Journal
ASTRONOMY & ASTROPHYSICS
Volume 570, Issue -, Pages -Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361/201424259
Keywords
galaxies: groups: general; galaxies: clusters: general; galaxies: clusters: intracluster medium; X-rays: galaxies: clusters; large-scale structure of Universe
Categories
Funding
- ESA Member States
- NASA
- US NSF [AST-1211595]
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [1211595] Funding Source: National Science Foundation
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Structure formation in the current Universe operates through the accretion of group-scale systems onto massive clusters. The detection and study of such accreting systems is crucial to understand the build-up of the most massive virialized structures we see today. We report the discovery with XMM-Newton of an irregular X-ray substructure in the outskirts of the massive galaxy cluster Abell 2142. The tip of the X-ray emission coincides with a concentration of galaxies. The bulk of the X-ray emission of this substructure appears to be lagging behind the galaxies and extends over a projected scale of at least 800 kpc. The temperature of the gas in this region is 1.4 keV, which is a factor of similar to 4 lower than the surrounding medium and is typical of the virialized plasma of a galaxy group with a mass of a few 10(13) M-circle dot. For this reason, we interpret this structure as a galaxy group in the process of being accreted onto the main dark-matter halo. The X-ray structure trailing behind the group is due to gas stripped from its original dark-matter halo as it moves through the intracluster medium (ICM). This is the longest X-ray trail reported to date. For an infall velocity of similar to 1200 km s(-1) we estimate that the stripped gas has been surviving in the presence of the hot ICM for at least 600 Myr, which exceeds the Spitzer conduction timescale in the medium by a factor of greater than or similar to 400. Such a strong suppression of conductivity is likely related to a tangled magnetic field with small coherence length and to plasma microinstabilities. The long survival time of the low-entropy intragroup medium suggests that the infalling material can eventually settle within the core of the main cluster.
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