Astronomy & Astrophysics

Free access article

Issue		A&A Volume 398, Number 1, January IV 2003
Page(s)		1 - 12
Section		Extragalactic astronomy
DOI		10.1051/0004-6361:20021584

A&A 398, 1-12 (2003)
DOI: 10.1051/0004-6361:20021584

The detection of diffuse emission in HCG 16 with XMM-Newton

E. Belsole¹, J.-L. Sauvageot¹, T. J. Ponman² and H. Bourdin³

¹ Service d'Astrophysique, CEA Saclay, L'Orme des Merisiers, Bât. 709, 91191 Gif-sur-Yvette Cedex, France
    e-mail: ebelsole@cea.fr; jsauvageot@cea.fr
² School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
    e-mail: tjp@star.sr.bham.ac.uk
³ Observatoire de la Côte d'Azur, BP 4229, 06304 Nice Cedex 4, France
    e-mail: bourdin@obs-nice.fr

(Received 28 January 2002 / Accepted 10 October 2002 )

Abstract
We report results obtained from analysis of the XMM-Newton observation of the compact group of galaxies HCG 16. It is a peculiar system composed of 7 spirals, 6 of which are active, and its nature as a bound system has been much debated. The EPIC camera observations give new insights into the X-ray parameters describing the physical status of the group. We detect diffuse X-ray emission with a rather elliptical morphology which extends to at least a radius of 135 h^-1₅₀ kpc from the group centre. The spectrum within this region is well modelled by a thermal plasma with a temperature of 0.49 $\pm$ 0.17 keV, and a non-zero metallicity. We measure a bolometric X-ray luminosity of $9.6\times 10^$ h^-2₅₀ erg s ^-1which may be only a small fraction of the total luminosity because of the limit in spatial detection arising from the high background level. Despite its low temperature and luminosity, HCG 16 obeys the $L_{\rm X}-T$ relation obtained for brighter galaxy groups even if it lies in a very extreme position. The properties of the diffuse emission confirm the bound nature of HCG 16 even if the gas trapped in the potential well may not yet be virialized. This reopens the debate about the real nature of spiral-dominated galaxy groups, and on their role in a more general cosmological context.

Key words: galaxies: clusters: general -- galaxies: clusters: individual: HCG 16 -- X-ray: galaxies: clusters -- X-rays: general

Offprint request: E. Belsole, ebelsole@cea.fr

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