Oral Presentation
Deciphering a Galaxy Cluster Merger with Extreme Relic Separation: A Weak-Lensing Study of PSZ2 G181.06+48.47
Presenter: Eunmo Ahn (Yonsei University)
Galaxy cluster mergers rank among the most energetic and transformative events in the Universe, offering critical insights into large-scale structure evolution and the nature of dark matter. The galaxy cluster PSZ2 G181.06+48.47 (PSZ2G181) serves as a compelling case study with an unusually large double radio relic separation of ~2.7 Mpc – a striking outlier given its relatively low mass (M_500 ~ 3x10^14 solar masses). We present a weak gravitational lensing (WL) analysis of PSZ2G181 using Subaru/Hyper Suprime-Cam, revealing a bimodal mass distribution with subclusters separated by ~500 kpc and a 3:1 mass ratio. Our mass maps reveal that the relics are located near the cluster’s virial radius, where the intracluster medium (ICM) density is extremely low–highlighting PSZ2G181 as a unique testbed for understanding plasma acceleration in tenuous environments. By combining WL-derived mass estimates with both idealized and cosmological simulations, we explored a range of merger scenarios. Our results favor a returning phase ~0.9 Gyr after the first collision, where the two subclusters are heading for a second collision after reaching their first apocenter. Other possibilities, including an outgoing scenario after the second collision or a configuration with a large viewing angle projection, are also considered. The integration of multi-wavelength data, WL analysis, and numerical simulations enables a detailed reconstruction of the merger history, offering new insights into dark matter dynamics and the role of mergers in shaping large-scale structure.
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