Formation mechanisms of “Negative”-intensity spots in the cosmic microwave background radiation and distant objects

We consider the formation mechanisms of “negative”-intensity spots in the radio band for various astrophysical conditions. For wavelengths λ<1.5 mm, the regions of reduced temperature (relative to the cosmic microwave background radiation, CMBR) are shown to be produced only by high-redshift objects moving at peculiar velocities. The main processes are CMBR Thomson scattering and bremsstrahlung. We show that the effect δT/T can be ～10^?5 in magnitude. We derive simple analytic expressions, which allow the redshifts, electron densities, and linear sizes of these regions to be estimated from observed spectral and spatial parameters. Additional observational methods for refining these parameters are outlined.