Aims: We perform a comprehensive study of the total massdistribution of the galaxy cluster RXC J2248.7-4431 (z = 0.348) with aset of high-precision strong lensing models which take advantage ofextensive spectroscopic information on many multiply lensed systems. Inthe effort to understand and quantify inherent systematics in parametricstrong lensing modelling we explore a collection of 22 models in whichwe use different samples of multiple image families differentparametrizations of the mass distribution and cosmological parameters. Methods: As input information for the strong lensing models weuse the Cluster Lensing And Supernova survey with Hubble (CLASH) imagingdata and spectroscopic follow-up observations with the VIsibleMulti-Object Spectrograph (VIMOS) and Multi Unit Spectroscopic Explorer(MUSE) on the Very Large Telescope (VLT) to identify and characterizebona fide multiple image families and measure their redshifts down tom_F814W ≃ 26. A total of 16 background sources over theredshift range 1.0-6.1 are multiply lensed into 47 images 24 of whichare spectroscopically confirmed and belong to ten individual sources.These also include a multiply lensed Lyman-α blob at z = 3.118.The cluster total mass distribution and underlying cosmology in themodels are optimized by matching the observed positions of the multipleimages on the lens plane. Bayesian Markov chain Monte Carlo techniquesare used to quantify errors and covariances of the best-fit parameters. Results: We show that with a careful selection of a large sampleof spectroscopically confirmed multiple images the best-fit model canreproduce their observed positions with a rms scatter of 0.̋3 in afixed flat ΛCDM cosmology whereas the lack of spectroscopicinformation or the use of inaccurate photometric redshifts can lead tobiases in the values of the model parameters. We find that the best-fitparametrization for the cluster total mass distribution is composed ofan elliptical pseudo-isothermal mass distribution with a significantcore for the overall cluster halo and truncated pseudo-isothermal massprofiles for the cluster galaxies. We show that by adding bona fidephotometric-selected multiple images to the sample of spectroscopicfamilies one can slightly improve constraints on the model parameters.In particular we find that the degeneracy between the lens total massdistribution and the underlying geometry of the Universe which isprobed via angular diameter distance ratios between the lens and sourcesand the observer and sources can be partially removed. Allowingcosmological parameters to vary together with the cluster parameters wefind (at 68% confidence level) Ω_m = 0.25^+0.13_-0.16 and w = -1.07^+0.16_-0.42 for a flat ΛCDM model andΩ_m = 0.31^+ 0.12_-0.13 andΩ_Λ = 0.38^+ 0.38_-0.27 for aUniverse with w = -1 and free curvature. Finally using toy modelsmimicking the overall configuration of multiple images and cluster totalmass distribution we estimate the impact of the line-of-sight massstructure on the positional rms to be 0.̋3 ± 0. We arguethat the apparent sensitivity of our lensing model to cosmography is dueto the combination of the regular potential shape of RXC J2248 a largenumber of bona fide multiple images out to z = 6.1 and a relativelymodest presence of intervening large-scale structure as revealed by ourspectroscopic survey.
CLASH-VLT: A highly precise strong lensing model of the galaxy cluster RXC J2248.7-4431 (Abell S1063) and prospects for cosmography
Mercurio A;
2016-01-01
Abstract
Aims: We perform a comprehensive study of the total massdistribution of the galaxy cluster RXC J2248.7-4431 (z = 0.348) with aset of high-precision strong lensing models which take advantage ofextensive spectroscopic information on many multiply lensed systems. Inthe effort to understand and quantify inherent systematics in parametricstrong lensing modelling we explore a collection of 22 models in whichwe use different samples of multiple image families differentparametrizations of the mass distribution and cosmological parameters. Methods: As input information for the strong lensing models weuse the Cluster Lensing And Supernova survey with Hubble (CLASH) imagingdata and spectroscopic follow-up observations with the VIsibleMulti-Object Spectrograph (VIMOS) and Multi Unit Spectroscopic Explorer(MUSE) on the Very Large Telescope (VLT) to identify and characterizebona fide multiple image families and measure their redshifts down tom_F814W ≃ 26. A total of 16 background sources over theredshift range 1.0-6.1 are multiply lensed into 47 images 24 of whichare spectroscopically confirmed and belong to ten individual sources.These also include a multiply lensed Lyman-α blob at z = 3.118.The cluster total mass distribution and underlying cosmology in themodels are optimized by matching the observed positions of the multipleimages on the lens plane. Bayesian Markov chain Monte Carlo techniquesare used to quantify errors and covariances of the best-fit parameters. Results: We show that with a careful selection of a large sampleof spectroscopically confirmed multiple images the best-fit model canreproduce their observed positions with a rms scatter of 0.̋3 in afixed flat ΛCDM cosmology whereas the lack of spectroscopicinformation or the use of inaccurate photometric redshifts can lead tobiases in the values of the model parameters. We find that the best-fitparametrization for the cluster total mass distribution is composed ofan elliptical pseudo-isothermal mass distribution with a significantcore for the overall cluster halo and truncated pseudo-isothermal massprofiles for the cluster galaxies. We show that by adding bona fidephotometric-selected multiple images to the sample of spectroscopicfamilies one can slightly improve constraints on the model parameters.In particular we find that the degeneracy between the lens total massdistribution and the underlying geometry of the Universe which isprobed via angular diameter distance ratios between the lens and sourcesand the observer and sources can be partially removed. Allowingcosmological parameters to vary together with the cluster parameters wefind (at 68% confidence level) Ω_m = 0.25^+0.13_-0.16 and w = -1.07^+0.16_-0.42 for a flat ΛCDM model andΩ_m = 0.31^+ 0.12_-0.13 andΩ_Λ = 0.38^+ 0.38_-0.27 for aUniverse with w = -1 and free curvature. Finally using toy modelsmimicking the overall configuration of multiple images and cluster totalmass distribution we estimate the impact of the line-of-sight massstructure on the positional rms to be 0.̋3 ± 0. We arguethat the apparent sensitivity of our lensing model to cosmography is dueto the combination of the regular potential shape of RXC J2248 a largenumber of bona fide multiple images out to z = 6.1 and a relativelymodest presence of intervening large-scale structure as revealed by ourspectroscopic survey.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
