Discovery of an absorbed cluster of galaxies (XMMU J183225.4-103645) close to the Galactic plane with XMM-Newton

¹ Astrophysics Division, Space Science Department of ESA, ESTEC, Postbus 299, 2200 AG Noordwijk, The Netherlands
² Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK

Corresponding author: J. Nevalainen, jnevalai@astro.estec.esa.nl

Received: 12 March 2001
Accepted: 3 May 2001

Abstract

During an XMM-Newton observation of the galactic supernova remnant G21.5-09 a bright, previously uncatalogued, source (XMMU J183225.4-103645) was detected 18´from G21.5-09. The European Photon Imaging Camera data inside 1´(180 kpc) radius are consistent with a source at a redshift of with an optically thin thermal spectrum of temperature keV and a metal abundance of solar. This model gives a 2-10 keV luminosity of erg s^-1. These characteristics, as well as the source extent of 20 (350 kpc), and the surface brightness profile are consistent with emission from the central region of a moderately rich cluster containing a cooling flow with mass flow rate of - yr^-1. The absorption is atom cm^-2, 5 times that inferred from low-resolution HI data but consistent with higher spatial resolution infrared dust extinction estimates. XMMU J183225.4-103645 is not visible in earlier ROSAT observations due to high amount of absorption. This discovery demonstrates the capability of XMM-Newton to map the cluster distribution close to the Galactic plane, where few such systems are known. The ability of XMM-Newton to determine cluster redshifts to 1% precision at is especially important in optically crowded and absorbed fields such as close to the Galactic plane, where the optical redshift measurements of galaxies are difficult.