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1.
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
2.
In order to investigate the nature of the redshifts of QSOs, Hubble diagrams have been plotted. First, [log (cz),m
v
] pairs have been plotted for a sample of 252 QSOs. This sample has been drawn from the recent catalogue (Burbidgeet al., 1977) of 633 QSOs after excluding those for which either the redshifts are uncertain or theV magnitudes are not known accurately. Before plotting,K-correction has been applied to theV magnitudes. A least-squares linear fit has been obtained for this plot and, as a result, we get a slope of 0.165±0.012 against 0.2 expected theoretically on the basis of the assumption that the QSOs are at cosmological distances implied by their redshifts. The discrepancy in the value of the slope has been attributed partly to the uncertainty in theK-correction and partly to the evolutionary effect. In order to eliminate the uncertainty due to theK-correction, [log (cz), logf(H)] pairs have been plotted for a sample of 52 QSOs and a least-squares linear fit has been obtained which has a slope of –0.497±0.076, in close agreement with the theoretically expected value of –0.5. This lends support to the hypothesis that the redshifts of the QSOs are cosmological in nature. Finally, the evolutionary effect has been examined, and we conclude that the QSOs do evolve in luminosity in course of time. 相似文献
3.
Images of the Hubble Ultra Deep Field are analyzed to obtain a catalog of galaxies for which the angular sizes, surface brightness, photometric redshifts, and absolute magnitudes are found. The catalog contains a total of about 4000 galaxies identified at a high signal-to-noise ratio, which allows the cosmological relations angular size—redshift and surface brightness-redshift to be analyzed. The parameters of the evolution of linear sizes and surface brightness of distant galaxies in the redshift interval 0.5–6.5 are estimated in terms of a grid of cosmological models with different density parameters (Ω V ; Ω m ). The distribution of photometric redshifts of galaxies is analyzed and possible superlarge inhomogeneities in the radial distribution of galaxies are found with scale lengths as large as 2000 Mpc. 相似文献
4.
To form the Hubble diagram for quasi-stellar objects (QSOs),we have made use of the recently published data on X-ray fluxes
of 159 QSOs observed from the Einstein Observatory. The scatter in the Hubble diagram and the lack of an obvious redshift-flux
density correlation for these QSOs have been attributed to the observational selection effect that the intrinsically less
luminous QSOs can be detected only in the nearby region of space. When the optical, radio and X-ray selection effects are
removed, keeping only the intrinsically brighter sources, we obtain a sample of 16 QSOs having a small dispersion in X-ray
luminosities (〈 logL
x〉) = 46.12 ± 0.28), a statistically significant linear correlation between (logf
x, logcz) pairs and a slopeA =-1.906 ± 0.061 of the linear regression oflog f
x on logcz. This slope is consistent, at a confidence level of 95 per cent or greater, with the slope of-2.0 expected theoretically
based on the assumption that the redshifts of QSOs are cosmological in nature. 相似文献
5.
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
6.
J. A. Lester 《Astrophysics and Space Science》1993,207(2):231-248
We present anon-general relativistic cosmological model with the following features. All cosmological objects appear to be receding from each other. There are two mathematically distinct types of objects. Type I objects have apparent magnitudes and apparent angular diameters comparable to those for standard FLRW models. Their redshifts are bounded; this bound is at least 3. Type II objects can have unlimited redshifts. They appear significantly smaller than Type I objects with the same redshift, and (for redshifts greater than 1) appear brighter (and more so for larger redshifts). The model is an extension of classical de Sitter spacetime in which the location of infinity is allowed to be relative. 相似文献
7.
Pure luminosity evolution models for galaxies provide an unacceptable fit to the redshifts and colors of faint galaxies. In
this paper we demonstrate, using HST morphological number counts derived both from the I
814-band of WFPC2 in the Medium Deep Survey (MDS) and the Hubble Deep Field (HDF) and from the H
1.6-band of NICMOS, and ground-based spectroscopic data of the Hawaii Deep Field and the Canada-France Redshift Survey, that
number evolution is necessary for galaxies, regardless of whether the cosmic geometry is flat, open, or Λ-dominated. Furthermore,
we show that the number evolution is small at redshifts of z<1, but large at z>1, and that this conclusion is valid for all the three cosmological models under consideration. If the universe is open or
Λ-dominated, the models, which are subject to the constraint of the conservation of the comoving mass density of galaxies,
naturally predict a population of star-forming galaxies with the redshift distribution peaking at z=2∼ 3, which seems to be consistent with the recent findings from Lyman-break photometric selection techniques. If the cosmological
model is flat, however, the conservation of the comoving mass density is invalid. Hence, in order to account for the steep
slope of B-band number counts at faint magnitudes in the flat universe, such a star-forming galaxy population has to be introduced ad
hoc into the modelling alongside the merger assumption.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
The question of the association of quasars with galaxies is re-examined using 785 quasars at |b| 30, δ − 02°30′ in the new Hewitt and Burbidge Catalog (1980) and all galaxies in the “Uppsala General Catalogue of Galaxies” (Nilson, 1973). The results of the two-point cross-correlation function are presented and they show that there are on the average 0.153 ± 0.011 more galaxies within 10'.0 of a QSO than would be expected if the QSOs were distributed randomly. We find the marginal significance of the tendency for correlation between QSOs and galaxies to increase with increasing redshifts z or apparent magnitudes V. The nearest neighbor test has also been taken to analyse the same data as well as get further evidence for the apparent association between QSOs and galaxies. 相似文献
9.
We have calculated mosaic correlation maps based on the ILCWMAP microwave background data and infrared and optical extragalactic object positions according to the 2MRS catalog and the SDSS survey respectively. Using the histograms of signal values in pixels and angular power spectra, we have investigated the statistical properties of these maps. Evolution power spectra of correlation maps, depending on z, were built. We show that there are certain correlation scales (2°–3°) at different redshifts (z = 1–2), which can match the size of the maximal heterogeneity cell (60–90 Mpc) during different cosmological epochs. 相似文献
10.
D. Basu 《Journal of Astrophysics and Astronomy》2001,22(4):263-282
Optical variability of extragalactic objects, viz., QSOs, BL Lacs and Seyfert galaxies has been monitored systematically over
an appreciable period of time and a large amount of data have accumulated. The present work reports results of investigations
involving statistical analysis of updated data on relationships between variability and various observed properties of the
objects, viz., redshift, color indices, radio spectral index and absorption lines. It is found that at high frequencies (rest
frame) radio spectral index does not change significantly with the degree of variability. However, the degree of variability
depends on redshifts. On the other hand, presence or absence of absorption lines is significantly associated with variability
for QSOs with larger redshifts (z > 1.0), while no such relationship exists for QSOs at smaller redshifts (z < 1.0) or other objects. Correlation between color indices and redshifts depends on the degree of variability and the sample
chosen for the color index. 相似文献
11.
In the last few years, galaxies at redshifts up to z ∼ 1 have become accessible for medium-resolved spectroscopy thanks to the new generation of 10 m-class telescopes. With kinematic
and photometric information on spiral galaxies in this regime, well-known scaling relations like the Tully-Fisher relation
(TFR) can be studied over half a Hubble time. By comparison to local samples, these studies facilitate simultaneous tests
of the hierarchical merging scenario and stellar population models. Using the Very Large Telescope, we obtained spatially
resolved rotation curves of 78 spiral galaxies in the FORS Deep Field (FDF), covering all Hubble types from Sa to Sm/Irr at
redshifts 0.1 < z < 1.0. We find evidence for a B-band luminosity increase of up to 2 mag for low-mass spirals, whereas the most massive galaxies are of the same luminosity
as their local counterparts. In effect, the TFR slope decreases significantly. This would explain the discrepant results of
previous observational studies. We also present the velocity-size relation and compare it to the predictions of numerical
simulations based on the hierarchical merging scenario.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
Roman Tomaschitz 《Astrophysics and Space Science》2010,325(2):259-275
The impact of a cosmic time evolution of the gravitational constant on SN Ia luminosity and AGN/QSO luminosity functions is studied. The gravitational constant scales linearly with the Hubble parameter, its present-day variation being \(\dot{G}_{0}/G_{0}\approx 1.9\times 10^{-4}\)?Gyr?1, compatible with current bounds from lunar laser ranging. Distance moduli of Type Ia supernovae are fitted with a cosmic expansion factor derived from temperature variations of planetary paleoclimates, and a luminosity dependence on look-back time proportional to the varying gravitational constant is inferred from the Hubble diagram. A fit is performed to the comoving space density of X-ray-selected active galactic nuclei (AGNs) and optically selected quasars (QSOs) extending to redshifts z≈6. The initial steep increase of the AGN space density is reproduced by a redshift evolution depending solely on the Hubble parameter as scaling variable. The AGN luminosity scales with the Hubble parameter, and the scaling exponents of the luminosity function, composed of two competing power laws with exponential cutoff, are obtained. Based on the AGN luminosity function, flux-limited X-ray source counts are investigated. The counting functions are derived and put to test by fitting cumulative number counts of soft X-ray point sources compiled from ROSAT, XMM-Newton, and Chandra surveys. 相似文献
13.
In this paper, we study the nonlinear electrodynamics in the framework of f(T) gravity for FRW universe along with dust matter, magnetic and torsion contributions. We evaluate the equation of state and deceleration parameters to explore the accelerated expansion of the universe. The validity of generalized second law of thermodynamics for Hubble and event horizons is also investigated in this scenario. For this purpose, we assume polelike and power-law forms of scale factor and construct f(T) models. The graphical behavior of the cosmological parameters versus smaller values of redshift z represent the accelerated expansion of the universe. It turns out that the generalized second law of thermodynamics holds for all values of z with Hubble and event horizons in polelike scale factor whereas for power-law form, it holds in a specific range of z for both horizons. 相似文献
14.
We have succeeded in establishing a cosmological model with a non-minimally coupled scalar field φ that can account not only for the spatial periodicity or the picket-fence structure exhibited by the galaxy N-z relation of the 2dF survey but also for the spatial power spectrum of the cosmic microwave background radiation (CMB) temperature anisotropy observed by the WMAP satellite. The Hubble diagram of our model also compares well with the observation of Type Ia supernovae. The scalar field of our model universe starts from an extremely small value at around the nucleosynthesis epoch, remains in that state for sufficiently long periods, allowing sufficient time for the CMB temperature anisotropy to form, and then starts to grow in magnitude at the redshift z of ～1, followed by a damping oscillation which is required to reproduce the observed picket-fence structure of the N-z relation. To realize such behavior of the scalar field, we have found it necessary to introduce a new form of potential V(φ)∝ φ 2exp?(?q φ 2), with q being a constant. Through this parameter q, we can control the epoch at which the scalar field starts growing. 相似文献
15.
We have identified 22 galaxies with photometric redshifts zph=5–7 in the northern and southern Hubble Space Telescope deep fields. An analysis of the images of these objects shows that they are asymmetric and very compact (～1 kpc) structures with high surface brightness and absolute magnitudes of MB≈?20m. The average spectral energy distribution for these galaxies agrees with the distributions for galaxies with active star formation. The star formation rate in galaxies with zph=5–7 was estimated from their luminosity at λ=1500 Å to be ~30 M⊙yr?1. The spatial density of these objects is close to the current spatial density of bright galaxies. All the above properties of the distant galaxies considered are very similar to those of the so-called Lyman break galaxies (LBGs) with z ～ 3–4. The similarity between the objects considered and LBGs suggests that at z ～6, we observe the progenitors of present-day galaxies that form duringmergers of protogalactic objects and that undergo intense starbursts. 相似文献
16.
Halton Arp 《Astrophysics and Space Science》1990,167(2):183-219
The most accurate data on galaxy types, corrected apparent magnitudes and redshifts as given in the Sandage-TammanRevised Shapley-Ames catalog are analyzed. It is shown that Sb galaxies of the same luminosity class as M31 and M81 define a narrow Hubble relation withH
0=65
–6
+15
km s–1 Mpc–1.In contrast, Sc galaxies deviate strongly towars higher redshift from a linear, log redshift—apparent magnitude relation. Not all this deviation can be selection effect due to increasing volume sampled at increasing redshift (Malmquist bias). Physical associations of groups of galaxies in theRSA Catalog are used to establish the existence of various amounts of excess (non-velocity) redshifts among Sc and allied types of galaxies.Independent distances fromHi line width — luminosity criterion (Tully-Fisher) are analyzed. It is shown that this criterion gives much smaller distances than redshifts do for galaxies which deviate above the Hubble line. Unless the Tully-Fisher relation gives too small distances for more luminous galaxies, this confirms the excess redshift to be intrinsic to the Galaxy. But it is next demonstrated, that for low redshift galaxies, there is no discrepancy between redshift and Tully-Fisher distance even though there is a wide range of absolute magnitudes.If Tully-Fisher distances are accepted, the onlly alternative to having a Hubble constant which increases strongly with distance is to have a component of the higher redshift Sc's contributed by a non-recessional redshift. Streaming motions would have to be large, increase with distance and be always in the receding sence. It is shown here that the Sc's which deviate most from the Hubble relation and have the largest discrepancies with Tully-Filsher distances lie predominantly in the sky toward very nearby groups of galaxies. If they were at these closer distances the discordant galaxies, mostly ScI's, would have dwarfish physical properties but not so unprecedented as the large sizes which result from redshift distances.Finally the interaction of specific high redshift ScI's with nearby galaxies is presented as an independent proof that ScI's are generally small, low luminosity galaxies. This result furnishes insight into the long standing puzzle of how apparently distant ScI's can interact with nearby galaxies such as in Stephan's Quintet, Seyfert's Sextet and NGC 4151/4156. 相似文献
17.
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
18.
Two quasars SDSS J010013.02+280225.8 and J030642.51+185315.8 with redshifts z = 6.30 and z = 5.363 were recently discovered. Their apparent magnitudes in the standard cosmological model give the luminosities of Lbol ～ 4.3 × 1014L⊙ and Lbol ～ 3.4 × 1014L⊙. In the framework of modern concepts it is accepted that the energy release of quasars is provided by the accretion onto black holes with masses of 1.24 ± 0.19 × 1010M⊙ and 1.07 ± 0.27 × 1010M⊙. As within the standard cosmological model the ages of these objects are about one billion years, this creates serious difficulties for the scenario of formation of such objects. Here we interpret the ultra-high luminosities of quasars as the effect of lensing of their radiation by the foreground globular clusters or dwarf galaxies. 相似文献
19.
Based on the catalog of Junkkarinen et al. (1991), we analyze the space-time distribution of absorption systems in quasar spectra at cosmological redshifts z=0–3.7. The z distribution of absorbing matter is shown to have a pattern of alternating maxima (peaks) and minima (dips). Within statistical uncertainty, the positions of such peaks and dips do not depend on the direction of observation. We have found a periodicity in the distribution of absorption systems in the functions ln(1+z) and (1+z)?1/2. We show that the derived sequence of maxima and minima in the space-time distribution of absorbing matter is not a manifestation of the spatial large-scale structure alone, but it is more likely temporal in nature. The most probable source of the putative structure could be an alternation (in the course of cosmological evolution) of pronounced and depressed epochs with a characteristic time interval of 520±160 Myr, depending on the cosmological model chosen. 相似文献
20.
We aim at understanding the statistical properties of luminous sub-millimeter (submm) galaxies (SMGs) in the context of cosmological structure formation. By utilizing a cosmological N-body simulation to calculate the distribution of dark halos in the Universe, we consider the dust enrichment in individual halos by Type II supernovae (SNe II). The SN II rate is estimated under a star formation activity which is assumed to occur on a dynamical timescale in the dark matter potential. Our simple framework successfully explains the luminosity function, the typical star formation rate, and the typical dust mass of an observational SMG sample at z～3. We also examine the clustering properties of SMGs, since a positive cross correlation between SMGs and Lyα emitters (LAEs) is indeed observed by a recent observation. In the simulation, we select SMGs by FIR dust luminosity >1012 L ⊙, while LAEs are chosen such that the age and the virial mass are consistent with the observed LAE properties. The SMGs and LAEs selected in this way show a spatial cross correlation whose strength is consistent with the observation. This confirms that the SMGs really trace the most clustered regions at z～3 and that their luminosities can be explained by the dust accumulation as a result of their star formation activities. We extend our prediction to higher redshifts, finding that a statistical sample of submm galaxies at z≥6 can be obtained by ALMA with a 100 arcmin2 survey. With the same survey, a few submm galaxies at z～10 may be detected. 相似文献