Cluster-cluster Correlation Research Articles

Structural Evolution of Metastable Protein Aggregates in the Presence of Trivalent Salt Studied by (V)SANS and SAXS.

We present a study of the structural evolution of protein aggregates formed in solutions of a globular protein, β-lactoglobulin (BLG), in the presence of YCl3. These aggregates are often observed before crystallization starts and they are metastable with respect to the crystalline phase. Here we focus on the characterization of the hierarchical structure of this intermediate phase and its temperature dependent structure evolution using a combination of (very) small angle neutron and X-ray scattering (VSANS, SANS, and SAXS). Results show that the hierarchical structure ranges from nanometer scale protein monomer, dimer and compact protein clusters to micrometer scale fractal protein aggregates. Upon cooling, the overall hierarchical structure is preserved, but the evolution of the internal structure within the aggregates is clearly visible: the monomer-monomer correlation peak reduces its intensity and disappears completely at lower temperatures, whereas the cluster-cluster correlation is enhanced. At a larger length scale, the fractal dimension of protein aggregates increases. The kinetics of the structure change during a temperature ramp was further investigated using time-resolved SAXS. The time dependent SAXS profiles show clear isosbestic points and the kinetics of the structural evolution can be well described using a two-state model. These dynamic properties of protein aggregates on a broad length scale may be essential for being the precursors of nucleation.

轻核α团簇结构理论和实验研究进展

The degree of freedom of α cluster exists widely in light α conjugate nuclei, which not only plays essential roles in the synthesis of elements and abandance of elements in nuclear astrophysics but also serves as the natural laboratory to test various new many-body theories and nuclear force due to the available high precision data. This article briefly summarizes the different theoretical approaches for alpha-cluster and compares the results of 12C Hoyle state with these approaches. All the theories support the structure of Hoyle state with a more extended size compared with ground state. However, a consensus has not be reached about how α clusters stay inside Hoyle state, where several candidate states are possible, such as a condensate state, a gas or crystalline arrangements of the α-particles. Further more, we also introduce the new experimental measurements of a decay and collective excitation of rotational band. In order to pin down the existence form of a in Hoyle state, a deeper knowledge of the collective excitation of cluster is needed. The essential progress can only be possible by high combination of new data with high precision and new many-body theory, where the roles of nucleon-nucleon correlation, cluster-cluster correlation and continuum are needed to be included reasonably.

Galaxy cluster searches based on photometric redshifts in the four CFHTLS Wide fields

We have developed a method for detecting clusters in large imaging surveys, based on the detection of structures in galaxy density maps made in slices of photometric redshifts. This method was first applied to the Canada France Hawaii Telescope Legacy Survey (CFHTLS) Deep 1 field by Mazure et al. (2007), then to all the Deep and Wide CFHTLS fields available in the T0004 data release by Adami et al. (2010). The validity of the cluster detection rate was estimated by applying the same procedure to galaxies from the Millennium simulation. Here we analyse with the same method the full CFHTLS Wide survey, based on the T0006 data release. In a total area of 154 deg2, we have detected 4061 candidate clusters at 3sigma or above (6802 at 2sigma and above), in the redshift range 0.1<=z<=1.15, with estimated mean masses between 1.3 10^14 and 12.6 10^14 M_solar. This catalogue of candidate clusters will be available online via VizieR. We compare our detections with those made in various CFHTLS analyses with other methods. By stacking a subsample of clusters, we show that this subsample has typical cluster characteristics (colour-magnitude relation, galaxy luminosity function). We also confirm that the cluster-cluster correlation function is comparable to that obtained for other cluster surveys and analyze large scale filamentary galaxy distributions. We have increased the number of known optical high redshift cluster candidates by a large factor, an important step towards obtaining reliable cluster counts to measure cosmological parameters. The clusters that we detect behave as expected for a sample of clusters fed by filaments at the intersection of which they are located.

Electrical and Magnetic Properties of Co/CoO Core-Shell Clusters

The need of increasing the density in magnetic recording media motivates the studies on magnetic clusters. In this context, we present a study of the magnetic transport properties in granular systems consisting in layers of cobalt-cobalt oxide core-shell clusters. The cluster diameter is 4 to 5 nm, with an approximately 1 nm oxide shell. The low temperature magnetoresistance and magnetization indicate the effect of exchange bias. The magnetoresistance behavior depends on the distribution of the clusters magnetic moments direction and on the electronic mean free path. The association of magnetoresistance and magnetization measurements reveals the local correlations between magnetic moments. The correlation length is calculated from the resistance versus reduced magnetization curve: in the absence of cluster-cluster correlation, one expects a parabolic shape. The deviation from this behavior corresponds to the correlations between the magnetic moments of the clusters at the length scale of the mean free path.

Combining cluster observables and stacked weak lensing to probe dark energy: Self-calibration of systematic uncertainties

We develop a new method of combining cluster observables (number counts and cluster-cluster correlation functions) and stacked weak lensing signals of background galaxy shapes, both of which are available in a wide-field optical imaging survey. Assuming that the clusters have secure redshift estimates, we show that the joint experiment enables a self-calibration of important systematic errors inherent in these measurements, including the source redshift uncertainty and the cluster mass-observable relation, by adopting a single population of background source galaxies for the lensing analysis. The single source galaxy population allows us to use the relative strengths of the stacked lensing signals at different cluster redshifts for calibrating the source redshift uncertainty, which in turn leads to accurate measurements of the mean cluster mass in each redshift and mass bin. In addition, our formulation of the stacked lensing signals in Fourier space simplifies the Fisher matrix calculations, as well as the marginalization over the cluster off-centering effect which is one of the most significant uncertainties in the stacked lensing analysis. We show that upcoming wide-field surveys covering more than a few thousand square degrees yield stringent constraints on cosmological parameters including dark energy parameters, without any priors on nuisance parameters that model systematic uncertainties. Specifically, the stacked lensing information improves the dark energy figure of merit by a factor of 4, compared to that from the cluster observables alone. The primordial non-Gaussianity parameter can also be constrained with a level of $\ensuremath{\sigma}({f}_{\mathrm{NL}})\ensuremath{\sim}10$. In this method, the mean source redshift is well calibrated to an accuracy of 0.1 in redshift, and the mean cluster mass in each bin to 5--10% accuracies, which demonstrates the success of the self-calibration of systematic uncertainties from the joint experiment.

Rhythmic Cluster Generation in Strongly Driven Colloidal Dispersions

We study the response of a nematic colloidal dispersion of rods to a driven probe particle which is dragged with high speed through the dispersion perpendicular to the nematic director. In front of the dragged particle, clusters of rods are generated which rhythmically grow and dissolve by rotational motion. We find evidence for a mesoscopic cluster-cluster correlation length, independent of the imposed drag speed. Our results are based on nonequilibrium Brownian dynamics computer simulations and in line with a dynamical scaling theory.

The KPNO/Deeprange Distant Cluster Survey. I. The Catalog and the Space Density of Intermediate‐Redshift Clusters

We have conducted an automated search for galaxy clusters within a contiguous 16 deg2 I-band survey in the north Galactic hemisphere. A matched filter detection algorithm identifies 444 cluster candidates in the range 0.2 z 1.2. The full catalog is presented along with the results from a follow-up spectroscopic survey. The estimated redshift distribution of the cluster candidates is consistent with a constant comoving density over the range 0.2 ≤ zest ≤ 0.8. A decline in the cluster space density by more than a factor of 3 over this redshift range is rejected at the greater than 99.9% confidence level. We find that the space density of Λcl ≥ 40 clusters in our survey lies in the range (1.6-1.8) × 10-5 h Mpc-3, ~1.5 times higher than the local distribution of comparably rich Abell richness class ≥0 clusters. The Λcl distribution is consistent with a power law. The discrepancy between the space density of Abell clusters and the clusters in this survey declines quickly as Λcl increases, suggesting that the difference at lower richness is due to significant incompleteness in the Abell catalog. A percolation analysis reveals that 10%-20% of the spectroscopically confirmed distant clusters are linked into superclusters at overdensities between 10 < δρ/ρ < 50, similar to what is seen in the local cluster distribution. This suggests that there has been little evolution of the cluster-cluster correlation length for z 0.5.

The Las Campanas Distant Cluster Survey Correlation Function

We present the first nonlocal (z > 0.2) measurement of the cluster-cluster spatial correlation length, using data from the Las Campanas Distant Cluster Survey (LCDCS). We measure the angular correlation function for velocity dispersion-limited subsamples of the catalog at estimated redshifts of 0.35 ≤ zest < 0.575 and derive spatial correlation lengths for these clusters via the cosmological Limber equation. The correlation lengths that we measure for clusters in the LCDCS are consistent both with local results for the APM cluster catalog and with theoretical expectations based upon the Virgo Consortium Hubble Volume simulations and the analytic predictions. Despite samples containing over 100 clusters, our ability to discriminate between cosmological models is limited because of statistical uncertainty.

The correlation function of radio sources

We investigate the large-scale clustering of radio sources in the Green Bank and Parkes-MIT-NRAO 4.85 GHz surveys by measuring the angular two-point correlation function w(\theta). Excluding contaminated areas, the two surveys together cover 70 per cent of the whole sky. We find both surveys to be reasonably complete above 50 mJy. On the basis of previous studies, the radio sources are galaxies and radio-loud quasars lying at redshifts up to z \sim 4, with a median redshift z \sim 1. This provides the opportunity to probe large-scale structures in a volume far larger than that within the reach of present optical and infrared surveys. We detect a clustering signal w(\theta) \approx 0.01 for \theta = 1\degr. By assuming an evolving power-law spatial correlation function in comoving coordinates \xi(r_c,z) = ( r_c / r_0 )^{-\gamma} (1+z)^{\gamma-(3+\epsilon)}, where \gamma = 1.8, and the redshift distribution N(z) of the radio galaxies, we constrain the r_0--\epsilon parameter space. For `stable clustering' (\epsilon = 0), we find the correlation length r_0 \approx 18 Mpc/h, larger than the value for nearby normal galaxies and comparable to the cluster-cluster correlation length.

Evolution of Clusters in Cold Plus Hot Dark Matter Models

We use N-body simulations to study evolution of galaxy clusters over the redshift interval 0 <= z <= 0.5 in cosmological models with a mixture of cold and hot dark matter (CHDM). Four different techniques are utilized: the cluster-cluster correlation function, axial ratios and quadrupoles of the dark matter distribution in individual clusters, and virial properties. We find that the correlation function for clusters of the same mass limit was larger and steeper at high redshifts. The slope increases from 1.8 at z=0 to 2.1 at z=0.5. Comoving correlation length r_c scales with the mass limit M within comoving radius 1.5 h^-1 Mpc and the redshift z as r_c ~= 20(1+z)(M/M_*)^1/3, where M_* = 3*10^14 h^-1 M_sun. When the correlation length is normalized to the mean cluster separation d_c, it remains almost constant: r_c~=(0.45-0.5) d_c. For small masses (M_clust <2*10^14 h^-1 M_sun) there is an indication that r_c goes slightly above the relation with the constant of proportionality being ~= 0.55-0.6. Anisotropy of density distribution in a cluster shows no change over redshift with axial ratios remaining constant around 1.2. In other words, clusters at present are as elongated as they were at the epoch of their first appearance. While the anisotropy of clusters does not change with time, the density profile shows visible evolution: the slope of density profile changes from gamma ~= -3.5 at z=0.5 to gamma ~= -2.5 at the present. We find that the core of a cluster remains essentially the same over time, but the density of the outlying regions increases noticeably. The virial relation M ~ v^2 is a good approximation, but there is a large fraction of clusters with peculiar velocities greater than given by this relation, and clusters with the same rms velocities have smaller masses in the past, a factor of 2 at z=0.5.

Large-scale structure formation for power spectra with broken scale invariance

We have simulated the formation of large-scale structure arising from COBE-normalized spectra computed by convolving a primordial double-inflation perturbation spectrum with the CDM transfer function. Due to the broken scale invariance ('BSI') characterizing the primordial perturbation spectrum, this model has less small-scale power than the (COBE-normalized) standard CDM model. The particle-mesh code (with $512^3$ cells and $256^3$ particles) includes a model for thermodynamic evolution of baryons in addition to the usual gravitational dynamics of dark matter. It provides an estimate of the local gas temperature. In particular, our galaxy-finding procedure seeks peaks in the distribution of gas that has cooled. It exploits the fact that ``cold" particles trace visible matter better than average and thus provides a natural biasing mechanism. The basic picture of large-scale structure formation in the BSI model is the familiar hierarchical clustering scenario. We obtain particle in cell statistics, the galaxy correlation function, the cluster abundance and the cluster-cluster correlation function and statistics for large and small scale velocity fields. We also report here on a semi-quantitative study of the distribution of gas in different temperature ranges. Based on confrontation with observations and comparison with standard CDM, we conclude that the BSI scenario could represent a promising modification of the CDM picture capable of describing many details of large-scale structure formation.

Galaxy Clustering in the Southern Hemisphere

AbstractIn this paper some of the major results from the COSMOS and APM digitised galaxy surveys are presented. The main motivation behind these catalogues was to study large-scale structure in the universe. We begin by outlining the importance of such studies to cosmology and discussing the early results from the visually compiled galaxy catalogues. The impact of the digitised catalogues is demonstrated by focussing on three key areas of research; the galaxy-galaxy two-point angular correlation function, the cluster-cluster spatial correlation function, and galaxy number counts.

Origin of cluster-cluster correlation functions in biased structure formation scenarios

view Abstract Citations (19) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Origin of Cluster-Cluster Correlation Functions in Biased Structure Formation Scenarios Watanabe, Takuya ; Matsubara, Takahiko ; Suto, Yasushi Abstract We have performed a series of N-body simulations in cold dark matter (CDM) cosmologies in order to study gravitational clustering properties of clusters of galaxies. Specifically, we consider two spatially flat CDM models: ({OMEGA}, λ, h, b) = (1.0. 0.0, 0.5, 1.7) and (0.2, 0.8, 0.75, 1.0), where {OMEGA}, λ, h, and b are the cosmological density parameter, the dimensionless cosmological constant, the Hubble parameter in units of 100 km s^-1^ Mpc^-1^, and the bias parameter, respectively. Clusters of galaxies in the simulations are identified applying an adaptive linking method. Their spatial clustering properties are compared with those for initial density peaks which would be possible sites for cluster formation. The latter predictions are independently obtained on the basis of random-Gaussian theory and from direct simulations. Almost all massive clusters identified in the simulations turn out to contain high-density peaks in qualitative agreement with the previously proposed idea of biased structure formation. Two-point correlation functions for clusters are approximately given by a power-law form and significantly exceed underlying mass correlations. The observed richness- dependent enhancement of the cluster correlation is well reproduced in low-density CDM models, while {OMEGA} = 1 models show weaker cluster correlation compared to the observational counterpart. Three-point correlation function and skewness of the clusters and peaks in these simulations are also discussed. Publication: The Astrophysical Journal Pub Date: September 1994 DOI: 10.1086/174544 Bibcode: 1994ApJ...432...17W Keywords: Astronomical Models; Computerized Simulation; Correlation; Cosmology; Dark Matter; Galactic Clusters; Galactic Evolution; Many Body Problem; Mathematical Models; Missing Mass (Astrophysics); Gravitational Fields; Hubble Constant; Mass Distribution; Spatial Distribution; Astrophysics; COSMOLOGY: THEORY; GALAXIES: CLUSTERING; GALAXIES: FORMATION; METHODS: NUMERICAL full text sources ADS |

Cluster-cluster correlation during irreversible diffusion-limited aggregation

In this paper, we discuss the evolution of the scattered intensityI(q) during irreversible diffusion-limited cluster-cluster aggregation. We analyse twodimensional simulations and interpret the results within the framework of a recently proposed theoretical approach. The theory describes the correlation among different clusters which develops during the irreversible aggregation process. The model is based on two coupled differential equations, controlling the growth of the average cluster mass and the time dependence of the probability of finding pairs of clusters as a function of their distance.

The zero-point of the cluster-cluster correlation function: A key test of cosmological power spectra

view Abstract Citations (37) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Zero-Point of the Cluster-Cluster Correlation Function: A Key Test of Cosmological Power Spectra Klypin, Anatoly ; Rhee, Geroge Abstract We propose the zero-point of the cluster-cluster correlation function r_0_ as a sensitive test for the shape of the power spectrum of initial fluctuations. With a wealth of new available redshifts for rich clusters the correlation function is measured to higher accuracy than has previously been done. It is now possible to go beyond the power law description to measure the point at which the correlation function becomes zero. A number of measurements of the zero-point of the rich galaxy cluster correlation function indicate that the zero-point should be in the range (40-60) h^-1^ Mpc. We discuss different effects, which could affect the zero-point and conclude that it is reasonably stable. The large value of r_0_ at which the zero-point occurs rules out conventional CDM models independently of the assumed amplitude. The most severe constraints are imposed on the CDM models with the cosmological constant. Models with {OMEGA} < 0.25 should he rejected because they predict too large r_0_. If the age of the universe is assumed to be larger than 15 Gyr, models with either {OMEGA} < 0.5 or h > 0.55 are rejected. We present the results of numerical simulations of clusters in the mixed model (the cold-plus-hot-dark-matter or CHDM). The correlation function of clusters in the model has a zero-point, r_0_ = 55 h^-1^ Mpc that matches the zero-point of the observed function and is very close to the zero-point predicted by the linear theory. The shape of the function on all available scales (up to 100 h^-1^ Mpc) is reproduced for both the Abell and the APM clusters. The CHDM model predicts the mass function for the clusters, which is higher than that given by Bahcall & Cen (1993) (masses are larger by a factor 1.5), but is compatible with the results of Biviano et al. (1993). Publication: The Astrophysical Journal Pub Date: June 1994 DOI: 10.1086/174252 arXiv: arXiv:astro-ph/9309034 Bibcode: 1994ApJ...428..399K Keywords: Cosmology; Dark Matter; Distribution Functions; Galactic Clusters; Power Spectra; Stellar Models; Variations; Computerized Simulation; Density (Number/Volume); Numerical Analysis; Red Shift; Stellar Mass; Astronomy; COSMOLOGY: THEORY; GALAXIES: CLUSTERING; COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE; METHODS: NUMERICAL; Astrophysics E-Print: 16 pages, tex, UNLV/93/32 full text sources arXiv | ADS |

A hydrodynamic approach to cosmology: The mixed dark matter cosmological scenario

We compute the evolution of spatially flat, mixed cold and hot dark matter (``MDM) models containing both baryonic matter and two kinds of dark matter. The mean final Zeldovich-Sunyaev $y$ parameter is estimated to be $\bar y=(5.4\pm 2.7)\times 10^{-7}$, with a rms fluctuation of approximately $\bar{\delta y}=(6.0\pm 3.0)\times 10^{-7}$ on arc minute scales. The rate of galaxy formation peaks at an even later epoch ($z\sim 0.3$) than in the standard ($\Omega=1$, $\sigma_8=0.67$) CDM model ($z\sim 0.5$) and, at a redshift of z=4 is nearly a factor of a hundred lower than for the CDM model with the same value of $\sigma_8$. The model yields a cluster mass function which is about a factor of 4 higher than observed but a cluster-cluster correlation length lower by a factor of 2 than what is observed but both are closer to observations than in the COBE normalized CDM model. The one dimensional pairwise velocity dispersion is $605\pm 8$km/s at $1h^{-1}$ separation, lower than that of the CDM model normalized to COBE, but still significantly higher than observations (Davis \& Peebles 1983). A plausible velocity bias $b_v=0.8\pm 0.1$ on this scale will reduce but not remove the discrepancy. Overall, the model is similar both on large and intermediate scales to the standard CDM model normalized to the same value of $\sigma_8$, but the problem with regard to late formation of galaxies is more severe in this model than in that CDM model. Adding hot dark matter significantly improves the ability of COBE normalized CDM scenario to fit existing observations, but the model is in fact not as good as the CDM model with the same $\sigma_8$ and is still probably unsatisfactory with regard to several critical tests.

The cluster-cluster correlation in hybrid models

view Abstract Citations (28) References (44) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Cluster-Cluster Correlation in Hybrid Models Jing, Y. P. ; Mo, H. J. ; Boerner, G. ; Fang, L. Z. Abstract Using N-body simulations, we have calculated the two-point correlation functions of the clusters of galaxies (ξ_cc_) in a set of hybrid (CDM + HDM + baryon) models. The galaxies are identified as density peaks above certain thresholds, to match the observed two-point correlation function of galaxies on scales <~10 h^-1^ Mpc. The clusters of galaxies are identified such that their number density is the same as that of Abell clusters. It is found that both the coherence length (the largest scale where ξ_cc_ remains positive) and the amplitude of ξ_cc_ increase systematically with the power of the initial density spectrum on large scales. For one model in which the power on large scales is sufficient to match the two-point angular correlation function of galaxies of the APM survey, ξ_cc_has a correlation length r_0_ = 23.0 +/- 0.9 h^-1^ Mpc and remains positive for r <~70 h^-1^ Mpc with a weak dependence on the richness of clusters, in good agreement with observations. Our results suggest that the observed large correlation length of Abell clusters, which is sometimes considered to be due to contaminations, should be expected in models which have enough power to explain the recent observations of galaxy clustering and motions on large scales. Publication: The Astrophysical Journal Pub Date: July 1993 DOI: 10.1086/172847 Bibcode: 1993ApJ...411..450J Keywords: Angular Correlation; Astronomical Models; Dark Matter; Galactic Clusters; Interacting Galaxies; Many Body Problem; Galactic Evolution; Galactic Structure; Universe; Astrophysics; COSMOLOGY: DARK MATTER; GALAXIES: CLUSTERING; COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE; METHODS: NUMERICAL full text sources ADS |

Clustering of galaxy clusters. I - Is the spatial cluster-cluster correlation function enhanced significantly by contaminations?

view Abstract Citations (33) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Clustering of Galaxy Clusters. I. Is the Spatial Cluster-Cluster Correlation Function Enhanced Significantly by Contaminations? Jing, Yi-Peng ; Plionis, Manolis ; Valdarnini, Riccardo Abstract We suggest that a consistency check of the redshift correlation function between three redshift samples of Abell clusters is able to distinguish whether the positive redshift correlations, found by Sutherland (hereafter Sutherland effect), at large redshift and small angular separations are mainly the result of foreground/background cluster contaminations or of real clustering. Our results do not support that contaminations are the origin of this effect. Instead, the observed features of the redshift correlation function are compatible with strong, richness-dependent clustering of small numbers of clusters which often results in supercluster elongations along the line of sight. To test this suggestion we have constructed a set of simulated cluster catalogs which have the same two-point correlation function and the same selection effects as the real samples. We found that the Sutherland effect is quite common in the simulated catalogs, which are completely free of contamination effects. The X^2^ test shows that the observed redshift correlation functions can be reproduced in the simulations more than 15%- 30% of the time, thus supporting that contaminations of the Abell cluster catalog are not necessarily the cause of this effect. Our results support that the rich cluster-cluster correlation function, as estimated by Bahcall & Soneira, is not significantly enhanced by such effects, and therefore the biased CDM model is still in disagreement with the observed clustering of clusters. Publication: The Astrophysical Journal Pub Date: April 1992 DOI: 10.1086/171226 Bibcode: 1992ApJ...389..499J Keywords: Cosmology; Dark Matter; Galactic Clusters; Red Shift; Astronomical Catalogs; Astronomical Models; Correlation; Digital Simulation; Power Spectra; Astrophysics; COSMOLOGY: OBSERVATIONS; GALAXIES: CLUSTERING; METHODS: NUMERICAL full text sources ADS | Related Materials (1) Part 2: 1992ApJ...398...12P

A SANS investigation on absolute scale of a homologous series of base-catalysed silica aerogels

Small angle neutron scattering data for a homologous series of base-catalysed silica aerogels are presented. The data are brought on an absolute scale by normalisation with water. Both oxidised and untreated samples are investigated, and it is found that oxidation does not alter the overall aerogel structure, the only effect of oxidation being the removal of surface groups. It is concluded that the samples are best described as consisting of elemental building blocks with a radial size of 20 Å, aggregated into clusters with a density dependent radius, 5–10 times larger than the building block size. The monolithic aerogel is formed by connection of these clusters. The existence of clusters in the aerogel structure is manifested in the data by the presence of cluster-cluster correlation effects. These effects are not observed in SANS spectra reported in the literature for neutrally reacted aerogels.

The correlation function of the 4-12 keV X-ray background intensity measured with the GINGA LAC

The angular autocorrelation function of the X-ray background in the energy band 4-12 keV has been explored on scales of 2°-25° using 132 exposures obtained with the Large Area Counter (LAC) on board the GINGA satellite. No significant signal is found over the whole range. An upper limit at 2° of 10 −4 is found for the autocorrelation function at the 95 per cent confidence level, significantly lower than previous values obtained in the 2-10 keV band at 3° separation. This upper limit is shown to constrain clustering on scales ∼ 10-300 Mpc in the high-redshift (z ∼ 0.1-5) Universe, and in particular the cluster-cluster and AGN-AGN correlation functions