2020MNRAS.495.2007M

The galaxy cluster Abell 1644 ({bar}z=0.047) is known for its remarkable spiral-like X-ray emission. It was previously identified as a bimodal system, comprising the subclusters, A1644S and A1644N, each one centred on a giant elliptical galaxy. In this work, we present a comprehensive study of this system, including new weak lensing and dynamical data and analysis plus a tailor-made hydrodynamical simulation. The lensing and galaxy density maps showed a structure in the North that could not be seen on the X-ray images. We, therefore, rename the previously known northern halo as A1644N1 and the new one as A1644N2. Our lensing data suggest that those have fairly similar masses: M₂₀₀^N1=0.90_–0.85^+0.45 ×10¹⁴ and M₂₀₀^N2=0.76_–0.75^+0.37 ×10¹⁴ M_☉, whereas the southern structure is the main one: M₂₀₀^S=1.90_–1.28^+0.89×10¹⁴ M_☉. Based on the simulations, fed by the observational data, we propose a scenario where the remarkable X-ray characteristics in the system are the result of a collision between A1644S and A1644N2 that happened ∼1.6 Gyr ago. Currently, those systems should be heading to a new encounter, after reaching their maximum separation.