X-ray exploration of the outskirts of the nearby Centaurus cluster using Suzaku and Chandra. (arXiv:1303.4240v1 [astro-ph.CO]):
We present Suzaku observations of the Centaurus cluster out to 0.95r200,
taken along a strip to the north west. We have also used congruent Chandra
observations of the outskirts to resolve point sources down to a threshold flux
around 7 times lower than that achievable with just Suzaku data, considerably
reducing the systematic uncertainties in the cosmic X-ray background emission
in the outskirts. We find that the temperature decreases by a factor of 2 from
the peak temperature to the outskirts. The entropy profile demonstrates a
central excess (within 0.5r200) over the baseline entropy profile predicted by
simulations of purely gravitational hierarchical structure formation. In the
outskirts the entropy profile is in reasonable agreement with the baseline
entropy profile from Voit et al., but lies slightly below it. We find that the
pressure profile agrees with the universal pressure profile of Arnaud et al.
but lies slightly above it in the outskirts. The excess pressure and decrement
in entropy in the outskirts appear to be the result of an excess in the
measured gas density, possible due to gas clumping biasing the density
measurements high. The gas mass fraction rises and reaches the mean cosmic
baryon fraction at the largest radius studied. The clumping corrected gas mass
fraction agrees with the expected hot gas fraction and with the simulations of
Young et al. We further the analysis of Walker et al. which studied the shapes
of the entropy profiles of the clusters so far explored in the outskirts with
Suzaku. When scaled by the self similar entropy the Suzaku entropy profiles
demonstrate a central excess over the baseline entropy profile, and are
consistent with it at around r500 . However outside r500 the entropy profiles
tend to lie below the baseline entropy profile.
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