X-ray Spectroscopy of the Virgo Cluster out to the Virial Radius

TL;DR

This study uses X-ray observations to analyze the Virgo Cluster out to its virial radius, revealing insights into its density, temperature, entropy profiles, and metal enrichment, with implications for understanding cluster outskirts and gas clumping.

Contribution

First detailed X-ray analysis of a modest, dynamically young cluster out to the virial radius, revealing unexpected shallow density and entropy profiles and evidence of metal enrichment.

Findings

Density profile is a shallow power-law with index 1.21.

Temperature drops by about 60% from center to virial radius.

Metallicity is enriched to at least 0.1 Solar at large radii.

Abstract

We present results from the analysis of a mosaic of thirteen XMM-Newton pointings covering the Virgo Cluster from its center northwards out to a radius r~1.2 Mpc (~4.5 degrees), reaching the virial radius and beyond. This is the first time that the properties of a modestly sized (M_vir~1.4e14 M_sun, 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 with index 1.21+/-0.12. In the radial range of 0.3r_vir<r<r_vir, the best fit temperature drops by roughly 60 per cent. Within a radius r<450 kpc, the entropy profile has an approximate power-law form with index 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 Solar.