[en] Quasar spectra provide a unique opportunity to investigate the intergalactic medium at high redshifts. The spectral analysis of the Lya forest allows us to constrain the effective equation of state of the intergalactic medium and its changes during the evolution of the Universe. Based on the Voigt profile fitting of Lya forest lines in 50 high-resolution QSO spectra obtained at Keck telescope we present new measurements of the power-law index γ of temperature-density relation in IGM for six redshift bins in the range z = 1.6 – 3.7. We find that the IGM state is close to isothermal (γ ≈ 1) at z ∼ 3 which may indicate that HeII reionization occurred at this redshift. (paper)

[en] We present new measurements of HD/H₂ in absorption systems at redshift z ∼ 2 in quasar spectrum J 0812+3208 and J 2340−0053. In J 0812+3208 we detect and measure column density of H₂ at z ∼ 2.07 for the first time and place upper limit on HD column density. In J 2340−0043 we identify HD in already known multicomponent H₂ absorption system at z ∼ 2.05. In this system we obtain relative abundance of HD/H₂ molecules close to isotopic ratio, suggesting the similar molecular fraction of deuterium and hydrogen. We discuss possible explanation of measured HD/H₂ abundance. (paper)

[en] We present a simplified semi-analytical description of the relative HD/H₂ abundance in the cold neutral interstellar medium. With this description we was able to obtain three asymptotics of the relative HD/H₂ abundance and its dependence on physical parameters in the medium, namely, the number density of the gas, the intensity of the ultraviolet field, the cosmic ray ionization rate and metallicity. Our calculations in presented simple formalism are in the reasonable agreement with the calculations using the Meudon PDR code. We found that in the case of low metallicity and a higher cosmic ray ionization rate, the relative abundance of HD/H₂ is significantly enhanced, which can explain the observed difference between the local and high-z measurements of relative HD/H₂ abundance. (paper)

[en] Spectroscopy of the Lya forest in quasar spectra proved to be a useful tool for probing the intergalactic gas. We developed the automatic program for Voigt profile fitting of Lya forest lines. We run this code on 9 high resolution (∼ 50000) quasars spectra with a high signal-to-noise ratio (∼ 50 — 100) from the Keck telescope archive and obtained the sample of single well-fitted Lya lines. Fitting the joint 2d distribution of column density and Doppler parameter from this sample by physically reasonable model we estimate a power law index, γ, of the equation of state of the intergalactic medium in the redshift range z ∼ 2 — 3. We found that our measurement is in an agreement with measurements by other groups obtained with Voigt profile fitting technique. (paper)

[en] Absorption spectra of distant quasars are the main source of our knowledge of physical conditions, structures, and composition of matter in the Early Universe. The detailed analysis of such spectra gave us a possibility to discover HD/H₂ molecular clouds existed 12-13 Gyr, investigate them and derive some important cosmological conclusions.

[en] We present a new analysis of the quasar spectrum J 2123-0050 obtained using VLT/UVES. The H2/HD absorption system at z = 2.059 was analysed. This system consists of two subsystems with z_A = 2.05933 and z_B = 2.05955. The HD lines have been detected only in subsystem A with the column density of log N = 13.87 ± 0.06. We have determined the column density of H_2 in this subsystem, log N = 17.93 ± 0.01, which is about three times larger than estimation derived early from analyses of quasar spectrum obtained using KECK/HIRES [1]. The derived ratio HD/2H_2 = (4.28 ± 0.60) × 10"-"5 is the largest in quasar spectra, nevertheless it coincides with the primordial deuterium abundance within 2σ error. Additionally, we have found some evidence in the partial covering effect for the H_2 system. (paper)

[en] The linear relation between the temperature of the Cosmic Microwave Background and the cosmological redshift is a fundamental prediction of the standard hot Big Bang model. Measurements of the CMB temperature in the past can be done by means of observing radiative excitation of atomic and molecular species like C and CO. It can be detected in quasar spectra with z ∼ 2. We study excitation of CO rotational levels both by the CMB radiation and collisions. Corrections of determination of the CMB temperature due to collisional excitation by the analysis of CO molecule rotation level populations are proposed. (paper)

[en] We have estimated the probability of a partial coverage of QSO broad-line regions by intervening H₂-clouds. This effect has been revealed by an analysis of H₂ absorption systems in QSO spectra [1, 2]. Accounting of the effect may change significantly physical parameters of interstellar clouds derived from the spectral analysis [2]. We show that the probability of incomplete coverage turns out to be not lower than about 8%. Actually, a frequency of the effect revealing may occur essentially higher than this quantity, encouraging us in further systematic searches of the incomplete coverage in the H₂ absorption QSO spectra

[en] We consider the distortions of the cosmic microwave background (CMB) dipole anisotropy related to primordial recombination radiation (PRR) and primordial y- and μ-distortions. The signals arise due to our motion relative to the CMB restframe and appear as a frequency-dependent distortion of the CMB temperature dipole. To leading order, the expected relative distortion of the CMB dipole does not depend on the particular observation directions and reaches the level of 10⁻⁶ for the PRR- and μ-distortions and 10⁻⁵ for the y-distortion in the frequency range 1–700 GHz. The temperature differences arising from the dipole anisotropy of the relic CMB distortions depend on the observation directions. For mutually opposite directions, collinear to the CMB dipole axis, the temperature differences due to the PRR- and μ-dipole anisotropy attain values $\mathrm{\Delta <!--\; ??\; -->}T\simeq <!--\; ???\; -->10\mathrm{n}\mathrm{K}$ in the considered range. The temperature difference arising from the y-dipole anisotropy may reach values of up to $1\mathrm{\mu <!--\; ??\; -->}\mathrm{K}$. The key features of the considered effect are as follow: (i) an observation of the effect does not require absolute calibration; (ii) patches of sky with minimal foreground contamination can be chosen. Future measurements of the CMB dipole distortion thus will provide an alternative method for direct detection of the PRR-, y-, and μ-distortions. The y-distortion dipole may be detectable with PIXIE at a few standard deviations.

[en] We present the results of spectroscopic analysis of seven new H₂-bearing damped Ly- systems in redshift range z=2.5 − 3. These systems were originally selected from SDSS catalog using a direct search for H₂ and followed up with X-SHOOTER spectrograph at 8-m Very Large Telescope observatory. We measured the column densities of H_I, H₂ on various rotational levels, and metals species in different ionization stages and excitation levels. We used the rotational excitation of H₂ molecules together with the fine-structure levels of neutral carbon to constrain the physical conditions in the associated medium. We found typical values for the kinetic temperature T ∼ 80 − 120 K, hydrogen density n _H ∼ 30 − 400 cm⁻³ and UV radiation field ξ_UV ∼ 0.4 − 5 times of the Draine field. These values along with estimated thermal pressure are in agreement with expected values from the theoretical calculation of the cold neutral interstellar medium. (paper)