Cold fronts and metal anisotropies in the X-ray cool core of the galaxy cluster Zw 1742+3306

¹ INAF, Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
e-mail: stefano.ettori@oabo.inaf.it
² INFN, Sezione di Bologna, viale Berti Pichat 6/2, 40127 Bologna, Italy
³ INAF, IASF, via E. Bassini 15, 20133 Milano, Italy
⁴ University of California Irvine, 4129, Frederick Reines Hall, Irvine, CA 92697-4575, USA
⁵ Physics and Astronomy Department, University of Bologna, via Ranzani 1, 40127 Bologna, Italy
⁶ Harvard-Smithsonian centre for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁷ Max Planck Institute for Astrophysics, Karl-Schwarzschild-Strasse 1, 85741 Garching, Germany
⁸ Department of Physics, University of Durham, south Road, Durham, DH1 3LE, UK

Received: 15 January 2013
Accepted: 14 May 2013

Abstract

Context. In recent years, our understanding of the cool cores of galaxy clusters has changed. Once thought to be relatively simple places where gas cools and flows towards the centre, now they are believed to be very dynamic places where heating from the central active galactic nucleus (AGN) and cooling, as inferred from active star formation, molecular gas, and Hα nebulosity, find an uneasy energetic balance.

Aims. We want to characterize the X-ray properties of the nearby cool-core cluster Zw 1742+3306, selected because it is bright at X-ray (with a flux greater than 10^-11 erg s^-1 cm^-2 in the 0.1–2.4 keV band) and Hα wavelengths (Hα luminosity >10⁴⁰ erg s^-1).

Methods. We used Chandra data to analyse the spatial and spectral properties of the cool core of Zw 1742+3306, a galaxy cluster at z = 0.0757 that emits in Hα and presents the brightest central galaxy located in a diffuse X-ray emission with multiple peaks in surface brightness.

Results. We show that the X-ray cool core of the galaxy cluster Zw 1742+3306 is thermodynamically very active with evidence of cold fronts and a weak shock in the surface brightness map and of an apparently coherent, elongated structure with metallicity greater than the value measured in the surrounding ambient gas by about 50%. This anisotropic structure is 280 × 90 kpc² and is aligned with the cold fronts and with the X-ray emission on larger scales. We suggest that all these peculiarities in the X-ray emission of Zw 1742+3306 are either a very fine-tuned output of a sloshing gas in the cluster core or the product of a metal-rich outflow from the central AGN.