X-ray spectroscopy of the Virgo Cluster out to the virial radius

• Published in: Monthly notices of the Royal Astronomical Society Vol. 414; no. 3; pp. 2101 - 2111
• Main Authors: Urban, O., Werner, N., Simionescu, A., Allen, S. W., Böhringer, H.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-07-2011; Wiley-Blackwell; Oxford University Press
• Subjects: Approximation; Astronomy; Clusters; Density; Earth, ocean, space; Entropy; Exact sciences and technology; Flattening; Hydrostatics; Metallicity; Spectrum analysis; Stars & galaxies; X-ray astronomy; X-rays: galaxies: clusters; X-rays: individual: Virgo; XMM (spacecraft); X-rays: galaxies: clusters; X-rays: individual: Virgo; X ray cluster of galaxies; Young cluster; Flattening; Metallicity; Hydrostatic equilibrium; Cosmic x-ray sources; Entropy; X-ray spectroscopy; Star clusters; Power law
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2011.18526.x

We present results from the analysis of a mosaic of 13 XMM-Newton pointings covering the Virgo Cluster from its centre northwards out to a radius r∼ 1.2 Mpc (∼4°.5), reaching the virial radius and beyond. This is the first time that the properties of a modestly sized (M
vir∼ 1.4 × 1014 M⊙, kT∼ 2.3 keV), dynamically young cluster have been studied out to the virial radius. The density profile of the cluster can be described by a surprisingly shallow power-law n
e∝r
−β with index β= 1.21 ± 0.12. In the radial range of 0.3r
vir < r < r
vir, the best-fitting temperature drops by roughly 60 per cent. Within a radius r < 450 kpc, the entropy profile has an approximate power law form K∝r
1.1, as expected for gravitationally collapsed gas in hydrostatic equilibrium. Beyond r∼ 450 kpc, however, the temperature and metallicity drop abruptly, and the entropy profile becomes flatter, staying consistently below the expected value by a factor of 2-2.5. The most likely explanation for the unusually shallow density profile and the flattening of entropy at large radius is clumping in the ICM. Our data provide direct observational evidence that the ICM is enriched by metals all the way to r
200 to at least Z= 0.1 Z⊙.