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Y. Mellier

Publications and source records attributed to Y. Mellier.

At least 217 records · Page 12Linked to original sources
arXiv2003

Early results from the VIMOS VLT Deep Survey

The VIMOS VLT Deep Survey (VVDS) is underway to study the evolution of galaxies, large scale structures and AGNs, from the measurement of more than 100000 spectra of faint objects. We present here the results from the first epoch observations of more than 20000 spectra. The main challenge of the program, the redshift measurements, is described, in particular entering the ``redshift desert'' in the range $1.5<z<3$ for which only very weak features are observed in the observed wavelength range. The redshift distribution of a magnitude limited sample brighter than $I_{AB}=24$ is presented for the first time, showing a peak at a low redshift $z\sim0.7$, and a tail extending all the way above $z=4$. The evolution of the luminosity function out to $z=1.5$ is presented, with the LF of blue star forming galaxies carrying most of the evolution, with L* changing by more than two magnitudes for this sub-sample.

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arXiv2003

The Canada-France deep fields survey-II: Lyman-break galaxies and galaxy clustering at z~3

(abridged) We present a large sample of z~3 U- band dropout galaxies extracted from the Canada-France deep fields survey (CFDF). Our catalogue covers an effective area of ~1700 arcmin^2 divided between three large, contiguous fields separated widely on the sky. To IAB=24.5, the survey contains 1294 Lyman-break candidates, in agreement with previous measurements by other authors. Based on comparisons with spectroscopic observations and simulations, we estimate that our sample of Lyman-break galaxies is contaminated by stars and interlopers at no more than ~30%. We find that ω(θ) is well fitted by a power-law of fixed slope, γ=1.8, even at small (θ<10'') angular separations. In two of our three fields, we are able to fit simultaneously for both the slope and amplitude and find a slope γ~ 1.81. Our data marginally indicates in one field (at a 3 σlevel) that the Lyman-break correlation length r_0 depends on sample limiting magnitude: brighter Lyman-break galaxies are more clustered than fainter ones. For the entire CFDF sample, assuming a fixed slope γ= 1.8 we find r_0 = (5.9\pm0.5)h^{-1} Mpc. Using these clustering measurements and prediction for the dark matter density field, we derive a linear bias of b = 3.5 +/- 0.3. Finally we show that the dependence of the correlation length with the surface density of Lyman-break galaxies is in good agreement with a simple picture where more luminous galaxies are hosted by more massive dark matter halos with a simple one-to-one correspondence.

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arXiv2003

The VIRMOS deep imaging survey II: CFH12K BVRI optical data for the 0226-04 deep field

(abridged) In this paper we describe in detail the reduction, preparation and reliability of the photometric catalogues which comprise the 1.2 deg^2 CFH12K-VIRMOS deep field. The survey reaches a limiting magnitude of BAB~26.5, VAB~26.2, RAB~25.9 IAB~25.0 and contains 90,729 extended sources in the magnitude range 18.0<IAB<24.0. We demonstrate our catalogues are free from systematic biases and are complete and reliable down these limits. We estimate that the upper limit on bin-to-bin systematic photometric errors for the I- limited sample is ~10% in this magnitude range. We estimate that 68% of the catalogues sources have absolute per co-ordinate astrometric uncertainties less than ~0.38" and ~0.32" (alpha,delta). Our internal (filter-to-filter) per co-ordinate astrometric uncertainties are 0.08" and 0.08" (alpha,delta). We quantify the completeness of our survey in the joint space defined by object total magnitude and peak surface brightness. Finally, we present numerous comparisons between our catalogues and published literature data: galaxy and star counts, galaxy and stellar colours, and the clustering of both point-like and extended populations. In all cases our measurements are in excellent agreement with literature data to IAB<24.0. This combination of depth and areal coverage makes this multi-colour catalogue a solid foundation to select galaxies for follow-up spectroscopy with VIMOS on the ESO-VLT and a unique database to study the formation and evolution of the faint galaxy population to z~1 and beyond.

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arXiv2003

The VIRMOS deep imaging survey: I. overview and survey strategy

This paper presents the CFH12K-VIRMOS survey: a deep B, V, R and I imaging survey in four fields totalling more than 17 deg^2, conducted with the 30x40 arcmin^2 field CFH-12K camera. The survey is intended to be a multi-purpose survey used for a variety of science goals, including surveys of very high redshift galaxies and weak lensing studies. Four high galactic latitude fields, each 2x2 deg^2, have been selected along the celestial equator: 0226-04, 1003+01, 1400+05, and 2217+00. The 16 deg^2 of the "wide" survey are covered with exposure times of 2h, 1.5h, 1h, 1h, while the 1.3x1 deg^2 area of the "deep" survey at the center of the 0226-04 field is covered with exposure times of 7h, 4.5h, 3h, 3h, in B,V,R and I respectively. The data is pipeline processed at the Terapix facility at the Institut d'Astrophysique de Paris to produce large mosaic images. The catalogs produced contain the positions, shape, total and aperture magnitudes for the 2.175 million objects. The depth measured (3sigma in a 3 arc-second aperture) is I_{AB}=24.8 in the ``Wide'' areas, and I_{AB}=25.3 in the deep area. Careful quality control has been applied on the data as described in joint papers. These catalogs are used to select targets for the VIRMOS-VLT Deep Survey, a large spectroscopic survey of the distant universe (Le Fèvre et al., 2003). First results from the CFH12K-VIRMOS survey have been published on weak lensing (e.g. van Waerbeke & Mellier 2003). Catalogs and images are available through the VIRMOS database environment under Oracle ({\tt http://www.oamp.fr/virmos}). They will be open for general use on July 1st, 2003.

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arXiv2003

A radial mass profile analysis of the lensing cluster MS2137-23

We reanalyze the strong lens modeling of the cluster of galaxies MS2137-23 using a new data set obtained with the ESO VLT. We found the photometric redshifts of the two main arc systems are both at z=1.6. After subtraction of the central cD star light of the HST image we found that only one object lying underneath has the expected properties of the fifth image associated to the tangential arc. We improve the previous lens modelings of the central dark matter distribution of the cluster, using an isothermal model with a core (IS) and the NFW-like model with a cusp. Without the fifth image, the arc properties together with the shear map profile are equally well fit by the and by an IS and a sub-class of generalized-NFW mass profiles having inner slope power index in the range 0.7<alpha<1.2. Adding new constrains provided by the fifth image favors IS profiles that better predict the fifth image properties. A model including cluster galaxy perturbations or the the stellar mass distribution does not change our conclusions but imposes the M/L_I of the cD stellar component is below 10 at a 99% confidence level. Using our new detailed lensing model together with Chandra X-ray data and the cD stellar component we finally discuss intrinsic properties of the gravitational potential. Whereas X-ray and dark matter have a similar shape at various radius, the cD stellar isophotes are twisted by 13 deg. The sub- arc-second azimuthal shift we observe between the radial arc position and the predictions of elliptical models correspond to what is expected from a mass distribution twist. This shift may result from a projection effect of the cD and the cluster halos, thus revealing the triaxiality of the system.

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arXiv2002

Cosmic Shear Review

We present an overview of the cosmic shear results obtained so far. We focus on the 2-point statistics only. Evidences supporting the cosmological origin of the measured signal are reviewed, and issues related to various systematics are discussed.

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arXiv2002

Prospects for weak lensing/cosmic shear with VLTs

The present status of weak lensing analyses of clusters of galaxies and of cosmic shear surveys are presented and discussed. We focus on the impact of very large telescopes on present-day and future surveys and compare their potential with HST or wide field 4 meter telescopes.

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arXiv2002

Wide-field cosmic shear surveys

We present the current status of cosmic shear based on all surveys done so far. Taken together, they cover more about 70 deg$^2$ and concern more than 3 million galaxies with accurate shape measurement. Theoretical expectations, observational results and their cosmological interpretations are discussed in the framework of standard cosmology and CDM scenarios. The potentials of the next generation cosmic shear surveys are discussed.

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arXiv2002

Detection of non-Gaussian Signatures in the VIRMOS-DESCART Lensing Survey

We have detected non-Gaussian signatures in the VIRMOS-DESCART weak lensing survey from a measurement of the three-point shear correlation function, following the method developed by Bernardeau et al. (2002). We obtain a 2.4-sigma signal over four independent angular bins, or equivalently, a 4.9-sigma confidence level detection with respect to measurements errors on scale of about 2 to 4 arcmin. The amplitude and the shape of the signal are consistent with theoretical expectations obtained from ray-tracing simulations. This result supports the idea that the measure corresponds to a cosmological signal due to the gravitational instability dynamics. Its properties could be used to put constraints on the cosmological parameters, in particular on the density parameter of the Universe, but the error level as well as the cosmic variance are still too large to permit secure conclusions.

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arXiv2002

Patterns in the weak shear 3-point correlation function

We explore the scale and angular dependence of the cosmic shear three-point correlation function. The shear field is found to have a much more complex three-point function than the convergence field, but it also exhibits specific motifs which draw signatures of gravitational lensing. Exact shear patterns are inferred analytically for some geometrical shear triplets configurations, when simple interpretations can be derived. A more complete description of their geometrical properties has then been carried out from ray-tracing numerical simulations and simple models. These patterns reveal typical features that can be utilized for non-gaussian signal detection in cosmic shear surveys. We test the robustness of these properties against complex noise statistics and non-trivial survey topologies. From these conclusive checks, we predict that the VIRMOS-DESCART survey should allow a detection of a non-gaussian signal with a comfortable significance for a low matter density Universe.

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arXiv2002

B-modes in cosmic shear from source redshift clustering

Weak gravitational lensing by the large scale structure can be used to probe the dark matter distribution in the Universe directly and thus to probe cosmological models. The recent detection of cosmic shear by several groups has demonstrated the feasibility of this new mode of observational cosmology. In the currently most extensive analysis of cosmic shear, it was found that the shear field contains unexpected modes, so-called B-modes, which are thought to be unaccountable for by lensing. B-modes can in principle be generated by an intrinsic alignment of galaxies from which the shear is measured, or may signify some remaining systematics in the data reduction and analysis. In this paper we show that B-modes in fact {\it are produced} by lensing itself. The effect comes about through the clustering of source galaxies, which in particular implies an angular separation-dependent clustering in redshift. After presenting the theory of the decomposition of a general shear field into E- and B-modes, we calculate their respective power spectra and correlation functions for a clustered source distribution. Numerical and analytical estimates of the relative strength of these two modes show that the resulting B-mode is very small on angular scales larger than a few arcminutes, but its relative contribution rises quickly towards smaller angular scales, with comparable power in both modes at a few arcseconds. The relevance of this effect with regard to the current cosmic shear surveys is discussed.

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arXiv2002

Cosmological Weak Lensing

We present the current status of cosmic shear studies and their implications on cosmological models. Theoretical expectations and observational results are discussed in the framework of standard cosmology and CDM scenarios. The potentials of the next generation cosmic shear surveys are discussed.

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arXiv2002

Cosmic Shear: The Dark Side of the Universe

We discuss the present status and future prospects for cosmic shear observations and their cosmological constraints. We review the evidences supporting the cosmological origin of the measured signal, and discuss the possible problems coming from intrinsic alignment and from the actual limitations of theoretical predictions.

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arXiv2002

Likelihood Analysis of Cosmic Shear on Simulated and VIRMOS-DESCART Data

We present a maximum likelihood analysis of cosmological parameters from measurements of the aperture mass up to 35 arcmin, using simulated and real cosmic shear data. A four-dimensional parameter space is explored which examines the mean density Ω_M, the mass power spectrum normalization σ_8, the shape parameter Γand the redshift of the sources z_s. Constraints on Ω_M and σ_8 (resp. Γand z_s) are then given by marginalizing over Γand z_s (resp. Ω_M and σ_8). For a flat LCDM cosmologies, using a photometric redshift prior for the sources and Γ\in [0.1,0.4], we find σ_8=(0.57\pm0.04) Ω_M^{(0.24\mp 0.18) Ω_M-0.49} at the 68% confidence level (the error budget includes statistical noise, full cosmic variance and residual systematic). The estimate of Γ, marginalized over Ω_M \in [0.1,0.4], σ_8 \in [0.7,1.3] and z_s constrained by photometric redshifts, gives Γ=0.25\pm 0.13 at 68% confidence. Adopting h=0.7, a flat universe, Γ=0.2 and Ω_m=0.3 we find σ_8=0.98 \pm0.06 . Combined with CMB, our results suggest a non-zero cosmological constant and provide tight constraints on Ω_M and σ_8. We finaly compare our results to the cluster abundance ones, and discuss the possible discrepancy with the latest determinations of the cluster method. In particular we point out the actual limitations of the mass power spectrum prediction in the non-linear regime, and the importance for its improvement.

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arXiv2001

Tracing Matter with Weak Lensing Surveys

Gravitational weak lensing maps the location of (dark) matter at all scales. The lens-induced distortion field traces gravity fields and can be used to reconstruct the mass distribution in galaxies, groups, clusters of galaxies or large-scale structures. From these reconstructions, one can in principle recover where the matter is, what are its properties and how it is coupled with light and baryons. In the following, we review the present status of weak lensing analysis and discuss the most recent results regarding matter properties in the universe.

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arXiv2001

The Canada-France deep fields survey-I: 100,000 galaxies, 1 deg^2: a precise measurement of ω(θ) to IAB~25

(abridged) Using the UH8K mosaic camera, we have measured the angular correlation function ω(θ) for 100,000 galaxies over four widely separated fields totalling ~1°^2 and reaching IAB~25.5. With this sample we investigate the dependence of ω(θ) at 1', A_ω(1'), on sample median IAB magnitude in the range 19.5 1. Models with ε~0 cannot simultaneously match both bright and faint measurements of A_ω(1`). We show how this result is a natural consequence of the ``bias-free'' nature of the εformalism and is consistent with the field galaxy population in the range 22.0<IAB<24.0 being dominated by galaxies of low intrinsic luminosity.

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arXiv2001

VLT Spectroscopy of Galaxies Lensed by Abell AC114: Implication for the Mass Model and the Study of Low-Luminosity Galaxies at High-Redshift

We present the first results of a spectroscopic survey of faint lensed galaxie s in the core of the galaxy cluster AC114 (z=0.312) obtained from observations w ith the FORS1 spectrograph mounted on the VLT-Antu. The galaxies were chose n in areas close to the high-z critical lines predicted by the gravitational lens model of Natarajan et al (NKSE, 1998) for this cluster, according to both lensing and photometric redshift criteria. All the target galaxies are found to correspond to background galaxies with redshifts values in the [0.7, 3.5] interval. Our spectroscopic observations confirm the predicted lensing redshifts for 3 of the multiple-image galaxies, and together with predictions of the NKSE model led to the discovery of a new 5-image configuration at redshift z=3.347. A revised NKSE model, compatible with the redshift of this new multiple-image system, was generated and employed to calculate the gravitational amplifications of all the observed galaxies. The galaxies corresponding to the multiple-image systems are found to be intrinsically fainter, between 0.5 and 1.5 magnitudes, than the limiting magnitudes of existing blank field studies. When all the observed background galaxies are considered, the resulting intrinsic absolute magnitudes range from M_B~-22 to -19. Therefore, a large gain in sensitivity towards low luminosity high-z objects can actually be obtained, in agreement with theoretical expectations. This method can be used advantageously to probe the high redshift Universe and, in particular, its application to an ensemble of massive cluster cores could constraint the faint end of luminosity function of high redshift galaxies.

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