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Register a new userHubble Frontier Fields : A High Precision Strong Lensing Analysis of Galaxy Cluster MACSJ0416.1-2403 using ~200 Multiple Images
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Mathilde Jauzac
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We present a high-precision mass model of the galaxy cluster MACSJ0416.1-2403, based on a strong-gravitational-lensing analysis of the recently acquired Hubble Space Telescope Frontier Fields (HFF) imaging data. Taking advantage of the unprecedented depth provided by HST/ACS observations in three passbands, we identify 51 new multiply imaged galaxies, quadrupling the previous census and bringing the grand total to 68, comprising 194 individual lensed images. Having selected a subset of the 57 most securely identified multiply imaged galaxies, we use the Lenstool software package to constrain a lens model comprised of two cluster-scale dark-matter halos and 98 galaxy-scale halos. Our best-fit model predicts image positions with an $RMS$ error of 0.68, which constitutes an improvement of almost a factor of two over previous, pre-HFF models of this cluster. We find the total projected mass inside a 200~kpc aperture to be $(1.60pm0.01)times 10^{14} M_odot$, a measurement that offers a three-fold improvement in precision, reaching the percent level for the first time in any cluster. Finally, we quantify the increase in precision of the derived gravitational magnification of high-redshift galaxies and find an improvement by a factor of $sim$2.5 in the statistical uncertainty. Our findings impressively confirm that HFF imaging has indeed opened the domain of high-precision mass measurements for massive clusters of galaxies.
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We present a high-precision mass model of galaxy cluster Abell 2744, based on a strong-gravitational-lensing analysis of the emph{Hubble Space Telescope Frontier Fields} (HFF) imaging data, which now include both emph{Advanced Camera for Surveys} and emph{Wide-Field Camera 3} observations to the final depth. Taking advantage of the unprecedented depth of the visible and near-infrared data, we identify 34 new multiply imaged galaxies, bringing the total to 61, comprising 181 individual lensed images. In the process, we correct previous erroneous identifications and positions of multiple systems in the northern part of the cluster core. With the textsc{Lenstool} software and the new sets of multiple images, we model the cluster using two cluster-scale dark matter halos plus galaxy-scale halos for the cluster members. Our best-fit model predicts image positions with an emph{RMS} error of 0.69$arcsec$, which constitutes an improvement by almost a factor of two over previous parametric models of this cluster. We measure the total projected mass inside a 200~kpc aperture as ($2.162pm 0.005$)$times 10^{14}M_{odot}$, thus reaching 1% level precision for the second time, following the recent HFF measurement of MACSJ0416.1-2403. Importantly, the higher quality of the mass model translates into an overall improvement by a factor of 4 of the derived magnification factor. % for the high-redshift lensed background galaxies. Together with our previous HFF gravitational lensing analysis, this work demonstrates that the HFF data enables high-precision mass measurements for massive galaxy clusters and the derivation of robust magnification maps to probe the early Universe.
We use a joint optical/X-ray analysis to constrain the geometry and history of the ongoing merging event in the massive galaxy cluster MACSJ0416.1-2403 (z=0.397). Our investigation of cluster substructure rests primarily on a combined strong- and weak-lensing mass reconstruction based on the deep, high-resolution images obtained for the Hubble Frontier Fields initiative. To reveal the systems dynamics, we complement this lensing analysis with a study of the intra-cluster gas using shallow Chandra data, and a three-dimensional model of the distribution and motions of cluster galaxies derived from over 100 spectroscopic redshifts. The multi-scale grid model obtained from our combined lensing analysis extends the high-precision strong-lensing mass reconstruction recently performed to cluster-centric distances of almost 1 Mpc. Our analysis detects the two well known mass concentrations in the cluster core. A pronounced offset between collisional and collisionless matter is only observed for the SW cluster component, while excellent alignment is found for the NE cluster. Both the lensing analysis and the distribution of cluster light strongly suggest the presence of a third massive structure, almost 2 arcmin SW of the cluster centre. Since no X-ray emission is detected in this region, we conclude that this structure is non-virialised and speculate that it might be part of a large-scale filament almost aligned with our line of sight. Combining all evidence from the distribution of dark and luminous matter, we propose two alternative scenarios for the trajectories of the components of MACSJ0416.1-2403. Upcoming deep X-ray observations that allow the detection of shock fronts, cold cores, and sloshing gas (all key diagnostics for studies of cluster collisions) will allow us to test, and distinguish between these two scenarios.
We present a new high-precision parametric strong lensing model of the galaxy cluster MACS J0416.1-2403, at z=0.396, which takes advantage of the MUSE Deep Lensed Field (MDLF), with 17.1h integration in the northeast region of the cluster, and Hubble Frontier Fields data. We spectroscopically identify 182 multiple images from 48 background sources at 0.9<z<6.2, and 171 cluster member galaxies. Several multiple images are associated to individual clumps in multiply lensed resolved sources. By defining a new metric, which is sensitive to the gradients of the deflection field, we show that we can accurately reproduce the positions of these star-forming knots despite their vicinity to the model critical lines. The high signal-to-noise ratio of the MDLF spectra enables the measurement of the internal velocity dispersion of 64 cluster galaxies, down to m(F160W)=22. This allowed us to independently estimate the contribution of the subhalo mass component of the lens model from the measured Faber-Jackson scaling relation. Our best reference model, which represents a significant step forward compared to our previous analyses, was selected from a comparative study of different mass parametrizations. The root-mean-square displacement between the observed and model-predicted image positions is only 0.40, which is 33% smaller than in all previous models. The mass model appears to be particularly well constrained in the MDLF region. We characterize the robustness of the magnification map at varying distances from the model critical lines and the total projected mass profile of the cluster.
We present an analysis of MUSE observations obtained on the massive Frontier Fields cluster Abell 2744. This new dataset covers the entire multiply-imaged region around the cluster core. We measure spectroscopic redshifts for HST-selected continuum sources together with line emitters blindly detected in the datacube. The combined catalog consists of 514 spectroscopic redshifts (with 414 new identifications), including 156 cluster members and 326 magnified background sources. We use this redshift information to perform a strong-lensing analysis of all multiple images previously found in the deep Frontier Field images, and add three new MUSE-detected multiply-imaged systems with no obvious HST counterpart. The combined strong lensing constraints include a total of 60 systems producing 188 images altogether, out of which 29 systems and 83 images are spectroscopically confirmed, making Abell 2744 one of the most well-constrained clusters to date. A parametric mass model including two cluster-scale components in the core and several group-scale substructures at larger radii accurately reproduces all the spectroscopic multiple systems, reaching an rms of 0.67 in the image plane. Overall, the large number of spectroscopic redshifts gives us a robust model and we estimate the systematics on the mass density and magnification within the cluster core to be typically ~9%.
We present VIMOS-VLT spectroscopy of the Frontier Fields cluster MACS~J0416.1-2403 (z=0.397). Taken as part of the CLASH-VLT survey, the large spectroscopic campaign provided more than 4000 reliable redshifts, including ~800 cluster member galaxies. The unprecedented sample of cluster members at this redshift allows us to perform a highly detailed dynamical and structural analysis of the cluster out to ~2.2$r_{200}$ (~4Mpc). Our analysis of substructures reveals a complex system composed of a main massive cluster ($M_{200}$~0.9$times 10^{15} M_{odot}$) presenting two major features: i) a bimodal velocity distribution, showing two central peaks separated by $Delta V_{rf}$~1100 km s$^{-1}$ with comparable galaxy content and velocity dispersion, ii) a projected elongation of the main substructures along the NE-SW direction, with a prominent subclump ~600 kpc SW of the center and an isolated BCG approximately halfway between the center and the SW clump. We also detect a low mass structure at z~0.390, ~10 S of the cluster center, projected at ~3Mpc, with a relative line-of-sight velocity of $Delta V_{rf}$~-1700 km s$^{-1}$. The cluster mass profile that we obtain through our dynamical analysis deviates significantly from the universal NFW, being best fit by a Softened Isothermal Sphere model instead. The mass profile measured from the galaxy dynamics is found to be in relatively good agreement with those obtained from strong and weak lensing, as well as with that from the X-rays, despite the clearly unrelaxed nature of the cluster. Our results reveal overall a complex dynamical state of this massive cluster and support the hypothesis that the two main subclusters are being observed in a pre-collisional phase, in line with recent findings from radio and deep X-ray data. With this article we also release the entire redshift catalog of 4386 sources in the field of this cluster.
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