# Chameleon $f(R)$ gravity on the Virgo cluster scale

Moran, Christine Corbett; Teyssier, Romain; Li, Baojiu (2015). Chameleon $f(R)$ gravity on the Virgo cluster scale. Monthly Notices of the Royal Astronomical Society, 448(1):307-327.

## Abstract

Models of modified gravity offer promising alternatives to the concordance $\Lambda$CDM cosmology to explain the late-time acceleration of the universe. A popular such model is $f(R)$ gravity, in which the Ricci scalar in the Einstein-Hilbert action is replaced by a general function of it. We study the $f(R)$ model of Hu &amp; Sawicki (2007), which recovers standard General Relativity in high density regimes, while reproducing the desired late-time acceleration at cosmological scales. We run a suite of high resolution zoom simulations using the ECOSMOG code to examine the effect of $f(R)$ gravity on the properties of a halo that is analogous to the Virgo cluster. We show that the velocity dispersion profiles can potentially discriminate between $f(R)$ models and $\Lambda$CDM, and provide complementary analysis of lensing signal profiles to explore the possibility to further distinguish the different $f(R)$ models. Our results confirm the techniques explored by Cabre et al. (2012) to quantify the effect of environment in the behavior of $f(R)$ gravity, and we extend them to study halo satellites at various redshifts. We find that the modified gravity effects in our models are most observable at low redshifts, and that effects are generally stronger for satellites far from the center of the main halo. We show that the screening properties of halo satellites trace very well that of dark matter particles, which means that low-resolution simulations in which subhalos are not very well resolved can in principle be used to study satellite properties. We discuss observables, particularly for halo satellites, that can potentially be used to constrain the observational viability of $f(R)$
gravity.

## Abstract

Models of modified gravity offer promising alternatives to the concordance $\Lambda$CDM cosmology to explain the late-time acceleration of the universe. A popular such model is $f(R)$ gravity, in which the Ricci scalar in the Einstein-Hilbert action is replaced by a general function of it. We study the $f(R)$ model of Hu &amp; Sawicki (2007), which recovers standard General Relativity in high density regimes, while reproducing the desired late-time acceleration at cosmological scales. We run a suite of high resolution zoom simulations using the ECOSMOG code to examine the effect of $f(R)$ gravity on the properties of a halo that is analogous to the Virgo cluster. We show that the velocity dispersion profiles can potentially discriminate between $f(R)$ models and $\Lambda$CDM, and provide complementary analysis of lensing signal profiles to explore the possibility to further distinguish the different $f(R)$ models. Our results confirm the techniques explored by Cabre et al. (2012) to quantify the effect of environment in the behavior of $f(R)$ gravity, and we extend them to study halo satellites at various redshifts. We find that the modified gravity effects in our models are most observable at low redshifts, and that effects are generally stronger for satellites far from the center of the main halo. We show that the screening properties of halo satellites trace very well that of dark matter particles, which means that low-resolution simulations in which subhalos are not very well resolved can in principle be used to study satellite properties. We discuss observables, particularly for halo satellites, that can potentially be used to constrain the observational viability of $f(R)$
gravity.

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Item Type: Journal Article, refereed, original work 07 Faculty of Science > Institute for Computational Science 530 Physics English March 2015 22 Feb 2016 15:00 05 Apr 2016 20:05 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. Publisher DOI. An embargo period may apply. https://doi.org/10.1093/mnras/stu2757 arXiv:1408.2856

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