共查询到20条相似文献,搜索用时 9 毫秒
1.
This paper is the second one of a series of papers on the redshift distribution of QSOs. In this paper, we shall study the influence of the selection effect in the identification of emission lines on the redshift distribution of QSOs more thoroughly than the previous paper (Zhouet al., 1983). If we assume that the QSO's redshift is cosmological, adopt the standard model, and consider the selection effect due to the redshift identification, the limiting apparent magnitude in the observation and the evolutionary effect of QSOs, we can compute the emission line redshift distribution for the so-called optically selected QSOs discovered by objective prism, grating prism technique alone, the QSOs discovered by positional methods or by colour technique and for whole QSOs, respectively (see Figures 6, 11, 12). The results of computation agree with the observations very well, especially for optically selected QSOs; the computational distribution has almost the same shape with the observational one. For this kind of the QSOs the computational distribution may give the positions and heights of all these observed peaks. The correlation coefficient between the calculated and observed distributions is larger than 0.95. It shows that (a) the peaks and dips in the redshift distribution of QSOs are mainly caused by the selection effect in the redshift identification, and (b) the redshift of QSOs is cosmological. 相似文献
2.
D. Basu 《Astrophysics and Space Science》1980,70(2):527-529
A gap in a distribution is the interval between two consecutive values. Analysis of gaps in the absorption line redshift distribution (241 values) of QSOs shows a definite trend in the distribution of gaps. The trend indicates that the absorption line distribution is not random, but does not suggest any periodicity. 相似文献
3.
D. Basu 《Astrophysics and Space Science》1977,47(2):315-318
A gap in a distribution is the interval between two consecutive values. Gaps in the emission line redshift distribution of QSOs are analysed using up-to-date data comprising 371 objects. It is found that the distribution of gaps is not random, but follows a definite trend, depending on the mean value of the redshift in the region. 相似文献
4.
D. Basu 《Astronomische Nachrichten》2001,322(4):229-231
Periodicities and selection effects in the redshift (z) distribution of QSOs have been debated for a long time in the literature. Here we show that peaks and troughs in the redshift distribution of three new samples, claimed to demonstrate the existence of a periodicity, can be interpreted in terms of known selection effects. This analysis confirms earlier findings that the presence of such selection effects seriously weakens any suggestion for periodicity of the form Δl n (1 + z) = constant. 相似文献
5.
D. Basu 《Astronomische Nachrichten》1987,308(5):299-301
Strong emission lines may change the brightness of QSOs and hence their observed magnitudes. Since different lines will affect the magnitudes by entering a particular filter at different redshifts, this effect may alter the number of QSOs at a particular redshift and hence the redshift distribution. The present analysis shows that the influence of the emission lines on the U and B magnitudes are significantly correlated to the redshift distribution. It is concluded that the changes in observed magnitudes of QSOs caused by the emission lines have significant effects on the present redshift distribution. 相似文献
6.
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
7.
D. Basu 《Astrophysics and Space Science》1983,94(2):463-468
The peak in the distribution of apparent magnitude (V) of QSOs at 18.0 can be explained by loss of QSOs forV<-18.0 arising out of selection effects due to the availability of search lines necessary for the determination of redshifts and due to the misidentification of QSOs as Main-Sequence stars. ForV>18.0, the number of objects seem to fall off as they become progressively fainter and detection efficiency goes down. The present analysis also shows that a strong correlation exists between apparent magnitude and redshift of QSOs indicating redshifts are of cosmological origin. 相似文献
8.
9.
D. Basu 《Astrophysics and Space Science》1980,72(1):241-245
In this Letter we report the findings of a statistically significant relation between the continuum color indices and redshift of optically violent variable QSOs. No such correlation is found to exist for non-variable and moderately variable QSOs. 相似文献
10.
D. Basu 《Astrophysics and Space Science》1983,95(1):123-129
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. 相似文献
11.
12.
《Chinese Astronomy and Astrophysics》1986,10(3):173-180
A statistical analysis of the absorption line density N(zabs) in the Lαforest of 16 high-redshift quasars shows that the line density is clearly dependent on the emission redshift of the quasar, zem. Not only is the mean density of all the Lα absorption lines larger for larger zem, but more importantly, for each given absorption redshift interval, N(zabs) is also positively correlated with zem. A two-factor variance analysis, with ejection velocity as the second factor, shows that the line density in the Lα forest depends sensitively on zem but not on the ejection velocity. These results are difficult to interpret by either the intervening or the ejecting hypothesis and are unlikely to be due to the selection effects suggested by Carswell et al. [13]. 相似文献
13.
Debiprosad Duari 《Journal of Astrophysics and Astronomy》1997,18(4):441-447
There have been claims, from time to time that there are periodicities in the redshift distribution of quasistellar objects.
These claims are examined from various statistical angles for the 2164 QSO redshifts available in the latest compilation by
Hewitt& Burbidge (1990). The statistical tests reveal moderate to strong evidence for periodicities ξ = 0.0565 and 0.01270-0.129. 相似文献
14.
The distributionsf(z) of the redshifts for active galaxies (Seyfert galaxies, radio galaxies, and quasars) have been studied. Some statistically-significant maxima and minima are observed in the distributionsf(z) for these objects. The significance of peaks and gaps increases for the brighter objects, for which the samples are more complete. The clustering of the Seyfert galaxies is significantly different from that of the nearby normal galaxies. The distributionf(z) for the radio galaxies is similar to the analogous distribution for the galaxy clusters. Three of the five peaks in the distributionf(z) for the radio quasars may be caused by the selection effects. Two peaks within the intervalsz (0.5, 0.7) and (1.0, 1.1) are probably real. The corresponding scales of the QSO clustering along the line-of-sight are about 100h
–1 Mpc (h is the Hubble constant in the units of 75 km s–1 Mpc–1). The possibility of some global quasi-periodical cycles for the processes of activity is discussed. The period of a cycle for the Seyfert and radio galaxies is about 1×108 years that corresponds to the distances of about 30h
–1 Mpc between the shells. 相似文献
15.
We applied power spectral analysis to the redshift distribution of the quasars associated with low-redshift galaxies. Periodicity is confirmed at a level of confidence >99%, with a period of Δln(1+z) = 0.206. This result is exactly the same as previously found for different quasar samples. The periodicity is not caused by any selection effect in the emission lines. The two phenomena, the periodicity in the redhsift distribution and the association of quasars with low-redhsift galaxies can both be rather well explained by a multiply-connected model of the universe. 相似文献
16.
《New Astronomy Reviews》2007,51(7):539-546
Cosmological gamma ray bursts (GRBs) are the brightest explosions in the Universe. Satellite detectors, such as Beppo-SAX, HETE2 and more recently Swift, have provided a wealth of data, including the localization and redshifts of subsets of GRBs. The redshift distribution has been utilized in several studies in attempts to constrain the evolving star formation rate and to probe GRB rate evolution in the high-redshift Universe. These studies find that the GRB luminosity function and/or the rate density evolve with redshift. We present a short review of the problems of constraining GRB rate evolution in the context of the complex mix of biases inherent in the redshift measurements. To disentangle GRB rate evolution from the biases prevalent in the redshift distribution will require accounting for the incompleteness of the observed redshift sample. We highlight the importance of formulating a ‘complete GRB selection function’ to account for the main sources of bias. 相似文献
17.
Can observational selection effects, tied with the existence of strong lines, explain the observed log (1 + z) periodicity of the quasar's histogram, as sometimes claimed? A first approach shows that one must distinguish radio from optical quasars. In the former case spectroscopic selection due to strong lines is investigated from the study of homogeneous samples. Then, the role played by pairs of strong lines in the redshift's determination is evaluated and it shows that teh spectroscopic selection cannot explain the observed periodicity of the radio quasar's histogram. The study of the complete sample confirms this conslusion. 相似文献
18.
With the Hewitt-Burbidge catalogue of quasars as our sample, separately for 3 sets of respectively 7, 11, and 13 spectral lines as the “key lines” in the identification of quasar redshifts, we derive the redshift distribution arising from the identification of the lines. A comparison between the calculated and observed distributions shows that 1) the two are clearly correlated, with a correlation coefficient of 0.56. 2) Similar peaks are present in both in the z-intervals 0.2 – 0.4, 0.8 – 0.9, 1.4 – 1.5, and particularly around 1.95, as well similar valleys at 0.1 and 1.5 – 1.8. 3) Both rise or fall together at z = 0.2, 0.3, 0.4, 0.8, 1.9, 1.4, 1.5, 1.6 and 1.7. It thus appears that selection effects play an important role in the redshift distribution of the quasars. 相似文献
19.
Sebastien C. Vauclair 《Astrophysics and Space Science》2004,290(1-2):205-213
As they are the largest virialized structures formed in the universe, galaxy clusters are good probes of evolution of dark matter haloes since their formation from the fluctuation of the CMB. While the local cluster abundance allows us to constrain the shape and amplitude of the mass distribution regarding to the matter density, their redshift distribution is much more sensitive to the matter density of the universe and allows us to break the degeneracy. Here I compare the modelized distribution of clusters with existing catalogs such as EMSS to derive constraints on ΩM, σ8 and γ. 相似文献