Pilot-WINGS: An extended MUSE view of the structure of Abell 370

TL;DR

This study uses wide-field MUSE IFU spectroscopy combined with HST imaging to analyze the structure, mass distribution, and galaxy properties of the galaxy cluster Abell 370 beyond its core, revealing new insights into its outskirts.

Contribution

It provides the first detailed analysis of Abell 370's outskirts using extended MUSE IFU data, including mass profiling and identification of galaxy-galaxy lenses outside the Einstein radius.

Findings

Extended MUSE mosaic covers beyond the Einstein radius.

Identified 416 cluster galaxies and their kinematics.

Detected multiple external overdensities affecting mass estimates.

Abstract

We investigate the strong-lensing cluster Abell 370 (A370) using a wide Integral Field Unit (IFU) spectroscopic mosaic from the Multi-Unit Spectroscopic Explorer (MUSE). IFU spectroscopy provides significant insight into the structure and mass content of galaxy clusters, yet IFU-based cluster studies focus almost exclusively on the central Einstein-radius region. Covering over 14 arcmin$^2$, the new MUSE mosaic extends significantly beyond the A370 Einstein radius, providing, for the first time, a detailed look at the cluster outskirts. Combining these data with wide-field, multi-band Hubble Space Telescope (HST) imaging from the BUFFALO project, we analyse the distribution of objects within the cluster and along the line of sight. Identifying 416 cluster galaxies, we use kinematics to trace the radial mass profile of the halo, providing a mass estimate independent from the lens model. We also measure radially-averaged properties of the cluster members, tracking their evolution as a function of infall. Thanks to the high spatial resolution of our data, we identify six cluster members acting as galaxy-galaxy lenses, which constrain localized mass distributions beyond the Einstein radius. Finally, taking advantage of MUSE's 3D capabilities, we detect and analyse multiple spatially extended overdensities outside of the cluster that influence lensing-derived halo mass estimates. We stress that much of this work is only possible thanks to the robust, extended IFU coverage, highlighting its importance even in less optically dense cluster regions. Overall, this work showcases the power of combining HST+MUSE, and serves as the initial step towards a larger and wider program targeting several clusters.