Witnessing the growth of the nearest galaxy cluster: thermodynamics of the Virgo Cluster outskirts

Simionescu, A. and Werner, Norbert and Mantz, A. and Allen, S. W. and Urban, O. (2017) Witnessing the growth of the nearest galaxy cluster: thermodynamics of the Virgo Cluster outskirts. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 469 (2). pp. 1476-1495. ISSN 0035-8711

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Abstract

We present results from Suzaku Key Project observations of the Virgo Cluster, the nearest galaxy cluster to us, mapping its X-ray properties along four long 'arms' extending beyond the virial radius. The entropy profiles along all four azimuths increase with radius, then level out beyond ∼0.5r<SUB>200</SUB>, while the average pressure at large radii exceeds Planck Sunyaev-Zel'dovich measurements. These results can be explained by enhanced gas density fluctuations (clumping) in the cluster's outskirts. Using a standard Navarro, Frenk and White model, we estimate a virial mass, radius and concentration parameter of M<SUB>200</SUB> = 1.05 ± 0.02 × 10<SUP>14</SUP> M<SUB>⊙</SUB>, r<SUB>200</SUB> = 974.1 ± 5.7 kpc and c = 8.8 ± 0.2, respectively. The inferred cumulative baryon fraction exceeds the cosmic mean at r ∼ r<SUB>200</SUB> along the major axis, suggesting enhanced gas clumping possibly sourced by a candidate large-scale structure filament along the north-south direction. The Suzaku data reveal a large-scale sloshing pattern, with two new cold fronts detected at radii of 233 and 280 kpc along the western and southern arms, respectively. Two high-temperature regions are also identified 1 Mpc towards the south and 605 kpc towards the west of M87, likely representing shocks associated with the ongoing cluster growth. Although systematic uncertainties in measuring the metallicity for low-temperature plasma remain, the data at large radii appear consistent with a uniform metal distribution on scales of ∼90 × 180 kpc and larger, providing additional support for the early chemical enrichment scenario driven by galactic winds at redshifts of 2-3.

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