Angular Cross-correlation Function Research Articles

Toward the measurement of neutrino masses: Performance of cosmic magnification with submillimeter galaxies

Context. The phenomenon of magnification bias can induce a non-negligible angular correlation between two samples of galaxies with nonoverlapping redshift distributions. This signal is particularly clear when background submillimeter galaxies are used, and has been shown to constitute an independent cosmological probe. Aims. This work extends prior studies on the submillimeter galaxy magnification bias to the massive neutrino scenario, with the aim being to assess its sensitivity as a cosmological observable to the sum of neutrino masses. Methods. The measurements of the angular cross-correlation function between moderate redshift GAMA galaxies and high-redshift submillimeter H-ATLAS galaxies are fit to the weak lensing prediction down to the arcmin scale. The signal is interpreted under the halo model, which is modified to accommodate massive neutrinos. We discuss the impact of the choice of cosmological parametrization on the sensitivity to neutrino masses. Results. The currently available data on the magnification bias affecting submillimeter galaxies are sensitive to neutrino masses when a cosmological parametrization in terms of the primordial amplitude of the power spectrum (As) is chosen over the local root mean square of smoothed linear density perturbations (σ8). A clear upper limit on the sum of neutrino masses can be derived if the value of As is either fixed or assigned a narrow Gaussian prior, a behavior that is robust against changes to the chosen value.

Methodological refinement of the submillimeter galaxy magnification bias

Aims. The main goal of this work is to test the results of a methodological improvement in the measurement of the magnification bias signal on a sample of submillimeter galaxies. In particular, we investigate the constraining power of cosmological parameters within the ΛCDM model. We also discuss important points that can affect the results. Methods. We measured the angular cross-correlation function between a sample of foreground GAMA II galaxies in a single wide spectroscopic redshift bin of 0.2 < z < 0.8 and a sample of background submillimeter galaxies from Herschel-ATLAS. We focused on the photometric redshift range of 1.2 < z < 4.0, with an improved methodological framework. Interpreting the weak lensing signal within the halo model formalism and performing a Markov chain Monte Carlo (MCMC) algorithm, we obtained the posterior distribution of both the halo occupation distribution and cosmological parameters within a flat ΛCDM model. Our analysis was also performed with additional galaxy clustering information via a foreground angular auto-correlation function. Results. We observed an overall remarkable improvement in terms of uncertainties in both the halo occupation distribution and cosmological parameters with respect to previous results. A priori knowledge about β, the logarithmic slope of the background integral number counts, is found to be paramount to derive constraints on σ8 when using the cross-correlation data alone. Assuming a physically motivated prior distribution for β, we obtain mean values of Ωm = 0.23−0.06+0.03 and σ8 = 0.79−0.10+0.10 and an unconstrained distribution for the Hubble constant. These results are likely to suffer from sampling variance, since one of the fields, G15, appears to have an anomalous behavior with a systematically higher cross-correlation. We find that removing it from the sample yields mean values of Ωm = 0.27−0.04+0.02 and σ8 = 0.72−0.04+0.04 and, for the first time, a (loose) restriction of the Hubble constant is obtained via this observable: h = 0.79−0.14+0.13. The addition of the angular auto-correlation of the foreground sample in a joint analysis tightens the constraints, but also reveals a discrepancy between both observables that might be an aggravated consequence of sampling variance or due to the presence of unmodeled aspects on small and intermediate scales.

Angular X-ray Cross-Correlation Analysis (AXCCA): Basic Concepts and Recent Applications to Soft Matter and Nanomaterials

Angular X-ray cross-correlation analysis (AXCCA) is a technique which allows quantitative measurement of the angular anisotropy of X-ray diffraction patterns and provides insights into the orientational order in the system under investigation. This method is based on the evaluation of the angular cross-correlation function of the scattered intensity distribution on a two-dimensional (2D) detector and further averaging over many diffraction patterns for enhancement of the anisotropic signal. Over the last decade, AXCCA was successfully used to study the anisotropy in various soft matter systems, such as solutions of anisotropic particles, liquid crystals, colloidal crystals, superlattices composed by nanoparticles, etc. This review provides an introduction to the technique and gives a survey of the recent experimental work in which AXCCA in combination with micro- or nanofocused X-ray microscopy was used to study the orientational order in various soft matter systems.

THE QUASAR-LBG TWO-POINT ANGULAR CROSS-CORRELATION FUNCTION ATz∼ 4 IN THE COSMOS FIELD

In order to investigate the origin of quasars, we estimate the bias factor for low-luminosity quasars at high redshift for the first time. In this study, we use the two-point angular cross-correlation function (CCF) for both low-luminosity quasars at $-24<M_{\rm 1450}<-22$ and Lyman-break galaxies (LBGs). Our sample consists of both 25 low-luminosity quasars (16 objects are spectroscopically confirmed low-luminosity quasars) in the redshift range $3.1<z<4.5$ and 835 color-selected LBGs with $z^{\prime}_{\rm LBG}<25.0$ at $z\sim4$ in the COSMOS field. We have made our analysis for the following two quasar samples; (1) the spectroscopic sample (the 16 quasars confirmed by spectroscopy), and (2) the total sample (the 25 quasars including 9 quasars with photometric redshifts). The bias factor for low-luminosity quasars at $z\sim4$ is derived by utilizing the quasar-LBG CCF and the LBG auto-correlation function. We then obtain the $86\%$ upper limits of the bias factors for low-luminosity quasars, that are 5.63 and 10.50 for the total and the spectroscopic samples, respectively. These bias factors correspond to the typical dark matter halo masses, log $(M_{\rm DM}/(h^{-1}M_{\odot}))=$$12.7$ and $13.5$, respectively. This result is not inconsistent with the predicted bias for quasars which is estimated by the major merger models.

AzTEC/ASTE 1.1-mm survey of SSA22: Counterpart identification and photometric redshift survey of submillimetre galaxies

We present the results from a 1.1 mm imaging survey of the SSA22 field, known for having an overdensity of z=3.1 Lyman-alpha emitting galaxies (LAEs), taken with the AzTEC camera on the Atacama Submillimeter Telescope Experiment (ASTE). We imaged a 950 arcmin$^2$ field down to a 1 sigma sensitivity of 0.7-1.3 mJy/beam to find 125 submillimeter galaxies (SMGs) with a signal to noise ratio >= 3.5. Counterpart identification using radio and near/mid-infrared data was performed and one or more counterpart candidates were found for 59 SMGs. Photometric redshifts based on optical to near-infrared images were evaluated for 45 SMGs of these SMGs with Spitzer/IRAC data, and the median value is found to be z=2.4. By combining these estimation with estimates from the literature we determined that 10 SMGs might lie within the large-scale structure at z=3.1. The two-point angular cross-correlation function between LAEs and SMGs indicates that the positions of the SMGs are correlated with the z=3.1 protocluster. These results suggest that the SMGs were formed and evolved selectively in the high dense environment of the high redshift universe. This picture is consistent with the predictions of the standard model of hierarchical structure formation.

A statistical study of gaseous environment of Spitzer interstellar bubbles

The expansion of interstellar bubbles is suggested to be an important mechanism of triggering material accumulation and star formation. In this work, we investigate the gaseous environment of a large sample of interstellar bubbles identified by the Spitzer space telescope, aiming to explore the possible evidence of triggered gas accumulation and star formation in a statistical sense. By cross-matching 6124 Spitzer interstellar bubbles from the Milky Way Project (MWP) and more than 2500 Galactic H ii regions collected by us, we obtain the velocity information for 818 MWP bubbles. To study the gaseous environment of the interstellar bubbles and get rid of the projection effect as much as possible, we constrain the velocity difference between the bubbles and the 13CO(1−0) emission extracted from the Galactic Ring Survey (GRS). Three methods: the mean azimuthally averaged radial profile of 13CO emission, the surface number density of molecular clumps and the angular cross-correlation function of MWP bubbles and the GRS molecular clumps are adopted. Significant over density of molecular gas is found to be close to the bubble rims. 60 per cent of the studied bubbles were found to have associated molecular clumps. By comparing the clump-associated and the clump-unassociated MWP interstellar bubbles, we reveal that the bubbles in associations tend to be larger and thicker in physical sizes. From the different properties shown by the bubble-associated and bubble-unassociated clumps, we speculate that some of the bubble-associated clumps result from the expansion of bubbles. The fraction of the molecular clumps associated with the MWP bubbles is estimated to be about 20 per cent after considering the projection effect. For the bubble-clump complexes, we found that the bubbles in the complexes with associated massive young stellar object(s) (MYSO(s)) have larger physical sizes, hence the complexes tend to be older. We propose that an evolutionary sequence might exist between the relatively younger MYSO-unassociated bubble-clump complexes and the MYSO-associated complexes.

The statistics of triggered star formation: an overdensity of massive young stellar objects around Spitzer bubbles

We present a detailed statistical study of massive star formation in the environment of 322 Spitzer mid-infrared bubbles by using the RMS survey for massive Young Stellar Objects (YSOs). Using a combination of simple surface density plots and a more sophisticated angular cross-correlation function analysis we show that there is a statistically significant overdensity of RMS YSOs towards the bubbles. There is a clear peak in the surface density and angular cross-correlation function of YSOs projected against the rim of the bubbles. By investigating the autocorrelation function of the RMS YSOs we show that this is not due to intrinsic clustering of the RMS YSO sample. RMS YSOs and Spitzer bubbles are essentially uncorrelated with each other beyond a normalised angular distance of two bubble radii. The bubbles associated with RMS YSOs tend to be both smaller and thinner than those that are not associated with YSOs. We interpret this tendency to be due to an age effect, with YSOs being preferentially found around smaller and younger bubbles. We find no evidence to suggest that the YSOs associated with the bubbles are any more luminous than the rest of the RMS YSO population, which suggests that the triggering process does not produce a top heavy luminosity function or initial mass function. We suggest that it is likely that the YSOs were triggered by the expansion of the bubbles and estimate that the fraction of massive stars in the Milky Way formed by this process could be between 14 and 30%.

Momentum transfer resolved memory in a magnetic system with perpendicular anisotropy

We have used resonant, coherent soft x-ray scattering to measure wave vector resolved magnetic domain memory in Co/Pd multilayers. The technique uses angular cross correlation functions and can be applied to any system with circular annuli of constant values of scattering wave vector q. In our Co/Pd film, the memory exhibits a maximum at q=0.0384 nm−1 near initial reversal that decreases in magnitude as the magnetization is further reversed. The peak is attributed to bubble domains that nucleate reproducibly near initial reversal and which grow into a labyrinth domain structure that is not reproduced from one magnetization cycle to the next.

X-ray cross-correlation analysis and local symmetries of disordered systems: General theory

In a recent article (P.Wochner et al., PNAS (2009)) x-ray scattering intensity correlations around a ring, in the speckle diffraction pattern of a colloidal glass, were shown to display a remarkable ~ cos(n $\phi$) dependence on the angular coordinate $\phi$ around the ring, with integer index n depending on the magnitude of the scattering wavevector. With an analytical derivation that preserves full generality in the Fraunhofer diffraction limit, we clarify the relationship of this result to previous x-ray studies of bond-orientation order, and provide a sound basis to the statement that the angular intensity correlations deliver information on local bond arrangements in a disordered (or partially ordered) system. We present a detailed analysis of the angular cross-correlation function and show its applicability for studies of wide range of structural properties of disordered systems, from local structure to spatial correlations between distant structural elements.

Not enough evidence to support the correlation between gamma-ray bursts and foreground galaxy clusters in the Swift Era

The correlation between distant Gamma-Ray Bursts (GRBs) and foreground galaxy clusters is re-examined by using the well localized (with an accuracy down to a few arcsec) Swift/XRT GRBs. The galaxy clusters are compiled from both the X-ray selected ROSAT brightest cluster sample (BCS) and the BCS extension by requiring δ ≥ 0° and b ≥ 20°. The Swift/XRT GRBs fulfilling the above selection criteria are cross-correlated with the clusters. Both Nearest–Neighbor analysis and the angular two-point cross-correlation function show that there is not enough evidence supporting the correlation between the GRBs and foreground clusters. We suggest that the non-correlation is probably related to the GRB number-flux relation slope.

CARS: the CFHTLS-Archive-Research Survey

Context. We present the CFHTLS-Archive-Research Survey (CARS). It is a virtual multi-colour survey that is based on public archive images from the Deep and Wide components of the CFHT-Legacy-Survey (CFHTLS). Our main scientific interests in the CFHTLS Wide-part of CARS are optical searches for galaxy clusters from low to high redshift and their subsequent study with photometric and weak-gravitational lensing techniques.Aims. As a first step in the CARS project, we present multi-colour catalogues from 37 sq. degrees of the CFHTLS-Wide component. Our aims are first to create astrometrically and photometrically well-calibrated co-added images from publicly available CFHTLS data. Second, we offer five-band () multi-band catalogues with an emphasis on reliable estimates for object colours. These are subsequently used for photometric redshift estimates.Methods. We consider all those CFHTLS-Wide survey pointings that were publicly available on January 2008 and that also have five-band coverage in . The data were calibrated and processed with our GaBoDS/THELI image processing pipeline. The quality of the resulting images was thoroughly checked against the Sloan-Digital-Sky Survey (SDSS) and already public high-end CFHTLS data products. From the co-added images we extracted source catalogues and determined photometric redshifts using the public code Bayesian Photometric Redshifts (BPZ). Fifteen of our survey fields directly overlap with public spectra from the VIMOS VLT deep (VVDS), DEEP2 and SDSS redshift surveys, which we used for calibration and verification of our redshift estimates. Furthermore we applied a novel technique, based on studies of the angular galaxy cross-correlation function, to quantify the reliability of photo-z 's.Results. With this paper we present 37 sq. degrees of homogeneous and high-quality five-colour photometric data from the CFHTLS-Wide survey. The median seeing of our data is better than in all bands and our catalogues reach a limiting magnitude of about 24.5. Comparisons with the SDSS indicate that most of our survey fields are photometrically calibrated to an accuracy of 0.04 mag or better. This allows us to derive photometric redshifts of homogeneous quality over the whole survey area. The accuracy of our high-confidence photo-z sample (10-15 galaxies per sq. arcmin) is estimated with external spectroscopic data to 0.04-0.05 up to < 24 with typically only 1-3% outliers. In the spirit of the Legacy Survey we make our catalogues available to the astronomical community. Our products consist of multi-colour catalogues and supplementary information, such as image masks and JPEG files to visually inspect our catalogues. Interested users can obtain the data by request to the authors.

On the correlation of short gamma-ray bursts and clusters of galaxies

Abstract We cross-correlate gamma-ray bursts (GRBs) and X-ray selected clusters of galaxies at z≤ 0.45. We find a positive 2σ signal for the angular cross-correlation function wbc(θ) on scales θ≤ 3° between short GRBs and clusters. Conversely, no correlation is found between clusters and the population of long GRBs. The comparison with the cluster autocorrelation function shows that short GRBs do not trace the cluster distribution, as not all short GRBs are found in clusters. A higher signal in wbc(θ) is found if we only consider the cluster population up to z= 0.1. By comparing the short-burst autocorrelation function with model predictions, we then constrain short bursts to mostly originate within ∼270 Mpc (i.e. z≤ 0.06). Our analysis also reveals that short GRBs are better correlated with ‘normal’ galaxies. The double compact-object merger model for short GRBs would associate them preferentially with early-type galaxies, but the present statistics do not allow us to exclude that at least a fraction of these events might also take place in late-type galaxies, in agreement with recent evidence.

Measurement of the gravitational potential evolution from the cross-correlation betweenWMAPand the APM Galaxy Survey

Models with late time cosmic acceleration, such as the Lambda-dominated CDM model, predict a freeze out for the growth of linear gravitational potential at moderate redshift z<1, what can be observed as temperature anisotropies in the CMB: the so called integrated Sachs-Wolfe (ISW) effect. We present a direct measurement of the ISW effect based on the angular cross-correlation function, w_{TG}, of CMB temperature anisotropies and dark-matter fluctuations traced by galaxies. We cross-correlate the first-year WMAP data in combination with the APM Galaxy survey. On the largest scales, theta = 4-10 deg, we detect a non-vanishing cross-correlation at 98.8 % significance level, with a 1-sigma error of w_{TG} = 0.35 +/- 0.14 microK, which favors large values of Omega_Lambda \simeq 0.8 for flat FRW models. On smaller scales, theta < 1deg, the correlations disappear. This is contrary to what would be expected from the ISW effect, but the absence of correlations may be simply explained if the ISW signal was being cancelled by anti-correlations arising from the thermal Sunyaev-Zeldovich (SZ) effect.

Red galaxy overdensities and the varied cluster environments of powerful radio sources with z 1.6

The environments of a complete subsample of six of the most powerful radio-loud active galactic nuclei (AGN) at redshifts z ∼ 1.6 are investigated, using deep RJK imaging to depths of R ∼ 26, J ∼ 22.4 and K ∼ 20.6. An excess of galaxy counts in the K band is seen across these fields; these surplus galaxy counts are predominantly associated with red galaxies (R − K 4) of magnitudes 17.5 K 20.5 found within radial distances of ∼1 Mpc of the AGN host. These are exactly (though not uniquely) the magnitudes, colours and locations that would be expected of old passive elliptical galaxies in cluster environments at the redshifts of these AGN. Using both an Abell-style classification scheme and investigations of the angular and spatial cross-correlation functions of the galaxies, the average environment of the fields around these AGN is found to be consistent with Abell cluster richness classes 0 and 1. The amplitude of the angular cross-correlation function around the AGN is shown to be a strong function of galaxy colour and is highest when only those galaxies with the colours expected of old elliptical galaxies at these redshifts are considered. The images cover a relatively wide field, 5 × 5 arcmin 2 , allowing the distribution of the surplus galaxy counts to be investigated. The galaxy overdensities are found on two scales around the AGN: (i) pronounced central concentrations on radial scales within ∼150 kpc; where present, these are composed almost entirely of red (R − K 4) galaxies, suggesting that the morphology‐density relation is imprinted into the centres of clusters at a high redshift; (ii) weaker large-scale excesses extending out to between 1 and 1.5-Mpc radius. The presence or absence of galaxy excesses on these two scales, however, differs greatly between the six different fields: the fields of two AGN do show red galaxy excesses on both scales, another two fields show only a large-scale red galaxy overdensity with no pronounced central concentration, and one field shows only a sharp central peak of red galaxies with no large-scale overdensity. The final field shows little evidence for an excess on any scale; this field is associated with an unresolved radio source, perhaps indicating that only extended radio sources probe cluster environments.

Molecular Dynamics Simulation Study of the Rotational and Translational Motions of Liquid Acetonitrile

By using molecular dynamics simulation, temperature and density dependences of the power spectra of the velocity autocorrelation functions of acetonitrile have been investigated. Strong temperature dependence was observed only in the low frequencies of ≤30 cm-1, where the contribution of the diffusive motion was predominant, while the density effect was observed in the whole spectral region of the low-frequency phonon modes. Not only the velocity autocorrelation functions but also the velocity and the angular velocity cross correlation functions were calculated to elucidate the liquid dynamics. The amount of the angular velocity cross correlation was smaller than that of the velocity cross correlation. Oscillations were observed for angular velocity cross correlation functions, which clearly indicate that a nonnegligible portion of the initial angular momentum of the central molecule transferred to the surrounding molecules was given back to the central molecule for some time before the eventual spread over the system. We found that the angular velocity cross correlation function between the central molecule and the molecules in the outer half of the first coordination shell is negative in the short times, which suggests that the molecules move like a pair of coupled gears. Such molecular motion may be important for the diffusion process in the liquid.

The local environment of H II galaxies

We have carried out an investigation of the environments of low redshift HII galaxies by cross-correlating their positions on the sky with those of faint field galaxies in the Automatic Plate Measuring Machine catalogues. We address the question of whether violent star formation in HII galaxies is induced by low mass companions by statistically estimating the mean space density of galaxies around them. We argue that even if low mass companions were mainly intergalactic HI clouds, their optical counterparts should be detectable at faint limits of the APM scans. A significantly positive signal is detected for the HII galaxy-APM galaxy angular cross-correlation function, but the amplitude is poorly determined. The projected cross-correlation function has higher signal-to-noise, and suggests that the amplitude is slightly lower than for normal field galaxies. This implies that these bursting dwarf galaxies inhabit slightly lower density environments to those of normal faint field galaxies, consistent with other studies of emission line galaxies. This suggests that in these dwarf starburst galaxies, star formation is not triggered by unusually strong tidal interactions, and must have a different origin.

Detection of a small defect on a rough surface

We report experimental results that show that the far-field correlation function is sensitive to a small local change in rough-surface geometry, where the speckle spatial correlation rather than the sample ensemble average is adopted. The angular cross-correlation function of the far-field speckles scattered by one-dimensional random rough surfaces is measured when a polarized beam of light is incident upon the rough surface from vacuum, where one part of the surface used is a thin dielectric film deposited upon a glass substrate and the other part is identical to the first except for a localized defect. We envisage application of this sensitivity property to inspection of a sample with a defect by means of speckle mapping.

Another X‐Ray–discovered Poor Cluster of Galaxies Associated with CL 0016+16

We report optical spectroscopic observations of RX J0018.8+1602, a ROSAT X-ray source proposed to be an intermediate-redshift cluster of galaxies. Our observations confirm the identification of RX J0018.8+1602 and provide measurements of its mean radial velocity (z = 0.5406 ± 0.0006) and velocity dispersion (σp=200−80+110 km s-1). This is the second poor cluster that has been found to be a companion to CL 0016+16 (z = 0.5455), the other one being RX J0018.3+1618 (z = 0.5506). The 0.2-2 keV band source-frame X-ray luminosity summed over both companion clusters is 5 × 1044 ergs s-1, which is a significant fraction (~23%) of the X-ray luminosity of the main cluster. The companions are located at angular distances of 10'-25' (minimum physical scales of 5-12 Mpc) from CL 0016+16, and we propose that they represent a new large-scale component of the X-ray emission from clusters of galaxies. Similar low X-ray luminosity poor clusters surrounding nearby Abell clusters can explain the excess power observed in the angular cross-correlation function between Abell clusters and the X-ray background on inferred physical scales of 14-20 Mpc.

QSO-galaxy correlations induced by weak lensing in arbitrary Friedmann-Lemaitre cosmologies

We calculate the angular cross-correlation function between background QSOs and foreground galaxies induced by the weak lensing effect of large-scale structures. Results are given for arbitrary Friedmann-Lemaitre cosmologies. The non-linear growth of density perturbations is included. Compared to the linear growth, the non-linear growth increases the correlation amplitude by about an order of magnitude in an Einstein-de Sitter universe, and by even more for lower Omega_0. The dependence of the correlation amplitude on the cosmological parameters strongly depends on the normalization of the power spectrum. The QSO-galaxy cross-correlation function is most sensitive to density structures on scales in the range (1-10) Mpc/h, where the normalization of the power spectrum to the observed cluster abundance appears most appropriate. In that case, the correlation strength changes by less than a factor of <~ 2 when Omega_0 varies between 0.3 and 1, quite independent of the value of Omega_Lambda. For Omega_0 <~ 0.3, the correlation strength increases with decreasing Omega_0, and it scales approximately linearly with the Hubble constant h.

Faint blue galaxies as a probe of the X-ray background at high redshift

We present a formalism describing the physical content of cross-correlation functions between a diffuse background and a population of discrete sources. The formalism is used to interpret cross-correlation signals between the unresolved X-ray background and a galaxy population resolved to high redshift in another spectral band. Specifically, we apply it to the so-called faint blue galaxy population and constrain their X-ray emissivity and clustering properties. A model is presented which satisfies the recently measured constraints on all 3 correlation functions (galaxy/galaxy, background/background and galaxy/background). This model predicts that faint galaxies in the magnitude range B=18-23 (cvering redshifts $z \lsim 0.5$) make up $\sim 22 \%$ of the X-ray background in the 0.5-2 keV band. At the mean redshift of the galaxy sample, $\bar z=0.26$, the comoving volume emissivity is $\rho_X \sim 6-9 \times 10^{38}h$ ergs s$^{-1}$Mpc$^{-3}$ . When extrapolated to fainter magnitudes, the faint blue galaxy population can account for most of the residual background at soft energy. We show how the measurement of the angular and zero-lag cross-correlation functions between increasingly faint galaxies and the X-ray background can allow us to map the X-ray emissivity as a function of redshift.