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1.
Peaks at high redshifts in individual samples of quasars can be explained as due to selection effects. It is concluded that peaks in quasar redshift distribution do not obey any generalformula that can constitute a periodicity, even though individual samples may favour some redshifts of smaller values, viz. z < 1.  相似文献   

2.
In former works (Zhouet al., 1983, 1985), a quantitative method have been developed to take the selection effects in the identification of emission lines of quasars into account. It was proved that these selection effects may be the cause of the unevenness in the redshift distribution of quasars. The present work is a continuation and development of former works. We use results given by the surveys with same limit-apparent magnitude and choose the quasars whose absolute magnitudes are within a specific range as the analysing samples. Using the method given in the former papers we may find out the evolutionary parameter in an evolutionary law with form of (1+z) y from the best fitting between the calculative and observational redshift distribution. The result of analysis shows that the evolutionary law of quasars selected by slitless technique isp =p 0(1 + z)6.5 ± 1 up toz=2.8. This result coincides with and generalizes the earlier result given by other authors.  相似文献   

3.
We made a power spectrum analysis on the quasar emission redshift distribution, and further confirmed the existence of periodicity in respect of the quantity x = F(z,qo) defined at (8).The existence of this periodicity does not mean that the quasar redshift is non-cosmological, for it can be interpreted as a remnant of density (acoustic) perturbations in the early big-bang universe. For this model, we made a number of tests. We found: 1) the ratio of periodic to non-periodic components falls as the sample size increases; 2) the periodicity should be more marked for quasars in one region of the sky than for all quasars, and 3) the Jeans wavelength before the recombination epoch determines the length of the period. Using this model we also found that qo > 0.5, lending further support to the conclusion reached by other means that the universe may be closed.  相似文献   

4.
The observed dependences of the spectral indices () of extragalactic radio sources on redshift (z) and radio luminosity (P) are investigated taking into account the possible luminosity selection effects in bright source samples. Using the steep spectrum (>0.5) extended (D>20 Kpc) sources from a compilation of three complete samples, the contribution of the luminosity selection effects to the observed -z relation is quantitatively estimated.We show that a highly significant fraction (54%) of the observed spectral steepening with redshift can be attributed to these luminosity selection effects present in most well-studied flux density-limited samples.  相似文献   

5.
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   

6.
Magnitude-redshift (m, z) relation within systems of galaxies is studied in detail in several kinds of systems. The main data contains 17 clusters, 64 groups, 121 pairs and 14 systems with two measured members, altogether 1043 galaxies in 162 separate systems. In addition, another sample of nearby groups and pairs, recently published data on six clusters with 121 measured members, as well as 65 compact galaxies in four groups and 23 pairs are studied. In Section 2 the data and the method are described. The numerical results for the main data are given in Table 1. There exists a significant positive (m, z)-relation in groups and pairs, but for clusters the same is valid only with a rather loose selection of members. The (m, z)-relations are calculated separately for each morphological type, but systematic differences between the types are not found. In Section 3 some properties of the velocity (redshift) dispersion σV are discussed. The joint dispersion decreases significantly from the early to the late types. This may point to an early dynamical state of the systems but it is also quite possible that this result is due to a selection effect. The presence of a selection effect in some commonly used samples of systems is indicated by the increase of velocity dispersion σV with increasing distance (Section 4). This effect which was first found for clusters and groups by SCOTT is present also in the larger sample of these systems and in the sample of pairs. Implications of this feature are discussed. As one of them, it is concluded in Section 5 that there exists no separate Canes Venatici cluster of galaxies but the galaxies supposed to form it belong to the Ursa Major cloud of galaxies. Several independent arguments supporting this conclusion are pointed out. In the Ursa Major-Canes Venatici complex of galaxies a distinct positive (m, z)-relation is found. In Section 4 the distance-dependence of the (m, z)-relations is studied and it is found that positive relations are most common for nearby systems. This is natural if the effect is an intergalactic one, the redshift being dependent on the distance of the galaxy. The (m, z)-relations is are studied as function of size of the systems in Section 6. It is found that σV, (m, z) regression coefficient bm, and parameter h which measures strength of redshift within the system, are largest in the systems with smallest radii. The result is opposite to that obtained using the virial theorem. In the Dopplerian context it would mean that the systems disperse the more rapidly the more dense these are. Dependence of the results on the number of data is studied in Section 7. As expected for a real effect, the frequency of positive relations increases with increasing number. The dispersion σV is usually larger in the central areas of the clusters than in the outskirts (Section 8). In these areas, σV is systematically larger for faint galaxies than for bright ones. The reason for large σV for faint galaxies projected on the centre is considered, studying in particular in the Coma cluster the velocity (redshift) distribution, colour-redshirt relation and morphological features which might be used in localization of the galaxies along the line of sight. The results of these three kinds of tests point to the possibility that redshift increases along the line of sight, but the results refer to sparse data and are very uncertain. A similar effect is suggested independently by observations of the galaxies in the background of the clusters. If true, the effect must be non-Dopplerian. In combination with brightness seggregation and preponderance of measured galaxies in the near side over those in the rear, this may cause the observed negative (m, z)-relations for some clusters. In SANDAGE 's and TAMMANN 's sample of nearby groups and pairs redshift appears dependent on luminosity class. This points to intrinsic redshifts in faint galaxies (Section 9). A similar implication is valid for the positive (m, z)-relations in the case of pairs and groups of compact galaxies (Section 10). Since there are indications of physical association in the latter case, the result cannot be explained by optical members. The present results are compared with previous ones in Section 11. This includes a study of redshifts with regard to brightness and surface brightness simultaneously, leading to a new statistical definition of relative compacity of galaxies belonging to the systems. Recent observations not included in the main data are viewed in Section 12. These show a positive (m, z)-relation. Interpretation of the results is discussed in Sections 13 and 14. From the numerous ones, three main possibilities remain, i. e. projected galaxies, intrinsic redshifts in faint galaxies and non-Dopplerian integalactic redshifts. There are several arguments suggesting that chance projections are not the principal explanation of the positive (m, z)-relations. If so, intrinsic redshifts in faint galaxies give probably the main explanation for pairs and small groups and integralactic redshifts for larger systems. This is in accordance with the general view of the redshift phenomenon in other scales. However, definitive proof of this conclusion could not be obtained from the present data which, though considerably large in number, is too small regarding the complexity of the problem.  相似文献   

7.
Discrete Fourier analysis on the quasar number count, as a function of redshift, z, calculated from the Sloan Digital Sky Survey DR6 release appears to indicate that quasars have preferred periodic redshifts with redshift intervals of 0.258, 0.312, 0.44, 0.63, and 1.1. However the same periods are found in the mean of the zConf parameter used to flag the reliability of the spectroscopic measurements. It follows that these redshift periods must result from some selection effect, as yet undetermined. It does not signal any intrinsic (quantized) redshifts in the quasars in Sloan survey data. However this result does not rule out the possibility as found in earlier studies of other data.  相似文献   

8.
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   

9.
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   

10.
High signal to noise neutral hydrogen observations of a complete sample of 132 galaxy pairs show a velocity difference distribution which decreases monotonically from zero. There is no strong indication of redshift periodicity for the entire sample and no indication at all for a subset of 79isolated galaxy pairs. In addition, when redshifts are corrected for the solar motion around the Galactic Center there is no indication of a redshift periodicity of 37.6 km s–1 in V for galaxy pairs (as suggested by Guthrie and Napier 1996).  相似文献   

11.
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   

12.
A study of the evolution of 377 rich ACO clusters with redshift z < 0.2 is presented. The data concerning galaxies in the investigated clusters were obtained using FOCAS packages applied to Digital Sky Survey I. The 377 galaxy clusters constitute a statistically uniform sample to which visual galaxy/star reclassifications were applied. Cluster shape within 2.0 h–1 Mpc from the adopted cluster centre (the mean and the median of all galaxy coordinates, the position of the brightest and of the third brightest galaxy in the cluster) was determined through its ellipticity calculated using two methods: the covariance ellipse method (hereafter CEM) and the method based on Minkowski functionals (hereafter MFM). We investigated ellipticity dependence on the radius of circular annuli, in which ellipticity was calculated. This was realized by varying the radius from 0.5 to 2 Mpc in steps of 0.25 Mpc. By performing Monte Carlo simulations, we generated clusters to which the two ellipticity methods were applied. We found that the covariance ellipse method works better than the method based on Minkowski functionals. We also found that ellipticity distributions are different for different methods used. Using the ellipticity‐redshift relation, we investigated the possibility of cluster evolution in the low‐redshift Universe. The correlation of cluster ellipticities with redshifts is undoubtly an indicator of structural evolution. Using the t‐Student statistics, we found a statistically significant correlation between ellipticity and redshift at the significance level of α = 0.95. In one of the two shape determination methods we found that ellipticity grew with redshift, while the other method gave opposite results. Monte Carlo simulations showed that only ellipticities calculated at the distance of 1.5 Mpc from cluster centre in the Minkowski functional method are robust enough to be taken into account, but for that radius we did not find any relation between e and z. Since CEM pointed towards the existence of the e (z) relation, we conclude that such an effect is real though rather weak. A detailed study of the e (z) relation showed that the observed relation is nonlinear, and the number of elongated structures grows rapidly for z > 0.14 (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

13.

We have produced a sample of 58 edge-on spiral galaxies at redshifts z ~ 1 selected in the Hubble Ultra Deep Field. For all galaxies we have analyzed the 2D brightness distributions in the V606 and i775 filters and measured the radial (hr) and vertical (hz) exponential scale lengths of the brightness distribution. We have obtained evidence that the relative thickness of the disks of distant galaxies, i.e., the ratio of the vertical and radial scale lengths, on average, exceeds the relative thickness of the disks of nearby spiral galaxies. The vertical scale length hz of the stellar disks of galaxies shows no big changes at z = 1. The possibility of the evolution of the radial scale length hz for the brightness distribution with redshift is discussed.

  相似文献   

14.
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   

15.
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.  相似文献   

16.
We present results of an investigation of clustering evolution of field galaxies between a redshift of z ∼ 1 and the present epoch. The current analysis relies on a sample of ∼ 14000 galaxies in two fields of the COMBO 17 survey. The redshift distribution extends to z ∼ 1. The amplitude of the three-dimensional correlation function can be estimated by means of the projected correlation function w(r p ). The validity of the deprojection was tested on the Las Campanas Redshift Survey (LCRS). In a flat cosmology with non-zero cosmological constant for bright galaxies (M B ≤-18) the clustering growth is proportional to (1+z) -2. However, the measured clustering evolution clearly depends on Hubble type. While locally the clustering strength of early type galaxies is equal to that of the bright galaxies, at high redshifts they are much stronger clustered, and thus the clustering has to evolve much more slowly. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

17.
The birefringence of electromagnetic radiation from gamma-ray burst (GRB) afterglows due to the Lorentz violation (LV) of spacetime has been calculated. The dependence of this effect on the radiation wavelength and redshift z in the ΛCDM model of the Universe has been established. It is shown that polarization tests for GRB afterglows can be invoked to measure the LV parameters. LV causes oscillations in the parameters of the afterglow spectrum that can be in the ultraviolet spectral range and will depend significantly on redshift z. This can facilitate the recording of LV for an electromagnetic field and can lower significantly the energy threshold of its detection.  相似文献   

18.
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.  相似文献   

19.
In this study, I attempt to apply for a new statistical method and investigate the environmental dependence of stellar mass and stellar velocity dispersion in the CMASS sample of the Sloan Digital Sky Survey Data Release 9 (SDSS DR9). I divide the CMASS sample with redshifts 0.44 ≤ z ≤ 0.59 into many subsamples with a redshift binning size of Δz = 0.01, and analyze the environmental dependence of stellar mass and stellar velocity dispersion of subsamples in each redshift bin. It is found that stellar mass and stellar velocity dispersions of CMASS galaxies are very weakly correlated with the local environment. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

20.
The Lehto-Tifft redshift quantization model is used to predict the redshift distribution for certain classes of quasars, and for galaxies in the neighborhood of z = 0.5. In the Lehto-Tifft model the redshift is presumed to arise from time dependent decay from an origin at the Planck scale; the decay process is a form of period doubling. Looking back in time reveals earlier stages of the process where redshifts should correspond to predictable fractions of the speed of light. Quasar redshift peaks are shown to correspond to the earliest simple fractions of c as predicted by the model. The sharp peaks present in deep field galaxy redshifts surveys are then shown to correspond to later stages in such a decay process. Highly discordant redshift associations are expected to occur and shown to be present in the deep field surveys. Peaks in redshift distributions appear to represent the spectrum of possible states at various stage of the decay process rather than physical structures. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

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