Variation in the Opacity of the Intergalactic Medium During its Reionization

It is now assumed that reionization of the intergalactic medium occurred under the action of ultraviolet radiation from hot stars contained in galaxies that formed early. Regions of ionized hydrogen (H II zones) were formed around such galaxies. The effects of hydrogen recombination and of the simultaneous cosmological expansion of such regions on their opacity are considered. It is shown that regions formed at z _i < 6 are opaque to L _c radiation, while for z _i 5 the intergalactic medium should be transparent at 0 < z < 5. This conclusion is in accord with recent observational data.     

The galactic diffuse component of soft X-rays and its source function

A new model for the source distribution of galactic soft X-ray (B and C band) emission is presented. From the mean dependence of count rates on galactic latitudeb (i.e., the brightness distribution), we derive the soft X-ray source functionQ as function of the optical depth by solving the equation of radiative transfer with the aid of a Laplace transform. Contrary to older Heaviside step models,Q is found to increase strongly, but not abruptly, in the range 1.5<<2.5, indicating a noticeable emission of X-rays from beyond theHi scale height. Using standard X-ray absorption cross-sections for the interstellar medium, we find that the B band X-ray emission coefficient is non-zero within theHi disk and has a maximum at az-value slightly above the Hi scale height. In the C band, the emission coefficient slightly decreases with increasingz, at least up to theHi scale height. A non-zero source function near the galactic plane implies that the interstellar medium (ISM) within theHi scale height is not only an absorbing layer but is mixed with X-ray emitting regions. The so-called local hot bubble is adopted as one of these regions. The maximum of the B band emission coefficient, together with the sharp increase ofQ, is strong evidence for the existence of a galactic soft X-ray halo, and, moreover, give rise to the assumption of a general intergalactic X-ray background. The effective absorption cross-sections given in the literature, based on an (pure) exponential dependence in the negative correlation between count rates andHi column densities, were biased to be too small, in particular in the B band. In replacing the Heaviside step (in the ISM) by a smoothed transition region, these inconsistencies become spurious.     

Spektrum und Anisotropiegrad der 3 °K-Strahlung bei anisotroper kosmologischer Expansion

Two theorems concerning the propagation of electromagnetic radiation which interacts with matter through elastic electron scattering in arbitrary gravitational fields allow to draw conclusions relevant to the thermal history of the 3 °K microwave background: Provided, a thermalization at some instant t = t₁ in the past has established at this time a Planckian photon distribution function (possibly with the temperature T depending on the propagation direction and on space coordinates), then (i) the Planckian distribution is preserved in a first approximation, if the deviation of the actual distribution from an isotropic Planckian remains always small; and (ii) in the Rayleigh-Jeans domain the Planckian shape is preserved independent of the degree of radiation anisotropy. Due to thermalizing action of electron scattering in ionized intergalactic and pre-galactic matter the observed degree of anisotropy in the 3 °K microwave background may be smaller as is expected for collisionless radiation propagating in a given geometry. To study this effect, the equation of radiative transfer with an electron scattering term is integrated in an anisotropic universe of the Heckmann-Schücking type (Bianchi type I), starting from an early optically thick epoch (corresponding to a radiation temperature T = 5000 °K) prior to plasma recombination. With the quadrupole anisotropy of the order of 2 · 10⁻³ found by Partridge and Wilkinson in the Rayleigh-Jeans domain, metric anisotropy parameters ranging from a = 380 to 900 years are derived, if the re-ionization of intergalactic matter sets in at redshift values ranging from z_r = 0 to z_r = 8.     

Preheating of the early universe by radiation from high-mass X-ray binaries

Using a reliablymeasured intrinsic (i.e., corrected for absorption effects) present-day luminosity function of high-mass X-ray binaries (HMXBs) in the 0.25–2 keV energy band per unit star formation rate, we estimate the preheating of the early Universe by soft X-rays from such systems. We find that X-ray irradiation, mainly executed by ultraluminous and supersoft ultraluminous X-ray sources with luminosity L _X > 10³⁹ erg s^?1, could significantly heat (T >T _CMB, where T _CMB is the temperature of the cosmic microwave background) the intergalactic medium by z ~ 10 if the specific X-ray emissivity of the young stellar population in the early Universe was an order of magnitude higher than at the present epoch (which is possible due to the low metallicity of the first galaxies) and the soft X-ray emission from HMXBs did not suffer strong absorption within their galaxies. This makes it possible to observe the 21 cm line of neutral hydrogen in emission from redshifts z < 10.     

A possibility to useCi infrared absorption lines for determination of the background radiation temperature at earlier cosmological epochs

A method for the determination of the background radiation temperature in earlier cosmological epochs at redshiftsz>2 is discussed in detail. The method is based on the fact that in the clouds situated at cosmological distances at redshiftz the background radiation temperature must be (1+z) times more than in the modern epoch (z=0). This shall affect the level populations of the atoms, ions and molecules and, consequently, the parameters of the absorption lines observed in quasar absorption spectra. It is proposed to use the transition³ P ₀–³ P ₁ ofCi (=610 ) for the measurement of the background radiation temperature. Atz>2 this absorption line shifts to the millimeter radio region and can be observed by radioastronomical methods.     

Primeval galaxies: Predicted luminosities

Absorption by gas and dust in circumstellar Hii regions within primeval galaxies could seriously depress the far-ultraviolet continuum radiation emitted by primeval galaxies. This effect might account for the failure of Partridge (1974) and Davis and Wilkinson (1974) to detect the redshifted radiation from primeval galaxies at optical and near-infrared wavelengths. A primeval galaxy becomes very bright only during the final stages of contraction. Provided that dust can form by the time the primeval galaxy reaches peak luminosity, a significant fraction of the stellar far-ultraviolet radiation is converted into far-infrared. Thus an appropriate spectral region to search for the redshifted integrated background from primeval galaxies lies between 350 , where the 2.7 K microwave background radiation becomes important, and 150 , where other extragalactic discrete sources, such as nearby galactic nuclei, may contribute. The expected IR flux is calculated with Kaufman's (1975) model for the star formation rate in the contracting galaxy. Letz _p be the redshift andT _g the grain temperature when the primeval galaxy becomes very bright. Unlessz _p10 orT _g is fairly high, the intensity of the far-infrared radiation from primeval galaxies would be dominated by the high frequency tail of the 2.7 K microwave background. On the other hand, if dust is unimportant, we determine the spectral energy distribution of a primeval galaxy emitted in the range 912 Å to 2050 Å; we find that the luminosities are not very sensitive to the dependence of effective temperatures on metal abundance.     

Small-scale anisotropy of microwave background radiation computed by means of the transfer function betweenz=2000 andz=800

We use the transfer function betweenz=2000 andz=800, to compute the small-scale anisotropy of the microwave background radiation (MBR). Then the numerical input is minimized and most physical effects are computed on analytical bases. The different slopes of the spectrum are used to account for different mass scales. The numerical results show that the dependence of T/T on the spectrum indexn is not monotonic but rather different for the two regimes ofn<2 andn>2: forn<2 the curves with largern will be higher than that with smallern, while forn>2 the curves with largern will go down. The highest curve corresponds ton=2.     

Intergalactic extinction and the deceleration parameter

The deceleration parameter q₀ is calculated from the relation between apparent magnitudes m of the brightest galaxies in clusters and their redshifts z considering an intergalactic extinction. The calculation is valid for a Friedman universe, homogeneously filled with dust grains, assuming the extinction to be 0.5 mag at z = 1 and a λ⁻¹-law of extinction (according to Oleak and Schmidt 1976). Using the m,z-values of Kristian, Sandage, and Westphal (1978) a formal value of q₀ ≈︁ 2.1 is obtained instead of q₀ ≈︁ 1.6 without consideration of intergalactic extinction.     

Pulsars and interstellar medium: Multiple regression analysis of related parameters

An empirical relation which relates the 408 MHz galactic continuum background temperature (408GCBT) to dispersion measures, position and radio-luminosity of 325 pulsars is obtained by means of multple stepwise regression analysis. This relation showns that pulsars may be considered as galactic probes for the distribution of 408GCBT and interstellar electron density (IED) in interstellar medium (ISM).Peculiar pulsars (O-C±2.5) point out galactic regions where the observedT ₄₀₈ are higher (or lower) andn _e lower (or higher) than the averaged ones.Normal pulsars (–2.5T ₄₀₈ andn _e are in agreement, on, the average.Standard pulsars (O-C±0.05) show galactic regions where observed and computedT ₄₀₈ andn _e are in good agreement. Recent models of pulsar disk systems, suggested by Michel and Dessler (1981) could justify the conclusions drawn for peculiar pulsars having O-C>2.5.     

On the possibility of using metal unblanketed model atmospheres for analysis of population II stars

A comparison between model atmosphere grids with and without metal blanketing has been performed in the low-temperature range (T _eff=6000 K to 10000 K) and for different metal contents (logA=0, –1, –2;A=scaled solar abundance). ForA10^–1 andT _eff7000 K, the Johnson colour indicesU-B andB-V, together with the Strömgrenu-b, b-y and the bolometric correction (BC) are little affected by metal blanketing ( mag<0 _. ^m 04). On the other hand, the trend of the physical quantities and them ₁ andc ₁ colour indices reflect the inadequateness of the models even withA=10^–2 andT _eff=9500 K, where hydrogen line blanketing is expected to dominate. This fact discourages once and for all the use of metal unblanketed atmospheres other than for comparison of colour indices or the calculation of bolometric corrections for Population II A-F spectral types.     

On the existence and the density of intergalactic dust

A relation between the redshift z of QSO's and their colour index (B–V)' corrected for line emission and galactic absorption is interpreted in terms of an intergalactic selective extinction. The observed amount of extinction corresponds to a density of intergalactic dust grains of about 10⁻³⁴ to 10⁻³³ g cm⁻³ at z = 0. The life-time of these particles are estimated to be longer than the Hubble -time at present. But at large z the life-time of the grains considerably depends on the flux density of cosmic rays. Some implications of the existence of intergalactic dust are discussed.     

Motion of rigid bodies in a set of redundant variables

In this article we study the conditions for obtaining canonical transformationsy=f(x) of the phase space, wherey(y ₁,y ₂,...,y _2n ) andx(x ₁,x ₂,...,x _2m ) in such a way that the number of variables is increased. In particular, this study is applied to the rotational motion in functions of the Eulerian parameters (q ₀,q ₁,q ₂,q ₃) and their conjugate momenta (Q ₀,Q ₁,Q ₂,Q ₃) or in functions of complex variables (z ₁,z ₂,z ₃,z ₄) and their conjugate momenta (Z ₁,Z ₂,Z ₃,Z ₄) defined by means of the previous variables. Finally, our article include some properties on the rotational motion of a rigid body moving about a fixed point.     

An electron temperature distribution derived from optical and radio measurements of HII regions

Radio measurements of the electron temperature ofHii regions are obtained from the ratio of the brightness temperature of a hydrogen recombination line to that of the adjacent continuum, while optical measurements are obtained from the ratio of [Oiii] forbidden-line intensities. The radio and optical measurements made under the assumption of an isothermalHii region,T _R andT _opt respectively, are combined to derive a temperature distribution for an entire nebula. A sphericalHii region in local thermodynamic equilibrium with constant density which is optically thin in both the line and the continuum is used as a model. Assuming linear temperature gradients withT _R=6000K andT _opt=10000K, it is found thatT=12000K (1–0.74r/R), wherer is the distance from the center andR is the radius of the nebula.     

Distribution of gaps in emission line redshifts of QSOs

A gap in the distribution of a parameter is simply the absence of the parameter for the values corresponding to the gap. The gap in the emission line redshift (z) of QSOs thus represents absence of QSOs with emission line redshift values corresponding to the gap region. Gaps in emission line redshifts of QSOs have been analysed statistically with updated data consisting of 1549 values. The study indicates: (i) There is a critical redshiftz _c =2.4, which separates two distinct phases in the creation of QSOs. Forz>z _c , the creation appears to have been a slow process. Atz?z _c there was a triggering action which produced a burst of QSOs simultaneously. Forz _c , the rate of production of QSOs have been fast. (ii) The distribution of gaps atz _c ; appear to be consequence of periodicities, provided the periodicities involved are perfect and the redshift values are accurate. (iii) The distribution of gaps atz>z _c are not random, but follow a definite trend.     

Two‐dimension potentials which generate spatial families of orbits

We consider the following case of the 3D inverse problem of dynamics: Given a spatial two‐parametric family of curves f (x, y, z) = c₁, g (x, y, z) = c₂, find possibly existing two‐dimension potentials under whose action the curves of the family are trajectories for a unit mass particle. First we establish the conditions which must be fulfilled by the family so that potentials of the form w (y, z) give rise to the curves of the family, and we present some applications. Then we examine briefly the existence of potentials depending on (x, z), respectively (x, y), which are compatible with the given family (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of intergalactic dust on the measurement of the cosmological deceleration parameterq 0

In a recent attempt to explain the cosmic microwave background without the big bang, a thermalization mechanism involving intergalactic whisker grains of graphite was proposed. The effect of absorption by the intergalactic medium in general, and of the above type in particular, on the measurement of the deceleration parameterq ₀ of the expanding universe is discussed. Its effect is shown to be comparable in magnitude but opposite to that of the luminosity evolution in galaxies. A consequential selection effect is also discussed.     

Investigation of non-uniform heating during the decay phase of solar flares

We have analysed X-ray spectra of 13 solar flares as obtained by the Bent Crystal Spectrometer (BCS) on the Solar Maximum Mission. In particular, we have examined the observed ratio of T _Fe/T _Ca where T _Fe and T _Ca are the temperatures obtained from the Fexxv and Caxix spectra, respectively. In order to simplify the investigation we have analysed only flares which reach quasi-steady-state during the decay. It turned out that the observed ratios cannot be explained by a model consisting of a single, uniformly heated loop, with a constant or variable cross-sectional area. We propose that this problem may be solved by introducing some distribution of the heating function across the flaring loop. This model has been tested by detailed calculations.     

Programmed motion in the presence of homogeneity

In the framework of the inverse problem of dynamics, we face the following question with reference to the motion of one material point: Given a region T_orb of the xy plane, described by the inequality g (x, y) ≤ c₀, are there potentials V = V (x, y) which can produce monoparametric families of orbits f (x, y) = c (also to be found) lying exclusively in the region T_orb? As the relevant PDEs are nonlinear, an answer to this question (generally affirmative, but not with assurance) can be given by the procedure of the determination of certain constants specifying the pertinent functions. In this paper we ease the mathematics involved by making certain simplifying assumptions referring to the homogeneity of both the function g (x, y) (describing the boundary of T_orb) and of the slope function γ(x, y) = f_y/f_x (representing the required family f (x, y) = c). We develop the method to treat the so formulated problem and we show that, even under these restrictive assumptions, an affirmative answer is guaranteed provided that two algebraic equations have in common at least one solution (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure of X-ray irradiated stellar wind

The effect of X-ray irradiation on the line-driven stellar wind in X-ray binary systems is studied. The product of the X-ray luminosityL _x and the densityn in the wind is a measure to distinguish between the optically thin and thick wind regimes. For an X-ray source of the radiation temperature of 10 keV, the critical value(L _x n) _c , is of the order of 10³⁷ erg s^–1 cm^–3; hence, most of wind-fed X-ray sources lie in the optically thick wind regime because ofL _x n>(L _x n) _c . Then the wind structure is determined not only by the parameter =(L _x /nR ²),R the distance from the X-ray source, but also by the optical thickness due to helium. The formation of fully ionized helium region depends onL _x andn in a way different from that of the Strömgren sphere. In such an optically thick wind, the region behind the He II ionization boundary is little affected by X-ray irradiation and the trace elements remain to be responsible for wind acceleration. Thus, its location is important for the structure of the wind and the interpretation of various phenomena in objects such as wind-fed X-ray pulsars.     

X-ray absorption effects due to intergalactic abundance of carbon

The absorption effects at the soft X-ray and hard ultraviolet wavelengths due to some model abundance of intergalactic carbon material have been investigated for different cosmologies. Even though the local density, 2 × 10⁹ <ϱ ₀ = 1.0 × 10⁻³⁴ g cm⁻³ of the absorbing component of the intergalactic material in the form of carbon is not adequate for the thermalization of the discrete background radiation, the amount of absorption in the X-rays up to the Hubble radius is not negligible.