arXiv subjects

J. -C. Cuillandre

Publications and source records attributed to J. -C. Cuillandre.

108 records · Page 6Linked to original sources

arXiv2004

Mass and Light in the Supercluster of galaxies : MS0302+17

We investigate the supercluster MS0302+17 (z~0.42) using weak lensing analysis and deep wide field CFH12k BVR photometry. Using (B-V) - (V-R) evolution tracks we identify supercluster early-types members. We derive a R band weak lensing background galaxies sample. We compute the correlations functions of light and mass and show that "light traces mass on supercluster scales". The zeta-statistics applied in cluster centers and global correlation analyses over the whole field converge toward the simple relation M/L_B=300+/-30. This independently confirms the earlier results obtained by Kaiser et al.(1998). We model dark matter halos around each galaxy by truncated isothermal spheres and find the linear relation M L still holds. However, their averaged halo truncation radius is s* ~< 200 kpc close to clusters cores, whereas it reaches a lower limit of ~ 300 kpc at the periphery. This change of s_* as function of radial distance gives indications on tidal stripping but the lack of informations on the late-type galaxies sample prevents us to separate contributions. Though all the data at hands are consistent with "mass is traced by light from early-type galaxies", we are not able to describe in details the contributions of late type galaxies. We however found it to be small.

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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

Discovery of a z = 6.17 galaxy from CFHT and VLT observations

We report the discovery of a galaxy at a redshift z = 6.17 identified from deep narrow band imaging and spectroscopic follow-up in one of the CFHT-VIRMOS deep survey fields at 0226-04. In addition to the existing deep BVRI images of this field, we obtained a very deep narrow band image at 920 nm with the aim of detecting Lyalpha emission at redshift ~ 6.5. Spectroscopic follow-up of some of the candidates selected on the basis of their excess flux in the NB920 filter was performed at the VLT-UT4 with the FORS2 instrument. For one object a strong and asymmetric emission line associated with a strong break in continuum emission is identified as Lyalpha at z = 6.17. This galaxy was selected from its continuum emission in the 920 nm filter rather than for its Lyalpha emission, in effect performing a Lyman Break detection at z = 6.17. We estimate a star formation rate of several tens of M/yr for this object, with a velocity dispersion 400 km/s. The spectroscopic follow-up of other high $z$ galaxy candidates is on-going.

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arXiv2003

The z<=0.1 Surface Brightness Distribution

The surface brightness distribution (SBD) function describes the number density of galaxies as measured against their central surface brightness. Because detecting galaxies with low central surface brightnesses is both time-consuming and complicated, determining the shape of this distribution function can be difficult. In a recent paper Cross, et al. suggested a bell-shaped SBD disk-galaxy function which peaks near the canonical Freeman value of 21.7 and then falls off significantly by 23.5 B mag arcsec-2. This is in contradiction to previous studies which have typically found flat (slope=0) SBD functions out to 24 - 25 B mag arcsec^-2 (the survey limits). Here we take advantage of a recent surface-brightness limited survey by Andreon & Cuillandre which reaches considerably fainter magnitudes than the Cross, et.al sample (M_B reaches fainter than -12 for Andreon & Cuillandre while the Cross, et.al sample is limited to M_B < -16) to re-evaluate both the SBD function as found by their data and the SBD for a wide variety of galaxy surveys, including the Cross, et al. data. The result is a SBD function with a flat slope out through the survey limits of 24.5 B mag arcsec^-2, with high confidence limits.

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arXiv2002

The lower mass function of young open clusters

We report new estimates for the lower mass function of 5 young open clusters spanning an age range from 80 to 150 Myr. In all studied clusters, the mass function across the stellar/substellar boundary (~0.072 Mo) and up to 0.4 Mo is consistent with a power-law with an exponent alpha of -0.5 +/- 0.1, i.e., dN/dM ~ M**(-0.5).

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arXiv2001

Dissecting the luminosity function of the Coma cluster of galaxies using CFHT wide field images

[Abridged] We determined the luminosity function (LF) of the Coma cluster galaxies selected by luminosity, and the LF bi-variate in central brightness. The Coma cluster and control fields were imaged using the CFH12K (42x28 arcmin) and UH8K (28x28 arcmin) wide-field cameras at the CFHT. Selected HST images were used for testing. Quantities were derived from measurements in at least two colors, which have the following features: (1) Galaxies as faint as three times the luminosity of the brightest globular clusters are in the completeness region of our data. (2) We have a complete census (in the explored region) of low surface brightness galaxies with central surface brightness galaxies almost as low as the faintest so far cataloged ones. (3) The explored area is among the largest ever sampled with CCDs at comparable depth for any cluster of galaxies. (4) The error budget includes all sources of errors known to date. Using HST images we also discovered that blends of globular clusters, not resolved in individual components due to seeing, look like dwarf galaxies when observed from the ground and are numerous and bright. The derived Coma LF is relatively steep (alpha=-1.4) over the 11 magnitudes sampled, but the slope and shape depend on color. A large population of faint low surface brightness galaxies was discovered, representing the largest contributor (in number) to the LF at faint magnitudes. We found a clear progression for a faintening of the LF from high surface brightness galaxies (mu~20 mag/arcsec2) to galaxies of very faint central brightnesses (mu~24.5 mag/arcsec2), and some evidence for a steepening. Compact galaxies, usually classified as stars and therefore not included in the LF, are found to be a minor population in Coma.

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arXiv2001

Four Brown Dwarfs in the Taurus Star-Forming Region

We have identified four brown dwarfs in the Taurus star-forming region. They were first selected from $R$ and $I$ CCD photometry of 2.29 square degrees obtained at the Canada-France-Hawaii Telescope. Subsequently, they were recovered in the 2MASS second incremental data release point source catalog. Low-resolution optical spectra obtained at the William Herschel telescope allow us to derive spectral types in the range M7--M9. One of the brown dwarfs has very strong H$α$ emission (EW=-340 Å). It also displays Br$γ$ emission in an infrared spectrum obtained with IRCS on the Subaru telescope, suggesting that it is accreting matter from a disk. The \ion{K}{1} resonance doublet and the \ion{Na}{1} subordinate doublet at 818.3 and 819.5 nm in these Taurus objects are weaker than in field dwarfs of similar spectral type, consistent with low surface gravities as expected for young brown dwarfs. Two of the objects are cooler and fainter than GG Tau Bb, the lowest mass known member of the Taurus association. We estimate masses of only 0.03 M$_\odot$ for them. The spatial distribution of brown dwarfs in Taurus hints to a possible anticorrelation between the density of stars and the density of brown dwarfs.

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arXiv2001

Cosmic Shear Statistics and Cosmology

We report a measurement of cosmic shear correlations using an effective area of 6.5 sq. deg. of the VIRMOS deep imaging survey in progress at the Canada-France-Hawaii Telescope. We measured various shear correlation functions, the aperture mass statistic and the top-hat smoothed variance of the shear with a detection significance exceeding 12 sigma for each of them. We present results on angular scales from 3 arc-seconds to half a degree. The consistency of different statistical measures is demonstrated and confirms the lensing origin of the signal through tests that rely on the scalar nature of the gravitational potential. For Cold Dark Matter models we find $σ_8 Ω_0^{0.6}=0.43^{+0.04}_{-0.05}$ at the 95% confidence level. The measurement over almost three decades of scale allows to discuss the effect of the shape of the power spectrum on the cosmological parameter estimation. The degeneracy on sigma_8-Omega_0 can be broken if priors on the shape of the linear power spectrum (that can be parameterized by Gamma) are assumed. For instance, with Gamma=0.21 and at the 95% confidence level, we obtain 0.6 0.65 and Omega_0<0.4 for flat (Lambda-CDM) models. From the tangential/radial modes decomposition we can set an upper limit on the intrinsic shape alignment, which was recently suggested as a possible contribution to the lensing signal. Within the error bars, there is no detection of intrinsic shape alignment for scales larger than 1'.

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arXiv2000

Terapixel Surveys for Cosmic Shear

The recent detections of cosmic shear signal announced by several groups have demonstrated the feasibility of this challenging program and convinced astro- nomers of its potential for cosmology. Cosmic shear analysis demands to handle Gigabytes of data in order to probe several square degrees in subarcsecond deep imaging mode. The success of these surveys is sensitive to the designs of the observation strategy, the organization of the data reduction pipelines and the links of the data base with surveys like X-ray or spectroscopic follow up. We describe the cosmic shear surveys we have carried out at the VLT and at CFHT and the way we handle this huge data set in a more general context including the VIRMOS and the XMM-LSS surveys, and the future CMB surveys.

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arXiv2000

Dissecting the luminosity function of the Coma cluster of galaxies by means of CFHT wide field images

By means of wide-field (42x28 arcmin) CCD images of the Coma cluster of galaxies and of control fields, taken at the Canada-France-Hawaii telescope with the CFH12K and UH8K cameras, we determine the luminosity function bi-variate in central brightness. We found a clear progression for a steeping and weakening of the FL going from high surface brightness galaxies (mu~20$ mag/arcsec2) to galaxies of very-faint central brightnesses (mu 24.5 mag/arcsec2). Compact galaxies, usually rejected in the star/galaxy classification, are found to be a minor population in Coma. A huge population of low surface brightness galaxies red and faint are discovered, representing the largest contributor to the LF at faint magnitudes. Among them, there could be the remnant of high redshift starbursting galaxies responsible for the Butcher-Oemler effect.

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arXiv2000

Cosmic Shear and Clusters of Galaxies

The first detections of cosmic shear signal reported recently by 4 independent groups cover angular scales between one and 10 arcmin. On those scales, the cosmic shear is a signature of non-linear perturbations, like groups and clusters of galaxies. We present the results obtained by our team on CFHT and on the VLT and discuss its impact for the analysis of cluster abundances and cosmology

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arXiv2000

The Coma cluster luminosity function from ultraviolet to near-infrared

[Abridged] The Coma cluster luminosity function (LF) from ultraviolet (2000 AA) to the near-infrared (H band) is summarized. In the UV the LF is very steep, much steeper than in the optical. The steep Coma UV LF implies that faint and bright galaxies give similar contributions to the total UV flux and to the total metal production rate. The Coma UV LF is dominated by star forming galaxies, not by massive and large galaxies. The optical Coma LF is relatively steep (alpha=-1.4) over the 11 magnitudes sampled. We found a clear steeping of the FL going from B to R bands, indicative of the presence of a large number of red dwarfs, as faint as three bright globular clusters. Furthermore, using Hubble Space Telescope images, we discover that blends of globular clusters, not resolved in individual components due to seeing, look like dwarf galaxies when observed from the ground and are numerous and bright. The existence of these fake extended sources increases the steepness of the LF at faint magnitudes, if not deal on. The near-infrared LF was computed on a near-infrared selected sample of galaxies which photometry is complete down to the typical dwarf (M^*+5) luminosity. The Coma LF can be described by a Schechter function with intermediate slope (alpha~-1.3), plus a dip at M_H~-22 mag. The shape of the Coma LF in H band is quite similar to the one found in the B band. The similarity of the LF in the optical and H bands implies that in the central region of Coma there is no new population of galaxies which is too faint to be observed in the optical band (because dust enshrouded, for instance), down to the magnitudes of dwarfs.

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arXiv2000

Cosmic Shear with the CFHT

We present results of our cosmic shear survey in progress at the Canada- France-Hawaii Telescope (CFHT). We analysed 1.7 sq. degrees of data, out of which we measured a significant correlation of galaxy shape-orientation over several arcmin scale. We present measurements of the variance of the shear $<γ^2>$ and of the correlation functions $ $, $ $. The signal is consistent with gravitational lensing by large scale structures predictions. The level of residual systematics after PSF correction is small compared to our measured signal. We outline several evolutions of our work by using additional data covering 9 sq. degrees.

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arXiv1999

Mass-detection of a matter concentration projected near the cluster Abell 1942: Dark clump or high-redshift cluster?

A weak-lensing analysis of wide-field $V$- and $I$-band images centered on the cluster Abell 1942 has uncovered a mass concentration $\sim 7$ arcminutes South of the cluster center. A statistical analysis shows that the detections are highly significant. No strong concentration of bright galaxies is seen at the position of the mass concentration, though a slight galaxy number overdensity and a weak extended X-ray source are present about 1' away from its center. From the spatial dependence of the tangential alignment around the center of the mass concentration, we inferred a lower bound on the mass inside a sphere of radius $0.5 h^{-1}$\ts Mpc of $1\times 10^{14}h^{-1}M_\odot$, much higher than crude mass estimates based on X-ray data. No firm conclusion can be inferred about the nature of the clump. If it were a high-redshift cluster, the weak X-ray flux would indicate that it had an untypically low X-ray luminosity for its mass; if the X-ray emission were physically unrelated to the mass concentration, this conclusion would be even stronger. The search for massive halos by weak lensing enables us for the first time to select halos based on their mass properties only and to detect new types of objects, e.g., dark halos. The mass concentration in the field of A1942 may be the first example of such a halo.

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arXiv1998

NGC 5907 revisited: a stellar halo formed by cannibalism?

We report on further observations of the luminous halo of NGC 5907. New V, I and B deep photometry confirms the existence of an extended stellar halo redder than the disk. Our data are consistent with a faint halo, or very thick disk, composed of a metal-rich old stellar population. We propose that it could be the remnant of a merged small elliptical, and we support our hypothesis with N-body simulations.

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arXiv1997

An optical and near-IR survey of nearby clusters of galaxies

We present an optical and near-infrared survey of galaxies in nearby clusters aimed at determining fundamental quantities of galaxies, such as multivariate luminosity function and color distribution for each Hubble type. The main characteristics of our survey are completeness in absolute magnitude, wide wavelength coverage and faint limiting magnitudes.

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arXiv1996

Wide-field CCD imaging at CFHT: the MOCAM example

We describe a new 4096x4096 pixel CCD mosaic camera (MOCAM) available at the prime focus of the Canada-France-Hawaii Telescope (CFHT). The camera is a mosaic of four 2048x2048$ Loral frontside-illuminated CCDs with 15 $μ$m pixels, providing a field of view of 14'x14' at a scale of 0.21''/pixel. MOCAM is equipped with B, V, R and I filters and has demonstrated image quality of 0.5''-0.6'' FWHM over the entire field. MOCAM will also be used with the CFHT adaptive optic bonnette and will provide a field of view of 90'' at a scale of 0.02 ''/pixel. MOCAM works within the CFHT Pegasus software environment and observers familiar with this system require no additional training to use this camera effectively. The technical details, the performance and the first images obtained on the telescope with MOCAM are presented. In particular, we discuss some important improvements with respect to the standard single-CCD FOCAM camera, such as multi-output parallel readout and dynamic anti-blooming. We also discuss critical technical issues concerning future wide-field imaging facilities at the CFHT prime focus in light of our experience with MOCAM and our recent experience with the even larger UH 8192x8192 pixel CCD mosaic camera.

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arXiv1996

V- and I-band observations of the halo of NGC 5907

Using long exposures taken in the V and I bands with a 4096$\times$4096 pixel CCD array at the prime focus of the Canada-France-Hawaii telescope, we have confirmed the discovery by Sackett et al. (1994) of a flat, faint luminous halo around the edge-on Sc galaxy NGC$\thinspace$5907. This halo is redder than the disk. Its nature is still an observational challenge. We suggest however that its color can only be accounted for by stars less massive than 0.8 $M_{\odot}$. Their total mass in NGC$\thinspace$5907 is very uncertain, but it might possibly account for the excess dynamical mass in this galaxy. Alternatively their distribution might trace the dark potential without contributing signifi- cantly to the mass. We give upper limits to the extinction by an hypothetical dust in the halo.

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