A free-form lensing model of A370 revealing stellar mass dominated BCGs, in Hubble Frontier Fields images

TL;DR

This study constructs a detailed free-form gravitational lensing model of galaxy cluster A370, revealing that the stellar mass of its Brightest Cluster Galaxies predominantly accounts for their lensing profiles, with limited dark matter influence within 100 kpc.

Contribution

It presents a novel free-form lens model of A370 that accurately constrains BCG mass profiles using radially lensed images, highlighting stellar mass dominance.

Findings

BCGs' lensing profiles are mainly due to stellar mass.

Dark matter contributes modestly within 100 kpc of BCGs.

Model consistency confirmed across independent subsamples.

Abstract

We derive a free-form mass distribution for the unrelaxed cluster A370 (z=0.375), using the latest Hubble Frontier Fields images and GLASS spectroscopy. Starting from a reliable set of 10 multiply lensed systems we produce a free-form lens model that identifies ~ 80 multiple-images. Good consistency is found between models using independent subsamples of these lensed systems, with detailed agreement for the well resolved arcs. The mass distribution has two very similar concentrations centred on the two prominent Brightest Cluster Galaxies (or BCGs), with mass profiles that are accurately constrained by a uniquely useful system of long radially lensed images centred on both BCGs. We show that the lensing mass profiles of these BCGs are mainly accounted for by their stellar mass profiles, with a modest contribution from dark matter within r<100 kpc of each BCG. This conclusion may favour a cooled cluster gas origin for BCGs, rather than via mergers of normal galaxies for which dark matter should dominate over stars. Growth via merging between BCGs is, however, consistent with this finding, so that stars still dominate over dark matter .