CLASH-VLT: Insights on the mass substructures in the Frontier Fields Cluster MACS J0416.1-2403 through accurate strong lens modeling (1407.7866v2)

Abstract: We present a detailed mass reconstruction and a novel study on the substructure properties in the core of the CLASH and Frontier Fields galaxy cluster MACS J0416.1-2403. We show and employ our extensive spectroscopic data set taken with the VIMOS instrument as part of our CLASH-VLT program, to confirm spectroscopically 10 strong lensing systems and to select a sample of 175 plausible cluster members to a limiting stellar mass of log(M_*/M_Sun) ~ 8.6. We reproduce the measured positions of 30 multiple images with a remarkable median offset of only 0.3" by means of a comprehensive strong lensing model comprised of 2 cluster dark-matter halos, represented by cored elliptical pseudo-isothermal mass distributions, and the cluster member components. The latter have total mass-to-light ratios increasing with the galaxy HST/WFC3 near-IR (F160W) luminosities. The measurement of the total enclosed mass within the Einstein radius is accurate to ~5%, including systematic uncertainties. We emphasize that the use of multiple-image systems with spectroscopic redshifts and knowledge of cluster membership based on extensive spectroscopic information is key to constructing robust high-resolution mass maps. We also produce magnification maps over the central area that is covered with HST observations. We investigate the galaxy contribution, both in terms of total and stellar mass, to the total mass budget of the cluster. When compared with the outcomes of cosmological $N$-body simulations, our results point to a lack of massive subhalos in the inner regions of simulated clusters with total masses similar to that of MACS J0416.1-2403. Our findings of the location and shape of the cluster dark-matter halo density profiles and on the cluster substructures provide intriguing tests of the assumed collisionless, cold nature of dark matter and of the role played by baryons in the process of structure formation.

Strong Lensing Analysis in Galaxy Cluster MACS J0416.1-2403

The paper "CLASH-VLT: Insights on the mass substructures in MACS J0416.1$-$2403 through accurate strong lens modeling" presents a comprehensive strong lensing analysis of the galaxy cluster MACS J0416.1$-$2403. Utilizing observations from the Hubble Space Telescope (HST) and spectroscopic data from the VIsible Multi-Object Spectrograph (VIMOS) at the Very Large Telescope (VLT), the paper aims to derive precise mass reconstructions and explore substructure properties in this cluster. This analysis forms part of the Cluster Lensing And Supernova survey with Hubble (CLASH) and Frontier Fields initiatives.

The authors employ a robust dataset of spectroscopically confirmed multiple-image systems and cluster member galaxies, fostering high-resolution mass models. The selected approach focuses on 10 spectroscopically confirmed strong lensing systems, yielding 30 multiple images. They achieve a remarkably accurate median offset of only 0.3" between observed and predicted image positions using a sophisticated strong lensing model, incorporating 2 cluster dark-matter halos and numerous cluster member components. The main results are derived from a mass model consisting of pseudo-isothermal elliptical mass distributions, revealing nuanced insights into the total and luminous mass distributions of the cluster.

Examining the implications of the findings, the paper highlights a significant absence of massive subhalos in inner regions when contrasted with cosmological $N$-body simulations, providing a critical test of cold dark matter and the influence of baryonic physics in structure formation. The work underscores the paramount importance of spectroscopically robust data in enhancing the accuracy of mass models.

Quantitatively, the enclosed mass within the Einstein radius is constrained within ~5% precision, factoring in uncertainties across six distinct models. The mass profiles exhibit relatively flat inner density distributions, diverging notably from previously established models, indicating potential departures in underlying assumptions or environmental factors affecting subhalos.

Practical implications of this paper are multifaceted, encompassing both observational and theoretical domains. Observationally, it underscores the capacity for ground-based telescopic data to refine space-borne observations, thereby enhancing the scientific returns on flagship programs like the HFF. Theoretically, these results contribute to understanding the complex interplay between dark matter and baryonic matter in cluster cores and the evolution of substructure properties under cosmic expansion and hierarchical assembly models. This work lays a foundation for future research exploring the distribution and evolution of baryons in galactic environments, probing deeper into the nature of dark matter and the gravitational framework it forms across cosmic scales.

The paper also invites future development in lensing analysis methodologies, suggesting pathways for integrating complementary data, including weak lensing and X-ray observations. It highlights the need for synergistic investigations incorporating simulation frameworks to draw more precise correlations between observed cluster properties and theoretical predictions. Overall, this work plays a vital role in advancing the cosmological narrative, offering a nuanced glimpse into the dynamical underpinnings of massive galaxy clusters and their constituent substructures.