Revising the merger scenario of the galaxy cluster Abell 1644: a new gas poor structure discovered by weak gravitational lensing

Abstract

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 centered 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 suggests that those have fairly similar masses: $M_{200}^{N1}=0.90_{-0.85}^{+0.45}\times 10^{14}$ and $M_{200}^{N2}=0.76_{-0.75}^{+0.37}\times 10^{14}$ M${}_{\odot }$, whereas the southern structure is the main one: $M_{200}^{\mathrm{S}}=1.90_{-1.28}^{+0.89}\times 10^{14}$ M${}_{\odot }$. 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 $\sim$1.6 Gyr ago. Currently, those systems should be heading to a new encounter, after reaching their maximum separation.

16 pages, 11 figures, 8 tables. Accepted for publication in MNRAS in 2020 April 27