The Unrelaxed Dynamical Structure of the Galaxy Cluster Abell 85

Abstract

For the first time, we explore the dynamics of the central region of a galaxy cluster within r 500 ∼600 h −1 kpc from its center by combining optical and X-ray spectroscopy. We use (1) the caustic technique, whichidentifies the cluster substructures and their galaxy members with optical spectroscopic data, and (2) the X-ray redshift fitting procedure, which estimates the redshift distribution of the intracluster medium (ICM). We use the spatial and redshift distributions of the galaxies and of the X-ray-emitting gas to associate the optical substructures to the X-ray regions. When we apply this approach to Abell 85 (A85), a complex dynamic structure of A85 emerges from our analysis: a galaxy group, with redshift z=0.0509±0.0021 is passing through the cluster center along the line of sight dragging part of the ICM present in the cluster core; two additional groups, at redshift z=0.0547±0.0022 and z=0.0570±0.0020, are going through the cluster in opposite directions, almost perpendicularly to the line of sight, and have substantially perturbed the dynamics of the ICM. An additional group in the outskirts of A85, at redshift z=0.0561±0.0023, is associated with a secondary peak of X-ray emission, at redshift = -+ z 0.0583 0.0047 0.0039 . Although our analysis and results on A85 need to be confirmed by high-resolution spectroscopy, they demonstrate how our new approach can be a powerful tool to constrain the formation history of galaxy clusters by unveiling their central and surrounding structures.

Deep spectroscopy of nearby galaxy clusters – IV. The quench of the star formation in galaxies in the infall region of Abell 85

“…This large scale structure suggests that the process of the mass assembly in A 85 is still on going. This is also suggested by the observational evidences of galaxy substructure and recent mergers in the cluster (Ramella et al 2007;Aguerri & Sánchez-Janssen 2010;Yu et al 2016). Figure 1 shows the velocity distribution of the galaxies in the direction of A 85 with radial velocity smaller than 32000 km s −1 , and within 1.4 r 200 .…”

Physical properties of SDSS satellite galaxies in projected phase space

“…Further observational evidence comes from sub-structures identified in the velocity field of galaxy clusters, such as Virgo, Fornax, Coma, Abell 85, Abell 2744 and Hydra A/A780, which have been interpreted as accreted lower-mass groups (e.g. Fitchett & Webster 1987, Colless & Dunn 1996, Petrosian et al 1998, Zabludoff & Mulchaey 1998, Drinkwater et al 2001, Edwards et al 2002, Adami et al 2005, Boselli et al 2014, De Grandi et al 2016, Jauzac et al 2016, Oldham & Evans 2016, Yu et al 2016, Lisker et al 2018).…”

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

“…The commonly accepted scenario is that clusters form and evolve via accretion and merging of smaller halos. This scenario is suggested by many dynamical features observed in clusters: substructures in the galaxy distribution (Geller & Beers 1982;Wen & Han 2013;Guennou et al 2014;Girardi et al 2015;Zarattini et al 2016); apparent global rotation of clusters (Hwang & Lee 2007;Manolopoulou & Plionis 2017); clumpy distributions (Gutierrez & Krawczynski 2005;Parekh et al 2015;Yu et al 2016;Parekh et al 2017) and bow shocks (Markevitch et al 2002(Markevitch et al , 2005 in the intracluster medium (ICM) observed in X-rays; the elongated or peculiar distributions of radio emission Govoni et al 2012;Riseley et al 2017;Rajpurohit et al 2018); the substructure distribution of the dark matter, inferred from gravitational lensing observations (Okabe & Umetsu 2008;Okabe et al 2014;Grillo et al 2015;Caminha et al 2017). In addition, "cold fronts" are frequently observed in X-ray images of clusters (Markevitch et al 2000;Sanders et al 2005Ichinohe et al 2017), including some regular and relaxed clusters Clarke et al 2004).…”