A statistical study of the Lyman-Alpha absorption lines of nine quasars

We investigate the properties of the Lα absorption lines in the high resolution spectra of nine quasars, B2 1225+31.7, PKS 2126-158, Q 0002-422, Q 1453-423, PHL 957, PKS 0528-250, PKS 0805+046, PKS 1448-232 and PKS 1442+101. Their emission line redshift range is 2.20 ? z_em ? 3.54; a total of 350 Lα absorption lines cover the range 1.70 ? z_abs ? 3.54. Our analysis support the following conclusions; 1) the number density of Lα absorption lines is not significantly different in different quasars. 2) The number density does not vary significantly with redshift. 3) Their equivalent width spectrum does not vary significantly with redshift. 4) Their properties are the same whether in the wing of the Lα emission or in the continuum. 5) Their two-point correlation function is flat within the limit of resolution, which is different from the behaviour of galaxies. These results show that the Lα absorption lines in high-redshift quasars are very probably produced by intergalactic hydrogen clouds uniformly distributed throughout space.     

A new examination of absorption line density in the Lα forest of QSOs

The distribution of the absorption lines in the L forest of QSOs is re-examined in relation to both absorption and emission redshifts by analyzing a sample consisting of 20 QSO L forests.On the one hand, the -value in the relationN(z _abs)=N ₀(1+z _abs) is re-estimated by applying the maximum likelihood (ML) method to all the L forests in our sample as a whole as well as to the forests for individual QSOs. The global estimated is 2.20±0.28 and both the quasars with highest and lowestz _em do not individually have a significant effect on it. A non-parametric test on the estimate of from individual QSOs shows that there is no significant difference between the numbers of positive and negative -values. This does not, therefore, favour the idea that for individual QSOsN(z _abs) decreases with increasingz _abs.On the other hand, the possible correlation between the absorption line density and the emission redshift of the QSO itself, which was found by Bianet al. (1986, 1988) and re-discovered independently by Tytler (1987), is shown once again not only by the largerz _em QSOs having larger mean density, but more importantly, at a rather high confidence level, by the fact that, at the same values ofz _abs, QSOs with largerz _em possess a greater number of L absorption lines.A discussion of the inverse effect suggests that it is still hard to say whether this effect really exists.     

Integral field observations of damped Lyman‐α galaxies

We report preliminary results from a targeted investigation on quasars containing damped Lyman‐α absorption (DLA) lines as well strong metal absorption lines, carried out with the Potsdam Multi Aperture Spectrophotometer (PMAS). We search for line‐emitting objects at the same redshift as the absorption lines and close to the line of sight of the QSOs. We have observed and detected the already confirmed absorbing galaxies in Q2233+131 (z_abs = 3.15) and Q0151+045 (z_abs=0.168), while failing to find spectral signatures for the z = 0.091 absorber in Q0738+313. From the Q2233+131 DLA galaxy, we have detected extended Lyα emission from an area of 3″ ×5″. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

QSOs as probes of the early universe

The spectrum of the highest redshift QSO 2000–330 (z=3.78) contains four heavy-element absorption systems withz _abs>3.0. Interesting features include velocity structure atz _abs=3.552 which suggests a cluster origin and a purely low ionization system atz _abs=3.1881 typical of a galactic disk sightline.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Redshift difference between emission and absorption lines of QSOs

Distribution of the redshift difference (z) between emission and absorption lines of QSOs is half-gaussian. Also, the quantity z increases with increase in emission line redshift (z _em). The correlation between the two quantities (z andz _em) is statistically significant. The interpretation of the results indicate that the co-moving density of absorbing clouds decreases with redshift and that the absorbing clouds are associated with the QSOs rather than completely unrelated intervening material.     

HD molecular lines in an absorption system at redshift z=2.3377

Having analyzed the spectrum of the quasar PKS 1232+0.82 taken by Petitjean et al. (2000), we identified HD molecular lines in an absorption system at redshift z=2.3377. We estimated the column density of HD molecules in this system, N(HD) = (1?4) × 10¹⁴cm^?2. The excitation temperature of the first rotational level J=1 relative to the ground state J=0 is T _ex=70 ± 7 K. As far as we know, this is the first detection of HD molecules at high redshift.     

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.     

Galaxy redshift abundance periodicity from Fourier analysis of number counts N(z) using SDSS and 2dF GRS galaxy surveys

A Fourier analysis on galaxy number counts from redshift data of both the Sloan Digital Sky Survey and the 2dF Galaxy Redshift Survey indicates that galaxies have preferred periodic redshift spacings of Δz= 0.0102, 0.0246, and 0.0448 in the SDSS and strong agreement with the results from the 2dF GRS. The redshift spacings are confirmed by the mass density fluctuations, the power spectrum P(z) and N _pairs calculations. Application of the Hubble law results in galaxies preferentially located on co-moving concentric shells with periodic spacings. The combined results from both surveys indicate regular co-moving radial distance spacings of 31.7±1.8 h^?1?Mpc, 73.4±5.8 h^?1?Mpc and 127±21 h^?1? Mpc. The results are consistent with oscillations in the expansion rate of the universe over past epochs.     

Associated HI absorption in thez = 3.4 radio galaxy B2 0902 + 343 observed with the GMRT

We have made observations of the as sociated HI absorption of a high redshift radio galaxy 0902+34 atz = 3.395 with the Giant Meterwave Radio Telescope in the 323 ± 1 MHz band. We find a narrow absorption line with a flux density of 11.5 mJy at a redshift of 3.397 consistent with that observed by Usonet al. (1991), Briggset al. (1993) and de Bruyn (1996). A weak broad absorption feature reported by de Bruyn (1996) has not been detected in our observations. We also place an upper limit of 4mJy(2σ) on emission line strength at the position where Usonet al. (1991) claimed to have found a narrow emission line.     

Molecular Hydrogen in high redshift Damped Lyman-α systems

I describe briefly the status of an ongoing mini-survey for molecular hydrogen in high-redshift Damped Lyman-α systems using UVES at the VLT. H₂ is detected in about 30% of the cases. When H2 is not detected the molecular fraction f = 2N(H₂)/(2N(H₂)+N(HI) is smaller than 10^-5. Therefore, most of the DLA systems arise in warm (T > 3000 K) and diffuse neutral gas embedded in a strong UV flux. The very recent detection of HD molecules in a Damped Lyman-α system at z _abs = 2.337 demonstrates the possibility to discuss the high redshift chemistry. This revised version was published online in September 2006 with corrections to the Cover Date.     

类星体L_α森林吸收线密度与发射红移的相关性

本文对16个高红移类星体的L_α森林吸收线密度N(z_(abs))统计分析的结果,表明它明显地依赖于类星体自身的发射红移z_(em)。这不仅表现在z(em)越大的类星体其全部L_α吸收线的平均数密度N(z_(abs))也越大;更重要的是,对于相同的吸收红移值z_(abs),而言,N(z_(abs))在统计意义上明显地随着类星体z_(em)的增大而增大。另一方面,本文也在“吸收体源自类星体抛射”的框架下作了统计,结果仍表明z_(em)对L_α森林吸收线密度有显著影响,但抛射速度却对被抛射体的数目无显著影响。最后,对所得的结果以及可能影响N(z_(abs))的若干因素作了讨论。     

Absorption features of QSOs

Absorption features shown by QSOs may be identified and measured as reported absorption redshift systems, or may remain unidentified and not measured. The features are believed to be observed in objects with high emission redshifts (z _em), although no quantitative analysis exists to examine any such preferential trend, except that by Basu (1982). However, redshift data have since increased enormously both in range of the redshift spectrum and in number. Furthermore, the earlier analysis was based on only the reported absorption redshifts while unidentified absorption features were not dealt with. The present paper analyses the updated data, both identified and unidentified features. It is found that absorption features may be expressed as exponential function ofz _em, and upper limits are set for the percentage of QSOs showing absorption features. Finally, an entirely new method of analysis confirms the earlier conclusion of Basu (1982) that the appearance of absorbing clouds is closely associated with the creation of the QSOs, the two may be having a common cause. It is suggested that absorption QSOs may be a separate class of QSOs whose birth is accompanied with creation of absorbing clouds.     

Optical identification of the hard X-ray source IGR J18257-0707

We present the results of our optical identification of the hard X-ray source IGR J18257-0707 through its spectrophotometric observations with the optical RTT-150 telescope. The accurate position of the X-ray source determined using Chandra observations has allowed this source to be confidently associatedwith a faint optical object (m _R ≈ 20.4) whose optical spectrumexhibits a broad H _α emission line at redshift z = 0.037. Thus, the source IGR J18257-0707 is a type-1 Seyfert galaxy at redshift z = 0.037.     

Om diagnostic for viscous Cardassian universe

Om diagnostic is a useful geometric method to differentiate between different cosmological models without the accurate current value of matter density. We investigate the Om diagnostic for viscous Cardassian universe and find that the model can be easily distinguished from LCDM. We also investigate the influence of the bulk viscosity coefficient τ on the evolutive behavior of Om with respect to redshift z. According to the value of Om(z=0) for viscous Cardassian models, we obtain the current value of equation of state w _k0.     

The Unusual Absorption Line Spectrum of Quasar SDSS J2220+0109

We report the Balmer broad absorption lines (BALs) in the quasar SDSS J2220 + 0109 discovered from the SDSS data, and present a detailed analysis of the peculiar absorption line spectrum, including the He I* multiplet at λλ3189, 3889 arising from the metastable 2³s-state helium and the Balmer Hα and Hβ lines from the excited hydrogen H I of n = 2 level, which are rarely seen in quasar spectra, as well as many absorption lines arising from the excited Fe II* of the levels 7 955 cm⁻¹, 13 474 cm⁻¹ and 13 673 cm⁻¹ in the wavelength range 3100∼3300 Å. Ca II H, K absorption line doublets also clearly appear in the SDSS spectrum. All absorption lines show a similar blueshifted velocity structure of Δv ≈ − 1500 ∼ 0 km·s⁻¹ relative to the quasar's systematic redshift determined from the emission lines. Detailed analysis suggests that the Balmer absorption lines should arise from the partially ionized region with a column density of N_HI ≈ 10²¹ cm⁻² for an electron density of ne ∼ 10⁶ cm⁻³; and that the hydrogen n = 2 level may be populated via collisional excitation with Lyα pumping.     

Determination of the mean H<Emphasis Type="SmallCaps">i</Emphasis> absorption of the intergalactic medium

In recent years, the Lyman-α forest in quasar spectra has been used, together with N-body simulations, to determine the underlying matter distribution in the intergalactic medium (IGM). One of the key parameters to be known in order to compare observations and numerical simulations is the mean HI absorption in the IGM. To derive the latter, one has first to fit the quasar continuum. We have observed 20 high redshift and highly luminous QSOs (m _V ≤ 17.5 and 2.40 ≤ z _em ≤ 3.91) at intermediate spectral resolution, with either EMMI (ESO Multi-Mode Instrument) on the ESO-NTT telescope or CARELEC at the OHP (Observatoire de Haute-Provence), and applied different methods of determining the QSO continuum to this QSO sample. We have measured the amount of absorption, known as the flux decrement, DA, in the Lyman-α forest for these different methods and compared the results. In addition, we have compared DA values measured along the same lines of sight observed at high and intermediate spectral resolutions. We discuss the systematics resulting from the use of automatic continuum fitting methods.     

A study of the H-alpha line in late G and K supergiants

A spectroscopic study of H_α has been carried out to investigate the properties of expanding chromospheres of late G and K supergiants. Spectra of 23 stars brighter thanV = 6.0 have been obtained at dispersions of 4–10 å mm^-1 using the coude and the coudé-echelle spectrographs at the 102-cm telescope of Kavalur Observatory. The H_α profiles are all asymmetric in the sense that the absorption core is shifted to the blue by amounts ranging between -4 and -24 km s^-1. H_α profiles were theoretically computed using radiative transfer in spherically symmetric expanding atmospheres covering a large range of integrated optical depths. These were compared with the characteristics of the observed line in the programme stars. The analysis shows that the H_α line is formed in a region with velocity increasing outward. The computed equivalent widths and line core displacements were matched with those observed to obtain hydrogen column densities and expansion velocities. From these, the rates of mass loss in these stars were determined to be in the range of 10⁶10^-7 M_⊙ yr^-1.     

FRB Event Rate Predictions for the Ooty Wide Field Array

We developed a generic formalism to estimate the event rate and the redshift distribution of Fast Radio Bursts (FRBs) in our previous publication (Bera et al. 2016), considering FRBs are of an extragalactic origin. In this paper, we present (a) the predicted pulse widths of FRBs by considering two different scattering models, (b) the minimum total energy required to detect events, (c) the redshift distribution and (d) the detection rates of FRBs for the Ooty Wide Field Array (OWFA). The energy spectrum of FRBs is modelled as a power law with an exponent ?α and our analysis spans a range ?3≤α≤5. We find that OWFA will be capable of detecting FRBs with α≥0. The redshift distribution and the event rates of FRBs are estimated by assuming two different energy distribution functions; a Delta function and a Schechter luminosity function with an exponent ?2≤γ≤2. We consider an empirical scattering model based on pulsar observations (model I) as well as a theoretical model (model II) expected for the intergalactic medium. The redshift distributions peak at a particular redshift z _p for a fixed value of α, which lie in the range 0.3≤z _p ≤1 for the scattering model I and remain flat and extend up to high redshifts (z?5) for the scattering model II.     

Effects on partial prequency redistributionR II on the level population ratios in a resonance line

Angle-averaged partial frequency redistributionR II has been employed in obtaining a simultaneous solution of radiative transfer equation in the comoving frame and the statistical equilibrium equation for a non-LTE two level atom. We have obtained the ratios of population densities of the upper and lower levels of the resonance line of PV by utilizing the data given in Bernacca and Bianchi (1979). Line source functions are also obtained for different types of variations of density and velocity of the expanding gases. We have considered the atmosphere to be 11 times as thick as the stellar radius. The first iteration was started by putting the density of the upper level (N ₂) equal to zero. However, the convergent solution shows a substantial increase inN ₂ although it is still much less than the equilibrium value. The line source function and the ratio of the densities of the particles in the upper and lower levels fall sharply from a maximum at τ=τ_max to minimum at τ=0. We have studied the scattering integral \(\int {_{ - \infty }^{ + \infty } J_x \phi _x } dx\) and found that this quantity also varies quite similar to the ratioN ₂/N ₁ and the line source functionS _L.     

类星体Lα森林吸收线密度与发射红移相关性的再考察

继文[1]之后,本文利用15个中—高红移类星体的Lα森林构成统计样本,再度考察了Lα森林吸收线密度N(Z_(abs))与发射红移Z_(em)的相关性。本文的统计样本包含的红移范围比文[1]更大:类星体的发射红移值从1.715到3.750,Lα森林吸收线红移范围从1.501到3.780;统计方法亦与文[1]略有差异。统计结果再度表明,Lα森林吸收线密度N(Z_(abs))明显依赖于类星体自身的发射红移Z_(em),这不仅在于Z_(em)越大的类星体其全部吸收线的平均数密度N(Z_(abs))也越大,更重要的是,对于相同的吸收红移值Z_(abs)而言,N(Z_(abs))在统计意义上明显地随Z_(em)的增大而增大。文末对所得的结果作了讨论。