EDP Sciences
Free access
Volume 374, Number 1, July IV 2001
Page(s) 66 - 72
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20010649

A&A 374, 66-72 (2001)
DOI: 10.1051/0004-6361:20010649

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

J. Nevalainen1, D. Lumb1, S. dos Santos2, H. Siddiqui1, G. Stewart2 and A. N. Parmar1

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

(Received 12 March 2001 / Accepted 3 May 2001 )

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 h50-1 kpc) radius are consistent with a source at a redshift of $0.1242 \pm ^{0.0003}_{0.0022}$ with an optically thin thermal spectrum of temperature $5.8 \pm 0.6$ keV and a metal abundance of $0.60 \pm 0.10$ solar. This model gives a 2-10 keV luminosity of $3.5^{+0.8}_{-0.4} h_{50}^{-2} \times 10^{44}$ erg s-1. These characteristics, as well as the source extent of 2$\farcm$0 (350 h50-1 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 ${\sim \! 400}$- ${600} M_{\odot}$ yr-1. The absorption is $(7.9 \pm 0.5) \times 10^{22}$ 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 z = 0.1 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.

Key words: galaxies: clusters: individual: XMMU J183225.4 -- 103645 -- galaxies: intergalactic medium -- X-rays: galaxies: clusters

Offprint request: J. Nevalainen, jnevalai@astro.estec.esa.nl

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© ESO 2001