arXiv subjects

G. Soucail

Publications and source records attributed to G. Soucail.

At least 55 records · Page 3Linked to original sources

arXiv2005

A CFH12k lensing survey of X-ray luminous galaxy clusters - I: Weak lensing methodology

We present the weak lensing methodology applied to our multi-colour imaging survey of X-ray luminous galaxy clusters conducted with the wide field CFH12k camera. This method, which is converting a fully reduced CFH12k image into cluster mass constraints, is done in two steps that we explain in detail: (1) determination of the "true" shape of faint (lensed) galaxies which involves: object detection strategy, point spread function (PSF) determination, galaxy shapes measurements with errors; (2) conversion of the faint galaxies catalogue into useful mass constraints which is done by different lensing techniques using 1D and/or 2D mass estimates. Finally, we compare the cluster mass model to the light distribution of cluster members as observed on our imaging data. To illustrate the method, we apply it to the well studied cluster Abell 1689 (z=0.184). In this cluster, we detect the gravitational shear signal to the edge of the image at 3 sigma significance. The two-dimensional mass reconstruction has a ~10 sigma significance mass peak centered on the brightest cluster galaxy. The weak lensing constraints are well fitted by a NFW mass profile with $M_{200} = 14.1^{+6.3}_{-4.7}\times 10^{14} M_\sun$, and $c = 3.5^{+0.5}_{-0.3}$ (chi^2=0.33), or by a power law (PL) profile with q=0.75 +- 0.07 and theta_E = 14.6"+-0.3" (chi^2=0.64). The mass-to-light ratio is found to be almost constant with radius with a mean value of M/L_R = 150 h (M/L)_\sun. We compare these results to other weak lensing analyses of Abell 1689 presented in the literature and find good agreements in terms of the shear measurement as well as the final mass estimate.

astro-ph↗

arXiv2004

XMM-Newton study of the lensing cluster of galaxies CL0024+17

We present a detailed gravitational mass measurement based on the XMM-Newton imaging spectroscopy analysis of the lensing cluster of galaxies CL0024+17 at z=0.395. The emission appears approximately symmetric. However, on the scale of r~3.3' some indication of elongation is visible in the northwest-southeast (NW-SE) direction from the hardness ratio map (HRM). Within 3', we measure a global gas temperature of 3.52\pm0.17 keV, metallicity of 0.22\pm0.07, and bolometric luminosity of 2.9\pm0.1 \times 10^{44} h^{-2}_{70} erg/s. We derive a temperature distribution with an isothermal temperature of 3.9 keV to a radius of 1.5' and a temperature gradient in the outskirts (1.3<r<3'). Under the assumption of hydrostatic equilibrium, we measure gravitational mass and gas mass fraction to be M_{200}=2.0\pm0.3 \times 10^{14} h_{70}^{-1} M_{\odot} and f_{\rm gas}=0.20\pm0.03 h^{-3/2}_{70} at r_{200}=1.05 h^{-1}_{70} Mpc using the observed temperature profile. The complex structure in the core region is the key to explaining the discrepancy in gravitational mass determined from XMM-Newton X-ray observations and HST optical lensing measurements.

astro-ph↗

arXiv2004

Variable stars towards the bulge of M31: the AGAPE catalogue

We present the AGAPE astrometric and photometric catalogue of 1579 variable stars in a 14'x10' field centred on M31. This work is the first survey devoted to variable stars in the bulge of M31. The R magnitudes of the objects and the B-R colours suggest that our sample is dominated by red long-period variable stars (LPV), with a possible overlap with Cepheid-like type II stars. Twelve nova candidates are identified. Correlations with other catalogues suggest that 2 novae could be recurrent novae and provide possible optical counterparts for 2 supersoft X-ray sources candidates observed with Chandra.

astro-ph↗

arXiv2004

Multiple-Images in the Cluster Lens Abell 2218: Constraining the Geometry of the Universe ?

In this Letter we present a detailed study of the lensing configuration in the cluster Abell 2218. Four multiple-images systems with measured spectroscopic redshifts have been identified in this cluster. These multiple images are very useful to constrain accurately the mass distribution in the cluster core, but they are also sensitive to the value of the geometrical cosmological parameters of the Universe. Using a simplified maximum likelihood analysis we find 0 < Omega_M < 0.30 assuming a flat Universe, and 0 < Omega_M < 0.33 and w < -0.85 for a flat Universe with dark energy. Interestingly, an Einstein-de Sitter model is excluded at more than 4sigma. These constraints are consistent with the current constraints derived with CMB anisotropies or supernovae studies. The proposed method constitutes an independent test of the geometrical cosmological parameters of the Universe and we discuss the limits of this method and this particular application to Abell 2218. Application of this method with more sophisticated tools and to a larger number of clusters or with more multiple images constraints, will put stringent constraints on the geometrical cosmological parameters.

astro-ph↗

arXiv2003

The galaxy population of the z=1 cluster of galaxies MG2016+112

A photometric redshift analysis of galaxies in the field of the wide-separation gravitational lens MG2016+112 reveals a population of 69 galaxies with photometric redshifts consistent with being in a cluster at the redshift of the giant elliptical lensing galaxy, z=1.00. The Ks-band luminosity function of the cluster galaxies is well represented by the Schechter function with a characteristic magnitude Ks*=18.90 (-0.57/+0.45) and faint-end slope alpha=-0.60 (-0.33/+0.39), consistent with what is expected for a passively evolving population of galaxies formed at high redshift, zf>2. From the total Ks-band flux of the cluster galaxies and a dynamical estimate of the total mass of the cluster, the restframe Ks-band mass-to-light ratio of the cluster is derived to be M/L=27(-17/+64)(h_50)(M/L)_{sun}, in agreement with the upper limit derived earlier from Chandra X-ray observations and the value derived locally in the Coma cluster. The cluster galaxies span a red sequence with a considerable scatter in the colour-magnitude diagrams, suggesting that they contain young stellar populations in addition to the old populations of main-sequence stars that dominate the Ks-band luminosity function. This is in agreement with spectroscopic observations which show that 5 out of the 6 galaxies in the field confirmed to be at the redshift of the lensing galaxy have emission lines. The projected spatial distribution of the cluster galaxies is filamentary-like rather than centrally concentrated around the lensing galaxy, and show no apparent luminosity segregation. A handful of the cluster galaxies show evidence of merging/interaction. The results presented in this paper suggest that a young cluster of galaxies is assembling around MG2016+112.

astro-ph↗

arXiv2002

Spectroscopy of the neighboring massive clusters Abell 222 and Abell 223

We present a spectroscopic catalog of the neighboring massive clusters Abell 222 and Abell 223. The catalog contains the positions, redshifts, R magnitudes, V-R color, as well as the equivalent widths for a number of lines for 183 galaxies, 153 of them belonging to the A 222 and A 223 system. We determine the heliocentric redshifts to be z=0.2126+/-0.0008 for A 222 and z=0.2079+/-0.0008 for A 223. The velocity dispersions of both clusters in the cluster restframe are about the same: sigma = 1014^{+90}_{-71} km/s and sigma = 1032^{+99}_{-76} km/s for A 222 and A 223, respectively. While we find evidence for substructure in the spatial distribution of A 223, no kinematic substructure can be detected. From the red cluster sequence identified in a color--magnitude--diagram we determine the luminosity of both clusters and derive mass--to--light ratios in the R--band of (M/L)_A222 = (202+/-43) h_70 M_{su}n/L_{sun} and (M/L)_A223 = (149+/-33) h_70 M_{sun}/L_{sun}. Additionally we identify a group of background galaxies at z ~ 0.242.

astro-ph↗

arXiv2002

Constraining the Cosmological Parameters using Strong Lensing

We investigate the potentiality of using strong lensing clusters to constrain the cosmological parameters Omega_m and Omega_lambda. The existence of a multiple image system with known redshift allows, for a given (Omega_m, Omega_lambda) cosmology, absolute calibration of the total mass deduced from lens modelling. Recent Hubble Space Telescope (HST) observations of galaxy clusters reveal a large number of multiple images, which are predicted to be at different redshifts. If it is possible to measure spectroscopically the redshifts of many multiple images then one can in principle constrain (Omega_m,Omega_lambda) through ratios of angular diameter distances, independently of any external assumptions. For a regular/relaxed cluster observed by HST with 3 multiple image systems, each with different spectroscopic redshifts, we show by analytic calculation that the following uncertainties can be expected: Omega_m=0.30 +/- 0.11, Omega_lambda=0.70 +/- 0.23 or Omega_m=1.00 +/- 0.17, Omega_lambda=0.00 +/- 0.48 for the two most popular world models. Numerical tests on simulated data confirm these good constraints, even in the case of more realistic cluster potentials, such as bimodal clusters, or when including perturbations by galaxies. To investigate the sensitivity of the method to different mass profiles, we also use an analytic ``pseudo-elliptical'' Navarro, Frenk & White profile in the simulations. These constraints can be improved if more than 3 multiple images with spectroscopic redshifts are observed, or by combining the results from different clusters. Some prospects on the determination of the cosmological parameters with gravitational lensing are given.

astro-ph↗

arXiv2002

Constraints on (Omega_M0, Omega_Lambda) from strong lensing in AC 114

We use a strong lensing inversion in the cluster of galaxies AC 114 to derive constraints on the cosmological parameters Omega_M0 and Omega_Lambda. If it is possible to measure spectroscopically the redshifts of many multiple images then one can in principle constrain (Omega_M0,Omega_Lambda) through ratios of angular diameter distances, independently of any external assumptions. Numerical tests on simulated data show rather good constraints from this test. We also use an analytic ``pseudo-elliptical'' NFW profile in the simulations, following the general new formalism we present. An application to AC 114 favors a flat Universe, an EdS model being marginally ruled out.

astro-ph↗

arXiv2001

Constraints on (Omega,Lambda) from strong lensing clusters

We use three strong lensing clusters to constrain the cosmological parameters Omega_m and Omega_lambda. Recent HST observations of galaxy clusters reveal a large number of multiple images, which are predicted to be at different redshifts. We showed in a previous work that if it is possible to measure spectroscopically the redshift of many multiple images then one can constrain (Omega_m,Omega_lambda) through ratios of angular diameter distances independently of any external assumptions. Using three strong lensing clusters, our combined results lead to tight constraints.

astro-ph↗

arXiv2000

Spectroscopic confirmation of a cluster of galaxies at z=1 in the field of the gravitational lens MG2016+112

We present new optical data on the cluster AX J2019+1127 identified by the X-ray satellite ASCA at z\sim 1 (Hattori et al. 1997). The data suggest the presence of a high-redshift cluster of galaxies responsible for the large separation triple quasar MG2016+112. Our deep photometry reveals an excess of z\sim 1 galaxy candidates, as already suspected by Benitez et al. (1999). Our spectroscopic survey of 44 objects in the field shows an excess of 6 red galaxies securely identified at z \sim 1, with a mean redshift of z =1.005 +/- 0.002. We estimate a velocity dispersion of σ= 771 (+430/-160) km s(-1) based on these 6 galaxies and a V-band mass-to-light ratio of 215 (+308/-77) h_50 M/L_sol. Our observations thus confirm the existence of a massive structure acting as the lens, which explains the unusual configuration of the triple quasar. Hence, there is no more need to invoke the existence of a ``dark cluster'' to understand this lens system.

astro-ph↗

arXiv2000

Exploring the gravitationally lensed system HE1104-1805: VLT spectroscopy of the lens at z=0.729

Using FORS2, mounted on Kueyen (UT2 of the VLT), we have obtained the redshift of the lensing galaxy in the gravitational lens system HE1104-1805. We measure z=0.729, in good agreement with previous estimates based on the time delay and the position of the lens on the fundamental plane. It also coincides with one of the metal line absorption systems that are seen in high resolution spectra of HE1104-1805.

astro-ph↗

arXiv2000

Constraining the cosmological parameters from gravitational lenses with several families of images

The knowledge of the redshift of multiple images in cluster-lenses allows to determine precisely the total projected mass within the Einstein radius. The observation of various multiple images in a same cluster is opening new possibilities to constrain the curvature of the universe. Indeed, although the influence of $Ω_m$ and $Ω_λ$ on the images formation is of the second order, observations of many multiple images at different redshifts formed by a regular cluster-lens should allow to constrain very accurately the mass distribution of the cluster and to start to be sensitive to the cosmological parameters entering the diameter angular distances. We present, analytical expressions and numerical simulations that allow us to compute the expected error bars on the cosmological parameters provided an HST/WFPC2 resolution image and spectroscopic redshifts for the multiple images. Numerical tests on simulated data confirm the rather small uncertainties we could obtain this way for the two popular cosmological world models: $Ω_m=0.3{\pm 0.24}$, $Ω_λ=0.7{\pm 0.5}$ or $Ω_m=1.{\pm 0.33}$, $Ω_λ=0.{\pm 1.2}$. Our method can be applied from now on, on real clusters.

astro-ph↗

arXiv2000

Probing the gravitational potential of a nearby lensing cluster Abell 2104

The cluster Abell 2104 is one of the lowest redshift clusters (z=0.153) known to have a gravitational lensing arc. We present detailed analysis of the cluster properties such as the gravitational potential using the X-ray data from ROSAT (HRI) and ASCA, as well as optical imaging and spectroscopic data from the CFHT. The cluster is highly luminous in the X-ray with a bolometric luminosity of Lx ~3x10^{45} ergs/s and a high gas temperature of ~10.4 keV. The X-ray emission extending out to at least a radius of 1.46 Mpc, displays significant substructure. The total mass deduced from the X-ray data under the assumption of hydrostatic equilibrium and isothermal gas, is found to be M_tot(r<1.46Mpc) ~(8.0 +/- 0.8)x10^{14} solar mass. The gas fraction within a radius of 1.46 Mpc is ~5-10%. The cluster galaxy velocity distribution has a dispersion of 1200 +/- 200 km/s with no obvious evidence for substructure. The total mass within 1.46 Mpc, deduced from Jean's equation using the observed galaxy number density distribution and velocity dispersion, is found to be \~6.8x10^{14} solar mass to ~2.6x10^{15} solar mass marginally consistent with the X-ray deduced total mass.

astro-ph↗

arXiv2000

Constraining (Ω_m,Ω_λ) from strong lensing

astro-ph↗

arXiv2000

X-ray observations and mass determinations in the cluster of galaxies Cl0024+17

We present a detailed analysis of the mass distribution in the rich and distant cluster of galaxies Cl0024+17. X-ray data come from both a deep ROSAT/HRI image of the field (Bohringer et al. 1999) and ASCA spectral data. Using a wide field CCD image of the cluster, we optically identify all the faint X-ray sources, whose counts are compatible with deep X-ray number counts. In addition we marginally detect the X-ray counter-part of the gravitational shear perturbation detected by Bonnet et al. (1994) at a 2.5 $σ$ level. A careful spectral analysis of ASCA data is also presented. In particular, we extract a low resolution spectrum of the cluster free from the contamination by a nearby point source located 1.2 arcmin from the center. The X-ray temperature deduced from this analysis is $T_X = 5.7 ^{+4.9}_{-2.1}$ keV at the 90% confidence level. The comparison between the mass derived from a standard X-ray analysis and from other methods such as the Virial Theorem or the gravitational lensing effect lead to a mass discrepancy of a factor 1.5 to 3. We discuss all the possible sources of uncertainties in each method of mass determination and give some indications on the way to reduce them. A complementary study of optical data is in progress and may solve the X-ray/optical discrepancy through a better understanding of the dynamics of the cluster.

astro-ph↗

arXiv1999

The X-ray Morphology of the Lensing Galaxy Cluster Cl0024+17

The paper reports the analysis of a very deep ROSAT HRI observation of the distant lensing cluster, CL0024+17. The morphology of the cluster is studied and the small core radius inferred from lensing analysis is confirmed. Constraints on the mass distribution are discussed.

astro-ph↗

arXiv1999

An ISOCAM Mid-IR Survey through Gravitationally Lensing Galaxy Clusters

We present imaging results and source counts from a deep ISOCAM cosmological survey at 15 microns, through gravitationally lensing galaxy clusters. We take advantage of the cluster gravitational amplification to increase the sensitivity of our survey. We detect a large number of luminous mid-IR sources behind the cluster lenses, down to very faint fluxes, which would have been unreachable without the gravitational lensing effect. These source counts, corrected for lensing distortion effects and incompleteness, are in excess of the predictions of no-evolution models that fit local IRAS counts. By integrating the 15 microns source counts from our counts limit, 30 microJy, to 50 mJy we estimate the resolved mid-IR background radiation intensity.

astro-ph↗

arXiv1999

Depletion curves of galaxy number counts behind cluster lenses

When the logarithmic slope of the galaxy counts is lower than 0.4 (this is the case in all filters at high magnitude), the magnification bias due to the lens makes the number density of objects decrease. Consequently, the radial distribution shows a typical depletion curve. We present simulations of depletion curves obtained for a variety of different lens models and we show how the model parameters affect the depletion area.

astro-ph↗