Gas Sloshing Regulates and Records the Evolution of the Fornax Cluster

Abstract

We present results of a joint Chandra and XMM-Newton analysis of the Fornax Cluster, the nearest galaxy cluster in the southern sky. Signatures of merger-induced gas sloshing can be seen in the X-ray image. We identify four sloshing cold fronts in the intracluster medium, residing at radii of 3 kpc (west), 10 kpc (northeast), 30 kpc (southwest), and 200 kpc (east). Despite spanning over two orders of magnitude in radius, all four cold fronts fall onto the same spiral pattern that wraps around the BCG NGC. 1399, likely all initiated by the infall of NGC. 1404. The most evident front is to the northeast, 10 kpc from the cluster center, which separates low-entropy high-metallicity gas and high-entropy low-metallicity gas. The metallicity map suggests that gas sloshing, rather than an AGN outburst, is the driving force behind the redistribution of the enriched gas in this cluster. The innermost cold front resides within the radius of the strong cool core. The sloshing timescale within the cooling radius, calculated from the Brunt-Vasala frequency, is an order of magnitude shorter than the cooling time. It is plausible that gas sloshing is contributing to the heating of the cool core, provided that gas of different entropies can be mixed effectively via Kelvin-Helmholtz instability. The estimated age of the outermost front suggests that this is not the first infall of NGC. 1404.

Description
Keywords
galaxies: clusters: intracluster medium, X-rays: galaxies: clusters, KELVIN-HELMHOLTZ INSTABILITIES, XMM-NEWTON OBSERVATIONS, INTRACLUSTER MEDIUM, COOLING FLOWS, COLD FRONTS, METALLICITY GRADIENTS, SURFACE BRIGHTNESS, MAGNETIC-FIELDS, GALAXY CLUSTERS, CHANDRA, Astronomy & Astrophysics
Citation
Su, Y. et al. (2017): Gas Sloshing Regulates and Records the Evolution of the Fornax Cluster. The Astrophysical Journal, 851(1). DOI: 10.3847/1538-4357/aa989e