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Published September 11, 2015 | Published
Journal Article Open

Rhapsody-G simulations: galaxy clusters as baryonic closed boxes and the covariance between hot gas and galaxies

Abstract

Within a sufficiently large cosmic volume, conservation of baryons implies a simple 'closed box' view in which the sum of the baryonic components must equal a constant fraction of the total enclosed mass. We present evidence from RHAPSODY-G hydrodynamic simulations of massive galaxy clusters that the closed-box expectation may hold to a surprising degree within the interior, non-linear regions of haloes. At a fixed halo mass, we find a significant anti-correlation between hot gas mass fraction and galaxy mass fraction (cold gas + stars), with a rank correlation coefficient of −0.69 within R_(500c). Because of this anti-correlation, the total baryon mass serves as a low-scatter proxy for total cluster mass. The fractional scatter of total baryon fraction scales approximately as 0.02(Δ_c/100)^(0.6), while the scatter of either gas mass or stellar mass is larger in magnitude and declines more slowly with increasing radius. We discuss potential observational tests using cluster samples selected by optical and hot gas properties; the simulations suggest that joint selection on stellar and hot gas has potential to achieve 5 per cent scatter in total halo mass.

Additional Information

© 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 June 25. Received 2015 June 21. In original form 2014 December 30. First published online July 21, 2015. We thank Steve Allen, Adam Mantz, Truong Nhut, Elena Rasia, and Yuanyuan Zhang for useful discussions. We thank Peter Behroozi for kindly making his ROCKSTAR-GALAXIES code available to us for further modifications. HW acknowledges the support by the U.S. Department of Energy under contract number DE-FG02-95ER40899. OH acknowledges support from the Swiss National Science Foundation through the Ambizione fellowship. DM acknowledges support from the Swiss National Science Foundation. RW received support from the U.S. Department of Energy contract to SLAC no. DE-AC02-76SF0051. This work was supported by a grant from the Swiss National Supercomputing Centre (CSCS) under project ID s416.

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