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The Hydrangea simulations : galaxy formation in and around massive clusters.

Bahé, Y. M. and Barnes, D. J. and Dalla Vecchia, C. and Kay, S. T. and White, S. D. M. and McCarthy, I. G. and Schaye, J. and Bower, R. G. and Crain, R. A. and Theuns, T. and Jenkins, A. and McGee, S. L. and Schaller, M. and Thomas, P. A. and Trayford, J. W. (2017) 'The Hydrangea simulations : galaxy formation in and around massive clusters.', Monthly notices of the Royal Astronomical Society., 470 (4). pp. 4186-4208.


We introduce the Hydrangea simulations, a suite of 24 cosmological hydrodynamic zoom-in simulations of massive galaxy clusters (M200c = 1014–1015.4 M⊙) with baryon particle masses of ∼106 M⊙. Designed to study the impact of the cluster environment on galaxy formation, they are a key part of the ‘Cluster–EAGLE’ project. They use a galaxy formation model developed for the EAGLE project, which has been shown to yield both realistic field galaxies and hot gas fractions of galaxy groups consistent with observations. The total stellar mass content of the simulated clusters agrees with observations, but central cluster galaxies are too massive, by up to 0.6 dex. Passive satellite fractions are higher than in the field, and at stellar masses Mstar > 1010 M⊙, this environmental effect is quantitatively consistent with observations. The predicted satellite stellar mass function matches data from local cluster surveys. Normalized to total mass, there are fewer low-mass (Mstar ≲ 1010 M⊙) galaxies within the virial radius of clusters than in the field, primarily due to star formation quenching. Conversely, the simulations predict an overabundance of massive galaxies in clusters compared to the field that persists to their far outskirts (>5 r200c). This is caused by a significantly increased stellar mass fraction of (sub-)haloes in the cluster environment, by up to ∼0.3 dex even well beyond r200c. Haloes near clusters are also more concentrated than equally massive field haloes, but these two effects are largely uncorrelated.

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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2017. The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.
Date accepted:05 June 2017
Date deposited:31 August 2017
Date of first online publication:14 June 2017
Date first made open access:31 August 2017

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