arXiv subjects

L. Van Waerbeke

Publications and source records attributed to L. Van Waerbeke.

41 records · Page 3Linked to original sources

arXiv1998

Measuring galaxy biasing with gravitational weak lensing

Gravitational weak lensing by large scale structures is view as a tool to probe the bias relation between the mass and the light distributions. It is explained how a particular statistic can be used to deproject the 2D mass distribution observed by weak lensing, in order to probe the bias at a given redshift and a given scale. Dependence with the cosmology is written, and observational issues are pointed out, like the importance of the redshift distribution of the galaxies. A signal to noise analysis shows that the scale dependence of the bias can be measured with a rather modest lensing survey size.

astro-ph↗

arXiv1996

Weak Lensing as a Probe of Dark Matter

Weak gravitational lensing of distant galaxies can probe the total projected mass distribution of foreground gravitational structures on all scales and has been used successfully to map the projected mass distribution of rich intermediate redshift clusters. This paper reviews the general concepts of the lensing analysis. We focus on the relation between the observable (shapes and fluxes) and physical (mass, redshift) quantities and discuss some observational issues and recent developments on data analysis which appear promising for a better measurement of the lensing signatures (distortion and magnification) at very large scales.

astro-ph↗

arXiv1996

The Auto-Correlation Function of the extragalactic background light: I. Measuring gravitational shear

A new method for measuring the shear induced by gravitational light deflection is proposed. It is based on analyzing the anisotropy induced in the auto-correlation function (ACF) of the extragalactic background light which is produced by very faint distant galaxies. The ACF can be measured `locally', and its anisotropy is caused by the tidal gravitational field of the deflecting mass distribution in the foreground of these faint background galaxies. Since the method does not require individual galaxy detection, it can be used to measure the shear of extremely faint galaxies which are not detectable individually, but are present in the noise. The shear estimated from the ACF of the noise provides an independent measurement which can be compared to the shear obtained from the distortion of individual galaxy images. Combining these two independent estimates clearly increases the sensitivity of shear measurements. In addition, our method may allow to determine the local magnification caused by the deflector if the auto-correlation function is caused by a large number density of faint galaxies; in this case, the intrinsic ACF may provide a `standard source' with respect to which shear and magnification can be obtained. Applications to real and synthetic data are shown and the feasibility of our new method is demonstrated. In particular, we present the shear maps obtained with our method for the double QSO 2345+007 and the cluster Cl0024+16 and compare them to published shear maps.

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arXiv1995

V/Vmax statistic and Neo-Classic Cosmological Tests

A new cosmological test is derived, based on the distribution of individual V/Vmax in a complete redshift-limited sample of distant objects. The fundamental assumption is that, in any bin of absolute luminosity, individual V/Vmax are required to be uniformly spread over the [0,1] range. This condition of uniformity allows a likelihood function to be computed from the Kolmogorov- Smirnov probabilities of each bin. Monte-Carlo simulations show that the test is mostly sensitive to the density parameter, but under certain conditions, it also sets constraints on the space curvature and, to a lower extent, on the cosmological constant. The test is then applied to the UVX sample of Boyle et al. (1990). A low matter density, and a flat Universe without cosmological constant, are rejected: 0.2<Omega<0.8 within the 95% confidence level.

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arXiv1995

Pure Luminosity Evolution Hypothesis for QSOs: From Luminosity Functions to Synthetic Catalogues

This paper describes the simulation of realistic Monte-Carlo extragalactic catalogues, aimed at comparing the behaviour of cosmological tests versus input parameters. QSO catalogues are built on a Luminosity Function derived from data through suitable computation of individual maximum volumes in complete (but magnitude- and redshift-limited) samples requiring neither of redshift nor of apparent magnitude histogram. The values of the evolution parameter are derived for various cosmologies, corresponding to =1/2 in the sample of 400 Ultra-Violet Excess (UVX) QSOs (Boyle et al 1990). The various luminosity functions are compared, both for the whole sample and in redshift bins. An evolution characteristic time is defined and computed, depending strongly on the cosmology, but practically constant when expressed in terms of the age of the Universe. Algorithms are given for producing unbiased or biased catalogues based on the null hypothesis that the objects are uniformly distributed in volume but suffer Pure Luminosity Evolution.

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