Chandra Observation of Abell 1142: A Cool-Core Cluster Lacking a Central Brightest Cluster Galaxy?

Abstract

Abell1142 is a low-mass galaxy cluster at low redshift containing two comparable brightest cluster galaxies (BCGs) resembling a scaled-down version of the Coma Cluster. Our Chandra analysis reveals an X-ray emission peak, roughly 100 kpc away from either BCG, which we identify as the cluster center. The emission center manifests itself as a second beta-model surface brightness component distinct from that of the cluster on larger scales. The center is also substantially cooler and more metal-rich than the surrounding intracluster medium (ICM), which makes Abell1142 appear to be a cool-core cluster. The redshift distribution of its member galaxies indicates that Abell1142 may contain two subclusters, each of which contain one BCG. The BCGs are merging at a relative velocity of ≈1200 km s −1 . This ongoing merger may have shock-heated the ICM from ≈2 keV to above 3 keV, which would explain the anomalous L X -T X scaling relation for this system. This merger may have displaced the metal-enriched "cool core" of either of the subclusters from the BCG. The southern BCG consists of three individual galaxies residing within a radius of 5 kpc in projection. These galaxies should rapidly sink into the subcluster center due to the dynamical friction of a cuspy cold dark matter halo.

XMM-Newton and Chandra Observations of the Unidentified Fermi-LAT Source 3FGL J1016.5–6034: A Young Pulsar with a Nebula?

“…On the other hand, it is possible that the large scale extended emission is unrelated to CXOU J101546 and could belong to a background galaxy cluster that happens to be in the field-of-view. The spectrum of the large-scale extended emission is equally well fit by a bremsstrahlung model with a temperature of 2.4 keV, which is consistent with the measured temperatures of hot gas in galaxy clusters (see e.g., Su et al 2016;Tchernin et al 2016). Deeper Chandra observations are needed to resolve the large scale emission and to understand how it is related, if at all, to CXOU J101546.…”

Capturing the 3d Motion of an Infalling Galaxy via Fluid Dynamics

“…Our knowledge of fluid dynamics has been widely used to infer cluster gas motion. One of the best known examples is the application of the Rankine-Hugoniot jump conditions: the gas properties on both sides of a shock wave in a one-dimensional flow can be used to infer the infalling speed of a substructure (e.g, Su et al 2016;Vikhlinin et al 2001;Markevitch et al 2002). Moreover, cosmological applications of galaxy clusters require accurate measurements of cluster masses, which also rely on the hydrostatic approximation of ICM (e.g., Buote et al 2016).…”

Independent Evidence for Earlier Formation Epochs of Fossil Groups of Galaxies through the Intracluster Light: The Case for RX J100742.53+380046.6

“…It would likely require a preexistent high abundance gradient in at least one of the premerging systems. A situation similar to the case of A1142 (Su et al 2016), where the merging BCGs would subsequently settle in the high metal core. Even though metal transport through BCG sloshing have been observed (e.g., Dupke et al 2007;Simionescu et al 2010), it is not physically implausible that central abundance gradients could survive mergers, even if the cool cores were destroyed, given the different nature of the mechanisms of thermalization and chemical mixing and the inefficiency with which post-merging sloshing mixes the gas Ghizzardi et al (2014).…”