arXiv subjects

S. A. Balashev

Publications and source records attributed to S. A. Balashev.

45 records · Page 3Linked to original sources

arXiv2015

Spectral distortions of the CMB dipole

We consider the distortions of the cosmic microwave background (CMB) dipole anisotropy related to the 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 because of the PRR- and $μ$-dipole anisotropy attain values $ΔT\simeq 10\,$nK in the considered range. The temperature difference arising from the $y$-dipole anisotropy may reach values of up to $1\,μ$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.

astro-ph.CO↗

arXiv2015

Neutral chlorine and molecular hydrogen at high redshift

Chlorine and molecular hydrogen are known to be tightly linked together in the cold phase of the local interstellar medium through rapid chemical reactions. We present here the first systematic study of this relation at high redshifts using H$_2$-bearing damped Ly$α$ systems (DLAs) detected along quasar lines of sight. Using high-resolution spectroscopic data from VLT/UVES and Keck/HIRES, we report the detection of Cl$\,$I in 9 DLAs (including 5 new detections) out of 18 high-$z$ DLAs with $N($H$_2) \ge 10^{17.3}\,$cm$^{-2}$ (including a new H$_2$ detection at $z=3.09145$ towards J$\,$2100$-$0641) and present upper limits for the remaining 9 systems. We find a $\sim$5$\,σ$ correlation between $N$(Cl$\,$I) and $N$(H$_2$) with only $\sim$0.2$\,$dex dispersion over the range 18.1$\,<\,$log$\,N$(H$_2$)$\,<\,$20.1, thus probing column densities 10 times lower those seen towards nearby stars, roughly following the relation $N$(Cl$\,$I$) \approx 1.5\times10^{-6} \times N($H$_2)$. This relation between column densities is surprisingly the same at low and high redshift suggesting that the physical and chemical conditions are similar for a given H$_2$ (or Cl$\,$I) column density. In turn, the $N({Cl$\,$I})/N({\rm H_2})$ ratio is found to be uncorrelated with the overall metallicity in the DLA. Our results confirm that neutral chlorine is an excellent tracer of molecule-rich gas and show that the molecular fraction or/and metallicity in the H$_2$-bearing component of DLA could possibly be much higher than the line-of-sight average values usually measured in DLAs.

astro-ph.GA↗

arXiv2015

Partial covering of emission regions of Q 0528-250 by intervening H$_2$ clouds

We present an analysis of the molecular hydrogen absorption system at z$_{\rm abs}$ = 2.811 in the spectrum of the blazar Q0528-250. We demonstrate that the molecular cloud does not cover the background source completely. The partial coverage reveals itself as a residual flux in the bottom of saturated H_2 absorption lines. This amounts to about (2.22$\pm$0.54)% of the continuum and does not depend on the wavelength. This value is small and it explains why this effect has not been detected in previous studies of this quasar spectrum. However, it is robustly detected and significantly higher than the zero flux level in the bottom of saturated lines of the Ly-alpha forest, (-0.21$\pm$0.22)%. The presence of the residual flux could be caused by unresolved quasar multicomponents, by light scattered by dust, and/or by jet-cloud interaction. The H$_2$ absorption system is very well described by a two-component model without inclusion of additional components when we take partial coverage into account. The derived total column densities in the H$_2$ absorption components A and B are logN(H$_2$)[cm$^{-2}$] = 18.10$\pm$0.02 and 17.82$\pm$0.02, respectively. HD molecules are present only in component B. Given the column density, logN(HD)= 13.33$\pm$0.02, we find N(HD)/2N(H$_2$)=(1.48$\pm$0.10)x10$^{-5}$, significantly lower than previous estimations. We argue that it is crucial to take into account partial coverage effects for any analysis of H$_2$ bearing absorption systems, in particular when studying the physical state of high-redshift interstellar medium.

astro-ph.GA↗

arXiv2014

Molecular hydrogen absorption systems in Sloan Digital Sky Survey

We present a systematic search for molecular hydrogen absorption systems at high redshift in quasar spectra from the Sloan Digital Sky Survey (SDSS) II Data Release 7 and SDSS-III Data Release 9. We have selected candidates using a modified profile fitting technique taking into account that the Ly$α$ forest can effectively mimic H$_2$ absorption systems at the resolution of SDSS data. To estimate the confidence level of the detections, we use two methods: a Monte-Carlo sampling and an analysis of control samples. The analysis of control samples allows us to define regions of the spectral quality parameter space where H$_2$ absorption systems can be confidently identified. We find that H$_2$ absorption systems with column densities $\log {\rm N_{H_2}} > 19$ can be detected in only less than 3% of SDSS quasar spectra. We estimate the upper limit on the detection rate of saturated H$_2$ absorption systems ($\log {\rm N_{H_2}} > 19$) in Damped Ly-$α$ (DLA) systems to be about 7%. We provide a sample of 23 confident H$_2$ absorption system candidates that would be interesting to follow up with high resolution spectrographs. There is a 1$σ$ $r-i$ color excess and non-significant $A_{\rm V}$ extinction excess in quasar spectra with an H$_2$ candidate compared to standard DLA-bearing quasar spectra. The equivalent widths (EWs) of C II, Si II and Al III (but not Fe II) absorptions associated with H$_2$ candidate DLAs are larger compared to standard DLAs. This is probably related to a larger spread in velocity of the absorption lines in the H$_2$ bearing sample.

astro-ph.CO↗

arXiv2014

The Thermal Sunyaev-Zeldovich Effect of Primordial Recombination Radiation

It is well known that recombination radiation of primordial hydrogen-helium plasma leads to the distortions of the planckian spectrum shape of the cosmic microwave background radiation (CMB). We discuss the thermal Sunyaev-Zeldovich (SZ) effect with taking into account primordial recombination radiation (PRR). Since in the thermal SZ effect the redistribution of the photons depends on the derivatives of the spectrum, the value of relative correction to SZ effect due to PRR significantly higher than relative corrections due to PRR in the initial spectrum. Calculations of corrections to the thermal SZ effect due to PRR show that depending on the cluster parameters: 1) in the range of frequencies $ν$ = 0.3 - 700 GHz where the cosmic microwave background (CMB) dominates and spectrum is very close to the planckian one the relative corrections due to PRR have an order of $10^{-9} - 10^{-6}$ of "pure" SZ effect (i.e. SZ effect for pure planckian spectrum). The difference of intensities of PRR coming from different directions (through intracluster and near intercluster medium) reaches values up to 22 mJy/ster at $ν\simeq 337$ GHz (maximum in considered range). 2) In the range of frequencies $ν$ = 700 - 5000 GHz where cosmic infrared background (CIB) becomes significant or even dominates the relative corrections due to PRR can reach $10^{-8}$ - $10^{-5}$ of "pure" SZ effect. Corresponding intensity difference reaches values up to 25 mJy/ster (at $ν\simeq 1700$ GHz). In addition we suggest a modification of the method of electron gas temperature determination using corrections of the SZ effect due to PRR. Such modification allows one to simplify the determination of the cluster electron gas temperature in comparison with known methods.

astro-ph.CO↗

arXiv2011

Partial coverage of the Broad Line Region of Q1232+082 by an intervening H2-bearing cloud

We present a detailed analysis of the partial coverage of the Q1232+082 (z_em =2.57) broad line region by an intervening H_2-bearing cloud at z_abs=2.3377. Using curve of growth analysis and line profile fitting, we demonstrate that the H_2-bearing component of the cloud covers the QSO intrinsic continuum source completely but only part of the Broad Line Region (BLR). We find that only 48\pm6 % of the C IV BLR emission is covered by the C I absorbing gas. We observe residual light (~6 %) as well in the bottom of the O I λ1302 absorption from the cloud, redshifted on top of the QSO Lyman-α emission line. Therefore the extent of the neutral phase of the absorbing cloud is not large enough to cover all of the background source. The most likely explanation for this partial coverage is the small size of the intervening cloud, which is comparable to the BLR size. We estimate the number densities in the cloud: n_H2~110 cm^{-3} for the H_2-bearing core and n_H ~30 cm^{-3} for the neutral envelope. Given the column densities, N(H2)=(3.71\pm0.97)\times10^19 cm^{-2} and N(H I)=(7.94\pm1.6)\times10^20 cm^{-2}, we derive the linear size of the H_2-bearing core and the neutral envelope along the line of sight to be l_H2~0.15^{+0.05}_{-0.05} pc and l_HI~8.2^{+6.5}_{-4.1} pc, respectively. We estimate the size of the C IV BLR by two ways (i) extrapolating size-luminosity relations derived from reverberation observations and (ii) assuming that the H_2-bearing core and the BLR are spherical in shape and the results are ~0.26 and ~0.18 pc, respectively. The large size we derive for the extent of the neutral phase of the absorbing cloud together with a covering factor of ~0.94 of the Lyman-α emission means that the Lyman-α BLR is probably fully covered but that the Lyman-α emission extends well beyond the limits of the BLR.

astro-ph.CO↗

arXiv2010

HD/H2 Molecular Clouds in the Early Universe: The Problem of Primordial Deuterium

We have detected new HD absorption systems at high redshifts, z_abs=2.626 and z_abs=1.777, identified in the spectra of the quasars J0812+3208 and Q1331+170, respectively. Each of these systems consists of two subsystems. The HD column densities have been determined: log(N(HD),A)=15.70+/-0.07 for z_A=2.626443(2) and log(N(HD),B)=12.98+/-0.22 for z_B=2.626276(2) in the spectrum of J0812+3208 and log(N(HD),C)=14.83+/-0.15 for z_C=1.77637(2) and log(N(HD),D)=14.61+/-0.20 for z_D=1.77670(3) in the spectrum of Q1331+170. The measured HD/H2 ratio for three of these subsystems has been found to be considerably higher than its values typical of clouds in our Galaxy. We discuss the problem of determining the primordial deuterium abundance, which is most sensitive to the baryon density of the Universe Ω_{b}. Using a well-known model for the chemistry of a molecular cloud, we have estimated the isotopic ratio D/H=HD/2H_2=(2.97+/-0.55)x10^{-5} and the corresponding baryon density Ω_{b}h^2=0.0205^{+0.0025}_{-0.0020}. This value is in good agreement with Ω_{b}h^2=0.0226^{+0.0006}_{-0.0006} obtained by analyzing the cosmic microwave background radiation anisotropy. However, in high-redshift clouds, under conditions of low metallicity and low dust content, hydrogen may be incompletely molecularized even in the case of self-shielding. In this situation, the HD/2H_2 ratio may not correspond to the actual D/H isotopic ratio. We have estimated the cloud molecularization dynamics and the influence of cosmological evolutionary effects on it.

astro-ph.CO↗

arXiv2010

HD molecules at high redshift: The absorption system at z=2.3377 towards Q 1232+082

We present a detailed analysis of the H_2 and HD absorption lines detected in the Damped Lyman-alpha (DLA) system at z_abs=2.3377 towards the quasar Q1232+082. We show that this intervening cloud has a covering factor smaller than unity and covers only part of the QSO broad emission line region. The zero flux level has to be corrected at the position of the saturated H_2 and optically thin HD lines by about 10%. We accurately determine the Doppler parameter for HD and CI lines (b = 1.86+/-0.20 km/s). We find a ratio N(HD)/N(H_2)=(7.1 +3.7 -2.2)x10^-5 that is significantly higher than what is observed in molecular clouds of the Galaxy. Chemical models suggest that in the physical conditions prevailing in the central part of molecular clouds, deuterium and hydrogen are mostly in their molecular forms. Assuming this is true, we derive D/H = (3.6 +1.9 -1.1)x10^-5. This implies that the corresponding baryon density of the Universe is Ω_b h^2 = (0.0182 +0.0047 -0.0042). This value coincides within 1σwith that derived from observations of the CMBR as well as from observations of the D/H atomic ratio in low-metallicity QSO absorption line systems. The observation of HD at high redshift is therefore a promising independent method to constrain Ω_b. This observation indicates as well a low astration factor of deuterium. This can be interpreted as the consequence of an intense infall of primordial gas onto the associated galaxy.

astro-ph.CO↗

arXiv2009

Directional Radiation and Photodissociation Regions in Molecular Hydrogen Clouds

Some astrophysical observations of molecular hydrogen point to a broadening of the velocity distribution for molecules at excited rotational levels. This effect is observed in both Galactic and high redshift clouds. Analysis of H_2, HD, and CI absorption lines has revealed the broadening effect in the absorption system of QSO 1232+082 (z_{abs}=2.33771). We analyze line broadening mechanisms by considering in detail the transfer of ultraviolet radiation (in the resonance lines of the Lyman and Werner H_2 molecular bands) for various velocity distributions at excited rotational levels. The mechanism we suggest includes the saturation of the lines that populate excited rotational levels (radiative pumping) and manifests itself most clearly in the case of directional radiation in the medium. Based on the calculated structure of a molecular hydrogen cloud in rotational level populations, we have considered an additional mechanism that takes into account the presence of a photodissociation region. Note that disregarding the broadening effects we investigated can lead to a significant systematic error when the data are processed.

astro-ph.CO↗