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

Abstract

We present line-of-sight gas sloshing first found in a cool core in a galaxy cluster. The galaxy cluster Abell 907 is identified as a relaxed cluster owing to its global X-ray surface brightness taken by the Chandra X-ray Observatory. The X-ray residual image after removing the global emission of the intracluster medium (ICM), however, shows an arc-like positive excess and a negative excess surrounding the central positive excess in the cluster core, which in turn indicates a disturbance of the ICM. We analyze the X-ray spectra extracted from both regions and find that (1) the ICM temperature and the metal abundance in the positive excess are lower and higher than those in the negative excess, respectively, and (2) the ICM is nearly in pressure equilibrium. We also find a slight redshift difference between the positive and the negative excesses, which corresponds to the velocity shear of 1680 +1300 −920 km s −1 (1σ). The X-ray residual image and the ICM properties are consistent with those expected by line-of-sight gas sloshing. Assuming that the gas is moving toward inverse-parallel to each other along the line-of-sight, the shear velocity is expected to be ∼ 800 km s −1 . The velocity field of this level is able to provide non-thermal pressure support by ∼ 34% relative to the thermal one. The total kinetic energy inferred from the shear velocity corresponds to ∼ 30 % of the bolometric luminosity of the sloshing ICM. Abell 907 is therefore complementary to galaxy clusters in which gas sloshing takes place in the plane of the sky, and is important for understanding gas dynamics driven by sloshing and its influence on the heating to prevent runaway cooling.

Gas Density Perturbations in the Cool Cores of CLASH Galaxy Clusters

“…This cluster seems to experience line-of-sight gas sloshing. The pattern in the X-ray residual image is similar to that found in Abell 907, which is identified as the system of line-of-sight sloshing (Ueda et al 2019). In addition, the best-fit parameters of the ICM properties in both the positive and negative excess regions are consistent with those expected by line-of-sight gas sloshing.…”

“…Bulk motion in a cool core, generated by gas sloshing, was recently found (Hitomi Collaboration et al 2018;Ueda et al 2019) and its kinetic energy is considered to be converted into heat by dissipating turbulence produced by e.g., the Kelvin-Helmholtz instability (KHI; e.g., ZuHone et al 2010;Roediger et al 2012;ZuHone & Roediger 2016). Evidence of gas sloshing is frequently found in cool cores (e.g., Churazov et al 2003;Clarke et al 2004;Blanton et al 2011;Owers et al 2011;O'Sullivan et al 2012;Canning et al 2013;Rossetti et al 2013;Ghizzardi et al 2014;Sanders et al 2014;Ichinohe et al 2015;Ueda et al 2017;Su et al 2017;Liu et al 2018;Ueda et al 2018;Calzadilla et al 2019;Ueda et al 2019). The wellknown characteristic features of gas sloshing are that (1) the ICM in the cool core exhibits a characteristic pair of positive and negative density perturbations in the X-ray brightness distribution, (2) the temperature (abundance) of the ICM in the positive excess region is lower (higher) than that in the negative excess area, and (3) the ICM in both regions is in pressure equilibrium.…”

“…Gas sloshing is induced by (minor) mergers with a nonzero impact parameter (see Markevitch & Vikhlinin 2007, for a review). Bulk motion in a cool core, generated by gas sloshing, was recently found (Hitomi Collaboration et al 2018;Ueda et al 2019) and its kinetic energy is considered to be converted into heat by dissipating turbulence produced by e.g., the Kelvin-Helmholtz instability (KHI; e.g., ZuHone et al 2010;Roediger et al 2012;ZuHone & Roediger 2016). Evidence of gas sloshing is frequently found in cool cores (e.g., Churazov et al 2003;Clarke et al 2004;Blanton et al 2011;Owers et al 2011;O'Sullivan et al 2012;Canning et al 2013;Rossetti et al 2013;Ghizzardi et al 2014;Sanders et al 2014;Ichinohe et al 2015;Ueda et al 2017;Su et al 2017;Liu et al 2018;Ueda et al 2018;Calzadilla et al 2019;Ueda et al 2019).…”

Multiwavelength view of SPT-CL J2106-5844. The radio galaxies and the thermal and relativistic plasmas in a massive galaxy cluster merger at z~1.13

“…Since the sloshing motion happens in the subsonic/transonic regime (e.g. Ueda et al 2018Ueda et al , 2019, the SZ effect should remain relatively unperturbed. For sloshing taking place in the plane of sky, the measured X-ray surface brightness would be dominated by the emission from the colder and denser gas,which does not necessarily coincide with the peak of the line-of-sight-integrated electron pressure.…”

The Dynamical State of the Frontier Fields Galaxy Cluster Abell 370

“…We followed standard data reduction and cleaning procedures using the updated versions 4.9 of Chandra Interactive Analysis of Observations (CIAO; Fruscione et al 2006) and version 4.7.8 of the calibration database (CALDB; for details of our procedure see Ueda et al 2019). After cleaning the data, the remaining exposure time was 70 ksec.…”