Minor Merger-Induced Cold Fronts in Abell 2142 and RXJ1720.1+2638

Abstract

We present evidence for the existence of substructure in the "relaxed appearing" cold front clusters Abell 2142 and RXJ1720.1+2638. The detection of these substructures was made possible by comprehensive multi-object optical spectroscopy obtained with the Hectospec and DEep Imaging Multi-Object Spectrograph instruments on the 6.5 m MMT and 10 m Keck II telescope, respectively. These observations produced 956 and 400 spectroscopically confirmed cluster members within a projected radius of 3 Mpc from the centers of A2142 and RXJ1720.1+2638, respectively. The substructure manifests itself as local peaks in the spatial distribution of member galaxies and also as regions of localized velocity substructure. For both Abell 2142 and RXJ1720.1+2638, we identify group-scale substructures which, when considering the morphology of the cold fronts and the time since pericentric passage of a perturber estimated from the cold front radii, could plausibly have perturbed the cluster cores and generated the cold fronts observed in Chandra images. The results presented here are consistent with cold fronts being the result of merger activity and with cold fronts in relaxed appearing clusters being due to minor merger activity.

Mass, velocity anisotropy, and pseudo phase-space density profiles of Abell 2142

“…In fact, the X-ray emission appears to have an elliptical morphology elongated in the north-west south-east direction (Markevitch et al 2000;Akamatsu et al 2011). The merging scenario is also supported by the presence of substructures of galaxies lying along the direction of the cluster elongation, as found in the SZ maps by Umetsu et al (2009), lensing analysis by Okabe & Umetsu (2008), and analysis of the distribution of LOS velocities of Owers et al (2011). However, after analysing XMMNewton images to investigate the cold fronts of A2142, Rossetti et al (2013) argue that the mergers have intermediate mass ratios rather than major ones.…”

“…Could these lower mass concentrations found by methods based upon internal kinematics be a sign that A2142 is out of dynamical equilibrium? The substructures found by Owers et al (2011) and the results by Rossetti et al (2013) on the importance of the mergers undergone by A2142 suggest that full relaxation is to be excluded. On the other hand, the agreement on the virial radius amongst the different methods and with the results from X-ray and lensing (the latter does not require equilibrium) suggests that A2142 is not far from dynamical equilibrium.…”

“…The spectroscopic information has been provided by Owers et al (2011). The full sample is composed of 1631 galaxies with both photometric and spectroscopic information.…”

“…Coordinates with respect to the cluster center, radii, and number of galaxies of the three main substructures, as found by Owers et al (2011). following the nomenclature of Owers et al (2011). Therefore, we remove galaxies inside circles, the centres and radii of which are reported in Table 1.…”

Abell 2142 at large scales: An extreme case for sloshing?

“…When the sloshing mechanism was suggested to explain the presence of cold fronts in relaxed clusters, the striking similarity of the edges in the Chandra image of A2142 with the concentric arcs seen in simulation led to the change of the interpretation of cold fronts in this cluster as being caused by the sloshing of the core (Tittley & Henriksen 2005;Markevitch & Vikhlinin 2007). Recently, Owers et al (2011) studied the galaxy distributions in A2142 and, comparing it to the X-ray morphology, identified two candidate perturbers that could have induced the sloshing of the core and that move mainly along the line of sight. In this scenario, the typical sloshing spiral that is coplanar with the perturber orbit is seen edge on, creating the concentric arc features observed in the Chandra maps.…”