Astronomy & Astrophysics

Free access article

A&A 410, 777-784 (2003)
DOI: 10.1051/0004-6361:20031319

XMM-Newton discovery of an X-ray filament in Coma

A. Finoguenov¹, U. G. Briel¹ and J. P. Henry²

¹ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany
² Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, Hawaii 96822, USA

(Received 12 January 2003 / Accepted 12 August 2003)

Abstract
XMM-Newton observations of the outskirts of the Coma cluster of galaxies confirm the existence of a soft X-ray excess claimed previously and show it comes from warm thermal emission. Our data provide a robust estimate of its temperature (~0.2 keV) and oxygen abundance (~0.1 solar). Using a combination of XMM-Newton and ROSAT All-Sky Survey data, we rule out a Galactic origin of the soft X-ray emission. Associating this emission with a 20 Mpc region in front of Coma, seen in the skewness of its galaxy velocity distribution, yields an estimate of the density of the warm gas of $\sim$ 50 $f_{\rm baryon} \rho_{\rm critical}$ , where $f_{\rm baryon}$ is the baryon fraction and $\rho_{\rm critical}$ is the critical density needed to halt the expansion of the universe. Our measurement of the gas mass associated with the warm emission strongly support its nonvirialized nature, suggesting that we are observing the warm-hot intergalactic medium (WHIM). Our measurements provide a direct estimate of the O, Ne and Fe abundance of the WHIM. Differences with the reported Ne/O ratio for some OVI absorbers hints at a different origin of the OVI absorbers and the Coma filament. We argue that the Coma filament has likely been preheated, but at a substantially lower level compared to what is seen in the outskirts of groups. The thermodynamic state of the gas in the Coma filament reduces the star-formation rate in the embedded spiral galaxies, providing an explanation for the presence of passive spirals observed in this and other clusters.

Key words: galaxies: clusters: individual: Coma -- cosmology: observations -- intergalactic medium -- large-scale structure of universe

Offprint request: A. Finoguenov, alexis@xray.mpe.mpg.de

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