Inside a Beehive: The Multiple Merging Processes in the Galaxy Cluster Abell 2142^*

Abstract

To investigate the dynamics of the galaxy cluster A2142, we compile an extended catalog of 2239 spectroscopic redshifts of sources, including newly measured 237 redshifts, within 30 arcmin from the cluster center. With the σ-plateau algorithm from the caustic method, we identify 868 members and a number of substructures in the galaxy distribution both in the outskirts, out to ∼3.5 Mpc from the cluster center, and in the central region. In the outskirts, one substructure overlaps a falling clump of gas previously identified in the X-ray band. These substructures suggests the presence of multiple minor mergers, which are responsible for the complex dynamics of A2142, and the absence of recent or ongoing major mergers. We show that the distribution of the galaxies in the cluster core and in several substructures are consistent with the mass distribution inferred from the weak lensing signal. Moreover, we use spatially-resolved X-ray spectroscopy to measure the redshift of different regions of the intracluster medium within ∼3 arcmin from the cluster center. We find a ring of gas near the two X-ray cold fronts identified in previous analyses and measure a velocity of this ring of 810 ± 330kms −1 larger than the cluster mean velocity. Our analysis suggests the presence of another ring surrounding the core, whose velocity is 660 ± 300kms −1 larger than the cluster velocity. These X-ray features are not associated to any optical substructures, and support the core-sloshing scenario suggested in previous work. a a We dedicate this paper to the late Bepi Tormen, our beloved friend and colleague whose enthusiastic and intense work on gravitational dynamics largely contributed to our current understanding of the formation and evolution of galaxy clusters.

Multiscale cosmic web detachments, connectivity, and preprocessing in the supercluster SCl A2142 cocoon

“…The infall zone extends approximately up to 2 h −1 Mpc from the cluster centre. This agrees with the clustercentric distance limit for the cluster members in the caustic diagram by Liu et al (2018). In this region, the stellar ages and star-formation rates of galaxies change rapidly (Einasto et al 2018b).…”

Cluster–galaxy weak lensing

“…For both clusters, the observed hg þ ð#Þi profiles are better fitted by the NFW model having an outward-steepening density profile. Abell 2142 is a nearby cluster at z l ¼ 0:091 perturbed by merging substructures (e.g., Okabe and Umetsu 2008;Umetsu et al 2009;Liu et al 2018). The radial curvature observed in the hg þ i profile of Abell 2142 is highly pronounced, so that the power-law SIS model is strongly disfavored by the Subaru weak-lensing data.…”

“…The radial curvature observed in the hg þ i profile of Abell 2142 is highly pronounced, so that the power-law SIS model is strongly disfavored by the Subaru weak-lensing data. From the best-fit NFW model, the mass and concentration parameters of Abell 2142 are constrained as M 200c ¼ ð9:1 AE 1:9Þ Â 10 14 h À1 M and c 200c ¼ 4:1 AE 0:8 (Umetsu et al 2009;Liu et al 2018).…”

Line-of-Sight Gas Sloshing in the Cool Core of Abell 907

“…For example, in the case of Abell 1835, the upper limit of redshift offset corresponds to ∆v < 600 km s −1 (Ueda et al 2017). Liu et al (2018) measured the redshift offset of the cold fronts relative to the cluster average in Abell 2142 to be 810 ± 330 km s −1 . For the Perseus cluster, Hitomi Collaboration et al (2018) reported the velocity gradient with a 100 km s −1 amplitude across the cluster core, which is likely associated with a sloshing motion in the plane of the sky.…”