Quasar Clustering Research Articles

Quasar Clustering and Spacetime Geometry

The non-Euclidean geometry of spacetime induces an anisotropy in the apparent correlation function of high-redshift objects, such as quasars, if redshifts and angles are converted to distances in naive Euclidean fashion. The degree of angular distortion depends on cosmological parameters, especially on the cosmological constant Λ, so this effect can constrain Λ independent of any assumptions about the evolution of luminosities, sizes, or clustering. We examine the prospects for distinguishing between low-density (Ω0 = 0.1-0.4) cosmological models with flat and open space geometry using the large quasar samples anticipated from the Two Degree Field Survey (2dF) and the Sloan Digital Sky Survey (SDSS). Along the way, we derive a number of results that are useful for studies of the quasar correlation function. In particular, we show that even these large quasar surveys are likely to reside in the sparse sampling regime for correlation function measurements, so that the statistical fluctuations in measurements are simply the Poisson fluctuations in the observed numbers of pairs. As a result, (1) one can devise a simple maximum likelihood scheme for estimating clustering parameters, (2) one can generate Monte Carlo realizations of correlation function measurements without specifying high-order correlation functions or creating artificial quasar distributions, and (3) for a fixed number of quasars, a deeper survey over a smaller area has greater statistical power than a shallow, large-area survey. If the quasar correlation length is equal to the value implied by recent (quite uncertain) estimates, then the 2dF and SDSS samples can provide clear discrimination between flat and open geometries for Ω0 ≤ 0.2 but only marginal discrimination for Ω0 = 0.4. Clear discrimination is possible for Ω0 = 0.4 if the true quasar correlation length is a factor of 2 larger, and a high-density survey of 30,000 quasars in 200 deg2 would provide clear discrimination even for the lower correlation length. Detection of quasar clustering anisotropy would confirm the cosmological spacetime curvature that is a fundamental prediction of general relativity.

The Locations of Gamma‐Ray Bursts Measured by COMPTEL

The COMPTEL instrument on the Compton Gamma Ray Observatory is used to measure the locations of gamma-ray bursts through direct imaging of MeV photons. In a comprehensive search, we have detected and localized 29 bursts observed between 1991 April 19 and 1995 May 31. The average location accuracy of these events is 125 (1 σ), including a systematic error of ~05, which is verified through comparison with Interplanetary Network (IPN) timing annuli. The combination of COMPTEL and IPN measurements results in locations for 26 of the bursts with an average "error box" area of only ~0.3 deg2 (1 σ). We find that the angular distribution of COMPTEL burst locations is consistent with large-scale isotropy and that there is no statistically significant evidence of small-angle autocorrelations. We conclude that there is no compelling evidence for burst repetition since no more than two of the events (or ~7% of the 29 bursts) could possibly have come from the same source. We also find that there is no significant correlation between the burst locations and either Abell clusters of galaxies or radio-quiet quasars. Agreement between individual COMPTEL locations and IPN annuli places a lower limit of ~100 AU (95% confidence) on the distance to the stronger bursts.

Quasar Clustering: Evidence for an Increase with Redshift and Implications for the Nature of Active Galactic Nuclei

The evolution of quasar clustering is investigated with a new sample of 388 quasars with 0.3 0.0 are excluded at a 0.3% probability level, compared with ~ 0.8 found for galaxies. The observed clustering properties appear qualitatively consistent with a scenario of Ω = 1 cold dark matter in which (1) the difference between the quasar and the galaxy clustering can be explained as a difference in the effective bias and redshift distributions and (2) the quasars, with a lifetime of t ~ 108 yr, sparsely sample halos of mass greater than Mmin ~ 1012-1013 h-1 M☉. We also discuss the possibility that the observed change in the quasar clustering is due to an increase in the fraction of early-type galaxies as quasar hosts at high z.

Quasar Radio Morphology and Clustering Environment at z~1/2

Quasar Radio Morphology and Clustering Environment at z~1/2

TYPICAL SCALES IN THE CLUSTERING OF THE UNIVERSE

The cosmic density perturbations are not completely scale-free, i.e. preferential scales should exist in the clustering of the universe. Observations do show the existence of the typical scales, namely, the distribution of various objects cannot be described by a simple fractal law. However, the standard two-point correlation function statistic is ineffective in detecting the typical scales. A better method based on identifying the periodic components in two-point correlation functions was developed. Using this method, the typical scales have been systematically searched for in samples of galaxies, clusters of galaxies, quasars and absorption lines of quasars. It showed the existence of typical scales in the range of 20–130 h−1 Mpc with high confidence. In particular, two typical scales, 60−1 Mpc and 130−1 Mpc, have been detected in all the samples being analysed. Such “universal” scales are probably the characteristic scales in the primordial fluctuations of the universe. Other theoretical implications of the detected typical scales have also been reviewed.

CLUSTERING AND LARGE-SCALE STRUCTURE WITH THE SLOAN DIGITAL SKY SURVEY

ABSTRACT The Sloan Digital Sky Survey (SDSS) will provide a complete imaging and spectroscopic survey of the high-latitude northern sky. The 2D survey will image the sky in five colors and will contain nearly 5 x 107 galaxies to g ~23m. The spectroscopic survey will obtain spectra of the brightest 106 galaxies, 105 quasars, and 1035 rich clusters of galaxies (to g ~18.3-19.3m, respectively). I summarize some of the science opportunities that will be made possible by this survey for studying the clustering and large-scale structure of the universe. The survey will identify a complete sample of several thousand rich clusters of galaxies, both in 2D and 3D--the largest automated sample yet available. The extensive cluster sample can be used to determine critical clustering properties such as the luminoisty-function, velocity-function, and mass-function of clusters of galaxies (a critical test for cosmological models), detailed cluster dynamics and Omegadyn, the cluster correlation function and its dependence on richness, cluster evolution, superclustering and voids to the largest scales yet observed, the motions of clusters and their large-scale peculiar velocity field, as well as detailed correlations between x-ray and optical properties of clusters, the density-morphology relation, and cluster-quasar associations. The large redshift survey, reaching to a depth of >~600h-1 Mpc, will accurately map the largest scales yet observed, determine the power-spectrum and correlation function on these large scales for different type galaxies, and study the clustering of quasars to high redshifts (z >~ 4). The implications of the survey for cosmological models, the dark matter, and Omega are also discussed.

The Analysis of Gravitational Lens Surveys. I. Selection Functions and Ambiguous Candidates

view Abstract Citations (28) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Analysis of Gravitational Lens Surveys. I. Selection Functions and Ambiguous Candidates Kochanek, Christopher S. Abstract Our analysis of the four optical surveys for gravitational lenses shows that only one more lens is expected among the unidentified image pairs found in the surveys. The best candidates and the estimated likelihood that they are lenses are 0011-012 at 36%, 2355-019 at 26%, DW 0400+258 at 18%, and 1318+111 at 10% and potentially 0205-379 at 69% because its companion is identified as a star only by its red color. The distributions of unidentified candidates from Crampton et al. (1992) and the ESO/Liège Survey in both separation from the quasar and magnitude are consistent with the expected distribution of Galactic stars. Stars are a important source of background contamination in lens surveys, and stellar companions to quasars become more common than lensed images at the confusion limit of approximately 2.5 (1.2) mag fainter than 17 (19) V mag quasars. Cross-comparisons of candidates in the four surveys show that point-spread function asymmetries are an unreliable means of identifying lens candidates for statistical purposes because they have a very high false positive rate. These candidates must be excluded from statistical analyses of lens surveys. We estimate the completeness of the surveys is near 80% for lenses produced by E and 50 galaxies and near 70% for spiral galaxies. We use the incidence of quasar-quasar pairs in the sample to estimate that the quasar-quasar correlation length is between 1 h-1(1 + Ζ)-1 Mpc ≲ r0 ≲ 18 h-1 (1 + Ζ)-1 Mpc, consistent with other measurements of quasar clustering. Publication: The Astrophysical Journal Pub Date: November 1993 DOI: 10.1086/173324 Bibcode: 1993ApJ...417..438K Keywords: COSMOLOGY: OBSERVATIONS; COSMOLOGY: GRAVITATIONAL LENSING; SURVEYS full text sources ADS | data products NED (59) SIMBAD (57) Related Materials (1) Part 2: 1993ApJ...419...12K

Quasar clustering on large scales

view Abstract Citations (43) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Quasar Clustering on Large Scales Mo, H. J. ; Fang, L. Z. Abstract The present results for quasar clustering on large scales are based on a sample of about 750 quasars, and are noted to be in good agreement with recent observations of galaxy clustering at low redshifts, suggest that the prediction that quasars trace the same large-scale structure as galaxies as clusters do is consistent with the observed quasar correlation. For an Einstein-de Sitter universe, the observed quasar correlation function would lead to a zero-redshift correlation amplitude comparable to that for Abell clusters; quasars may then represent high peaks in the initial density spectrum. Publication: The Astrophysical Journal Pub Date: June 1993 DOI: 10.1086/172766 Bibcode: 1993ApJ...410..493M Keywords: Galactic Clusters; Quasars; Universe; Astronomical Models; Correlation Coefficients; Density Distribution; Galactic Evolution; Power Spectra; Red Shift; Astrophysics; COSMOLOGY: OBSERVATIONS; GALAXIES: CLUSTERING; GALAXIES: QUASARS: GENERAL full text sources ADS |

Evidence for evolution in the clustering of quasars

We discuss the changes in the amplitude of the correlation function of quasar clustering with the redshift. Using the new Hewitt-Burbidge QSO catalogue, we find from a statistical analysis of the quasar pairs that the positive results of quasar clustering are mainly contributed by low-redshift quasars. There is an obvious change in the quasar distribution at z = 2. There is no clustering for z > 2. The difference in clustering is not due to any selection effect on the brightness. The evidence is that quasar clustering evolved with cosmological time.

Constraints on large-scale clustering from the autocorrelation properties of the X-ray background

Expectations for the angular correlation function of intensity fluctuations of the extragalacitc 2-10 keV X-ray background are discussed in relation to the two-point spatial correlation functions, xi(r), of X-ray sources. A simple analytic formula for the amplitude of intensity correlations, Gamma(theta), holding in the low-redshift, small-separation approximation, is derived. The HEAO 1 A-2 upper limits on Gamma(theta) have been exploited to derive constraints on the local xi(r) functions of rich clusters of galaxies, of AGNs, and on the AGN-cluster cross-correlation, as well as on evolution of the correlation functions with cosmic time. X-ray data are found to be compatible with the Bahcall and Soneira estimates of xi(cluster-cluster) as well as with the results of recent studies of quasar clustering.

QUASAR CLUSTERING AND ITS COSMOLOGICAL IMPLICATION

The clusterings of quasars and absorption line clouds have been analyzed from the viewpoint of the structure formation of the universe. It was found that the features of quasar clustering are quite different from those of galaxies. These results have already given several meaningful constraints on the structure formation, as follows: (a) quasar clustering is much weaker than in galaxies; (b) large scale structures, such as superclusters, should probably be formed after the epoch z~2; (c) the amplitude of the total density inhomogeneity seems to be less than that of galaxy distribution by at least a factor of 3–5 (in a Ω=1 universe); (d) Ly-α absorption clouds may be formed by different processes of clustering from that of glaxies.

Biased clustering in the cold dark matter cosmogony

We have used the Press–Schechter approximation to calculate the abundance and large-scale clustering of dark haloes in the CDM cosmogony. Applying these results to quasars at z = 3−4, we find a wide range of haloes which are both sufficiently massive and sufficiently numerous to host quasars, and the prediction for the clustering strength is correspondingly uncertain. Current estimates of quasar clustering require that the parent haloes lie at the most massive end of the allowed range, with velocity dispersions in the range 550−900 km s−1, and that the quasar luminosity be quite tightly correlated with the parent halo properties. Another application is to the diffuse X-ray background. If this is generated by discrete sources associated with dark haloes then the upper limits on the X-ray angular correlation function constrain the halo masses to be |$\lt 10^{12} \enspace h^{-1} \enspace M_\odot$|⁠. We have considered two simple models for galaxy formation. In the first, which has some attractions for disc galaxies, we identify galaxies with dark haloes forming at the present epoch. We find that haloes with abundance like that of |$L_\ast$| galaxies have large-scale clustering which is nearly unbiased, and the smaller haloes are antibiased — quite a negative feature. In the second, the galaxies we see today are assumed to be a fossil remnant of haloes which formed earlier. The stellar and dark particle velocity dispersions are assumed to be equal, and the luminosity for each halo is adjusted to give a tight and universal L–V relation like that observed. We identify an epoch when the comoving number density of haloes with a given luminosity is maximized, and we calculate how this number density is biased by long wavelength modes. The results here are more encouraging: All of the ‘galaxies’ in this model are positively biased. The enhancement of the light-to-mass ratios for rich clusters is substantial, though dependent on the normalization. For a low normalization the bias is strong enough to reconcile virial estimates of M/L for clusters with Ω = 1.

Clustering of quasars: An analysis of a sample of quasar candidates in SA 94

Two independent QSO surveys in Selected Area 94 have been completed and over 30 QSOs have been confirmed through slit spectra. From these data we estimated that the success rate of finding real QSO is about 80% and the surface density of QSOs for B<19.5 is about 5.4/sq deg. We studied the 2-dimensional clustering of quasars. Using the minimum interval statistics and the two point correlation function we found that the distribution of the observed sample on the sky did not differ significantly from a random distribution. However, there was a weak clustering for low redshift (z⩽2) quasars.

The Destruction of Quasars Clustering at z &gt; 2

The study of quasars clustering could become an important discriminant among different scenarios of the formation of large scale structure. The quasar clustering has now been confirmed and measured (Chu and Fang, 1986; Shaver, 1988) and the evolution of quasar clustering has been reported (Fang, Chu and Zhu, 1985; Chu and Fang, 1986). In the present work a large sample of about 3600 quasars in Hewitt-Burbidge catalog is employed and it is divided into several subsamples with different redshift ranges, a comparison of the correlation function in different subsamples provides then a mean of studying the evolution of the clustering with cosmology time.

Quasar clustering on large scales

La distribution a grande echelle (10-100 h− 1 Mpc) des quasars a redshifts eleves a ete mesuree en utilisant une nouvelle strategie des quasars. Deux tests statistiques d'agencement des quasars, la fonction de correlation et l'analyse en spectre de puissance sont discutes et compares. Ces tests sont appliques aux quasars pour les projections 2D et 3D des donnees. Les resultats sont compares a des simulations afin d'etablir une limite superieure a tout agencement actuel

The clustering of quasars

A combined sample of 376 quasars is used here to confirm previous reports of possible clustering of quasars at a high significance level. Evidence for the evolution of the clustering is also found. This evolution is relatively rapid, implying gravitational collapse on cluster scales. 18 references.

Quasar clustering in Sculptor and in the Veron catalog

Quasar clustering in Sculptor and in the Veron catalog

Quasar Clustering and the Evolution of Structure

Quasar clustering has now been confirmed at a high level of significance, and there is evidence for its evolution. A review is given of these developments, and of other evidence related to the evolution of structure.

Quasar Clustering at Intermediate Redshifts

This paper summarizes recent results from a study of quasar clustering based on a survey of U.K. Schmidt objective prism plates using the Automatic Plate Measuring facility at Cambridge. New procedures have been developed to detect quasars, eliminate contamination and measure accurate redshifts from the (see Drinkwater, M.J. 1987. Mon. Not. R. astr. soc., submitted). The redshift identifications are 90% reliable with an error (rms) of Δz = ±0.019 for quasars to a limiting magnitude of Bj = 19.5. Some 600 quasars from 6 U.K. Schmidt fields in the redshift range 1.8 &lt; z &lt; 2.6 have been analysed for weak clustering using power spectrum analysis (Webster, A. 1976. Mon. Not. R. astr. soc.175, 61). Plots of the statistic Q′ for 2-D and 3-D (4 fields only) projections of the data are given in the figure below. The ±1σ expectation values of Q′ calaulated for random simulations of the data (including non-uniform redshift selection and plate sensitivity) are indicated by vertical bars.

Evolution of Quasar Clustering

Using three deep samples of quasars, we have found strong evidence for quasar clustering and its evolution.