共查询到20条相似文献,搜索用时 15 毫秒
1.
Jian-Sheng Chen 《Astrophysics and Space Science》1986,118(1-2):473-486
Some techniques and selection effects in establishing uniform samples of absorption line systems are presented. Summaries of the basic properties of various absorbers are given. Finally, attention is paid to some special, interesting problems which are now widely discussed.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984. 相似文献
2.
《Chinese Astronomy and Astrophysics》1983,7(1):38-41
We have made statistical analyses of current data on the absorption line redshifts of quasars. All our results, including the distribution of relative velocities and the power-spectrum of the redshift distribution of absorption systems, are in favour of the cosmological hypothesis of the origin of the quasar absorption lines. We point out that the peaks in the relative velocity distribution are no compelling evidence for the rival, intrinsic hypothesis because they can be well explained by the model of density perturbation in the early universe [10]. 相似文献
3.
Indications on clustering features in the two-point correlation function of Ly α line separations in published high-resolution spectra of quasars are presented. They are in contradiction to the self-similar hierarchical clustering model, but they could be explained by a first generation of small-scale pancakes in a model with unstable dark matter. A characteristic scale of velocity dispersion Δv ≈ 150 km/s of absorption clouds within pancakes is described by corresponding coherent regions of positive correlation, while the structure adjacent on the lines of sight are separated by a comoving distance of (18 ± 6) Mpc (H0 = 50 km/s Mpc). The appropriate coherence length of the fluctuation spectrum may result from the free streaming length of (unstable) neutrinos of (100 … 200) eV rest mass. 相似文献
4.
Pushpa Khare 《Journal of Astrophysics and Astronomy》1997,18(4):257-261
I summarize the properties of the QSO absorption lines which provide evidence for the standard model of the Universe. 相似文献
5.
M.T. Murphy J.K. Webb V.V. Flambaum J.X. Prochaska A.M. Wolfe 《Monthly notices of the Royal Astronomical Society》2001,327(4):1237-1243
Comparison of quasar (QSO) absorption-line spectra with laboratory spectra provides a precise probe for variability of the fine-structure constant, α , over cosmological time-scales. We constrain variation in α in 21 Keck/HIRES Si iv absorption systems using the alkali-doublet (AD) method in which changes in α are related to changes in the doublet spacing. The precision obtained with the AD method has been increased by a factor of 3: . We also analyse potential systematic errors in this result. Finally, we compare the AD method with the many-multiplet method, which has achieved an order of magnitude greater precision, and we discuss the future of the AD method. 相似文献
6.
M.T. Murphy J.K. Webb V.V. Flambaum C.W. Churchill J.X. Prochaska 《Monthly notices of the Royal Astronomical Society》2001,327(4):1223-1236
Comparison of quasar (QSO) absorption spectra with laboratory spectra allows us to probe possible variations in the fundamental constants over cosmological time-scales. In a companion paper we present an analysis of Keck/HIRES spectra and report possible evidence suggesting that the fine-structure constant, α , may have been smaller in the past: over the redshift range . In this paper we describe a comprehensive investigation into possible systematic effects. Most of these do not significantly influence our results. When we correct for those which do produce a significant systematic effect in the data, the deviation of from zero becomes more significant. We are led increasingly to the interpretation that α was slightly smaller in the past. 相似文献
7.
A. I. Ryabinkov A. D. Kaminker † D. A. Varshalovich 《Monthly notices of the Royal Astronomical Society》2007,376(4):1838-1848
A statistical analysis of the space–time distribution of absorption-line systems (ALSs) observed in QSO spectra within the cosmological redshift interval z = 0.0–3.7 is carried out on the base of our catalogue of absorption systems ( Ryabinkov et al. 2003 ). We confirm our previous conclusion that the z -distribution of absorbing matter contains non-uniform component displaying a pattern of statistically significant alternating maxima (peaks) and minima (dips). Using the wavelet transformation, we determine the positions of the maxima and minima and estimate their statistical significance. The positions of the maxima and minima of the z -distributions obtained for different celestial hemispheres turn out to be weakly sensitive to orientations of the hemispheres. The data reveal a regularity (quasi-periodicity) of the sequence of the peaks and dips with respect to some rescaling functions of z . The same periodicity was found for the one-dimensional correlation function calculated for the sample of the ALSs under investigation. We assume the existence of a regular structure in the distribution of absorption matter, which is not only spatial but also temporal in nature with characteristic time varying within the interval 150–650 Myr for the cosmological model applied. 相似文献
8.
Possible evidence for a variable fine-structure constant from QSO absorption lines: motivations, analysis and results 总被引:2,自引:0,他引:2
M.T. Murphy J.K. Webb V.V. Flambaum V.A. Dzuba C.W. Churchill J.X. Prochaska J.D. Barrow A.M. Wolfe 《Monthly notices of the Royal Astronomical Society》2001,327(4):1208-1222
9.
Tom Theuns H. J. Mo Joop Schaye 《Monthly notices of the Royal Astronomical Society》2001,321(3):450-462
Models for the formation of galaxies and clusters of galaxies require strong feedback in order to explain the observed properties of these systems. We investigate whether such feedback has observational consequences for the intergalactic medium, as probed in absorption towards background quasars. A typical quasar sight-line intersects one protocluster per unit redshift, and significant feedback from forming galaxies or active galactic nuclei, heating the protocluster gas, will result in a large clearing of reduced absorption in the Ly α forest. Such a gap could be detected at redshift ≳3 when the mean opacity is high. Feedback from Lyman-break galaxies in protoclusters can be probed by the absorption lines produced in their winds. Strong feedback from galaxies has a major impact on the number and properties of absorption lines with column densities N H i ∼1016 cm−2 . This feedback can be probed with multiple sight-lines and by studying the unsaturated higher order lines of the Lyman series. Galactic winds from dwarf galaxies should break up into clouds, in order not to overproduce the number of absorption lines. These clouds can then coast to large distances. 相似文献
10.
M.T. Murphy J.K. Webb V.V. Flambaum M.J. Drinkwater F. Combes T. Wiklind 《Monthly notices of the Royal Astronomical Society》2001,327(4):1244-1248
Quasar (QSO) absorption spectra provide an extremely useful probe of possible cosmological variation in various physical constants. Comparison of H i 21-cm absorption with corresponding molecular (rotational) absorption spectra allows us to constrain variation in , where α is the fine-structure constant and g p is the proton g -factor. We analyse spectra of two QSOs, PKS 1413+135 and TXS 0218+357, and derive values of at absorption redshifts of and 0.6847 by simultaneous fitting of the H i 21-cm and molecular lines. We find and respectively, indicating an insignificantly smaller y in the past. We compare our results with other constraints from the same two QSOs given recently by Drinkwater et al. and Carilli et al., and with our recent optical constraints, which indicated a smaller α at higher redshifts. 相似文献
11.
A detailed statistical analysis was carried out for several quasars with multiple red-shifts systems. The most important results are (a) The statistical test of the reliability of az-system is very sensitive toz, the total number of absorption lines, the selected set of reference lines and the number of identified lines (b) The standard deviation from , the average number of randomz-systems per random spectra is larger than . Consequently, the reliability of any system depends predominately on and not on . 相似文献
12.
S. Gallerani T. Roy Choudhury A. Ferrara 《Monthly notices of the Royal Astronomical Society》2006,370(3):1401-1421
13.
D. Basu 《Astrophysics and Space Science》1983,92(2):425-427
Search lines used for identification of observed spectral lines in QSOs and hence for determination of redshifts have significant effects on the peaks and valleys in the emission and absorption redshift distributions of the present sample of QSOs, including ‘the 1.95 peak’. 相似文献
14.
Scott M. Croom Gordon T. Richards Tom Shanks Brian J. Boyle Robert G. Sharp Joss Bland-Hawthorn Terry Bridges Robert J. Brunner Russell Cannon Daniel Carson Kuenley Chiu Matthew Colless Warrick Couch Roberto De Propris Michael J. Drinkwater Alastair Edge Stephen Fine Jon Loveday Lance Miller Adam D. Myers Robert C. Nichol Phil Outram Kevin Pimbblet Isaac Roseboom Nicholas Ross Donald P. Schneider Allyn Smith Chris Stoughton Michael A. Strauss David Wake 《Monthly notices of the Royal Astronomical Society》2009,392(1):19-44
We present the final spectroscopic QSO catalogue from the 2dF-SDSS LRG (luminous red galaxy) and QSO (2SLAQ) survey. This is a deep, 18 < g < 21.85 (extinction corrected), sample aimed at probing in detail the faint end of the broad line active galactic nuclei luminosity distribution at z ≲ 2.6 . The candidate QSOs were selected from SDSS photometry and observed spectroscopically with the 2dF spectrograph on the Anglo-Australian Telescope. This sample covers an area of 191.9 deg2 and contains new spectra of 16 326 objects, of which 8764 are QSOs and 7623 are newly discovered [the remainder were previously identified by the 2dF QSO Redshift Survey (2QZ) and SDSS]. The full QSO sample (including objects previously observed in the SDSS and 2QZ surveys) contains 12 702 QSOs. The new 2SLAQ spectroscopic data set also contains 2343 Galactic stars, including 362 white dwarfs, and 2924 narrow emission-line galaxies with a median redshift of z = 0.22 .
We present detailed completeness estimates for the survey, based on modelling of QSO colours, including host-galaxy contributions. This calculation shows that at g ≃ 21.85 QSO colours are significantly affected by the presence of a host galaxy up to redshift z ∼ 1 in the SDSS ugriz bands. In particular, we see a significant reddening of the objects in g − i towards the fainter g -band magnitudes. This reddening is consistent with the QSO host galaxies being dominated by a stellar population of age at least 2–3 Gyr.
The full catalogue, including completeness estimates, is available on-line at http://www.2slaq.info/ . 相似文献
We present detailed completeness estimates for the survey, based on modelling of QSO colours, including host-galaxy contributions. This calculation shows that at g ≃ 21.85 QSO colours are significantly affected by the presence of a host galaxy up to redshift z ∼ 1 in the SDSS ugriz bands. In particular, we see a significant reddening of the objects in g − i towards the fainter g -band magnitudes. This reddening is consistent with the QSO host galaxies being dominated by a stellar population of age at least 2–3 Gyr.
The full catalogue, including completeness estimates, is available on-line at http://www.2slaq.info/ . 相似文献
15.
The spatial-temporal distribution of absorption-line systems (ALSs) observed in QSO spectra within the cosmological redshift
interval z=0.0–4.3 is investigated on the base of our updated catalog of absorption systems. We consider so-called metallic systems
including basically lines of heavy elements. The sample of the data displays regular variations (with amplitudes ∼15–20%)
in the z-distribution of ALSs as well as in the η-distribution, where η is a dimensionless line-of-sight comoving distance, relatively to smoother dependences. The η-distribution reveals the periodicity with period Δη=0.036±0.002, which corresponds to a spatial characteristic scale (108±6)h
−1 Mpc or (alternatively) a temporal interval (350±20)h
−1 Myr for the ΛCDM cosmological model. We discuss the possibility of a spatial interpretation of the results, treating the
pattern obtained as a trace of an order imprinted on the galaxy clustering in the early Universe. 相似文献
16.
D. L. Band L. A. Ford J. L. Matteson D. M. Palmer B. J. Teegarden M. S. Briggs G. N. Pendleton R. D. Preece W. S. Paciesas 《Astrophysics and Space Science》1995,231(1-2):145-148
No absorption lines between 15 and 100 keV have been detected in burst spectra accumulated by BATSE. Almost 250 bursts have been inspected visually, and a computerized search has begun. Our simulations show that BATSE could indeed detect lines similar to those observed byGinga in strong bursts, and our tests of the detectors' actual capabilities demonstrate they function as understood. The apparent discrepancy between BATSE andGinga is not yet compelling, and therefore the BATSE nondetections do not invalidate theGinga detections. Nonetheless, the absence of BATSE line detections indicates a low line-occurrence frequency. 相似文献
17.
18.
19.