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 ( \sim 0.2 keV ) and oxygen abundance ( \sim 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 _ { baryon } \rho _ { critical } , where f _ { baryon } is the baryon fraction of the gas and \rho _ { 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 .