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

Wu, Hao-Yi; Evrard, August E; Hahn, Oliver; Martizzi, Davide; Teyssier, Romain; Wechsler, Risa H (2015). Rhapsody-G simulations: galaxy clusters as baryonic closed boxes and the covariance between hot gas and galaxies. Monthly Notices of the Royal Astronomical Society, 452(2):1982-1991.

## 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 $0.02 (\Delta_c/100)^{0.6}$, 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% scatter in total halo mass.

## 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 $0.02 (\Delta_c/100)^{0.6}$, 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% scatter in total halo mass.

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Item Type: Journal Article, refereed, original work 07 Faculty of Science > Institute for Computational Science 530 Physics English September 2015 22 Feb 2016 14:16 14 Feb 2018 11:12 Oxford University Press 0035-8711 This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2015 The Authors Published by Oxford University Press on behalf of Royal Astronomical Society. All rights reserved. Green Publisher DOI. An embargo period may apply. https://doi.org/10.1093/mnras/stv1434 arXiv:1503.03924v2