Setting the scene for BUFFALO: A study of the matter distribution in the HFF galaxy cluster MACS J0416.1-2403 and its parallel field

In the context of the Beyond Ultradeep Frontier Fields And Legacy Observations (BUFFALO) survey, we present a new analysis of the merging galaxy cluster MACS J0416.1−2403 (z = 0.397) and its parallel field using Hubble Frontier Fields (HFF) data. We measure the surface mass density from a weak-lensing analysis and characterize the overall matter distribution in both the cluster and parallel fields. The surface mass distribution derived for the parallel field shows clumpy overdensities connected by filament-like structures elongated in the direction of the cluster core. We also characterize the X-ray emission in the parallel field and compare it with the lensing mass distribution. We identify five mass peaks at the >5σ level over the two fields, four of them being in the cluster one. Three of them are located close to galaxy overdensities and one is also close to an excess in the X-ray emission. Nevertheless, two of them have neither optical nor X-ray counterpart and are located close to the edges of the field of view, thus further studies are needed to confirm them as substructures. Finally, we compare our results with the predicted subhalo distribution of one of the Hydrangea/C-EAGLE simulated cluster. Significant differences are obtained suggesting the simulated cluster is at a more advanced evolutionary stage than MACS J0416.1−2403. Our results anticipate the upcoming BUFFALO observations that will link the two HFF fields, extending further the HST coverage.