The mass distribution in the outskirts of clusters of galaxies as a probe of the theory of gravity

¹ Department of Astronomy and Physics, Saint Mary’s University, 923 Robie Street, Halifax B3H3C3, Canada
e-mail: michele.pizzardo@smu.ca
² Dipartimento di Fisica, Università di Torino, Via P. Giuria 1, 10125 Torino, Italy
³ Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Torino, Via P. Giuria 1, 10125 Torino, Italy
⁴ Department of Physics and Astronomy, Western Washington University, Bellingham, WA 98225, USA

Received: 7 July 2022
Accepted: 24 November 2023

Abstract

We show that ς, the radial location of the minimum in the differential radial mass profile M′(r) of a galaxy cluster, can probe the theory of gravity. We derived M′(r) of the dark matter halos of galaxy clusters from N-body cosmological simulations that implement two different theories of gravity: standard gravity in the ΛCDM model, and f(R). We extracted 49 169 dark matter halos in 11 redshift bins in the range 0 ≤ z ≤ 1 and in three different mass bins in the range 0.9 < M_200c/10¹⁴ h⁻¹ M_⊙ < 11. We investigated the correlation of ς with the redshift and the mass accretion rate (MAR) of the halos. We show that ς decreases from ∼3R_200c to ∼2R_200c when z increases from 0 to 1 in the ΛCDM model. At z ∼ 0.1, ς decreases from 2.8R_200c to ∼2.5R_200c when the MAR increases from ∼10⁴ h⁻¹ M_⊙ yr⁻¹ to ∼2 × 10⁵ h⁻¹ M_⊙ yr⁻¹. In the f(R) model, ς is ∼15% larger than in ΛCDM. The median test shows that for samples of ≳400 dark matter halos at z ≤ 0.8, ς is able to distinguish between the two theories of gravity with a p-value ≲10⁻⁵. Upcoming advanced spectroscopic and photometric programs will allow a robust estimation of the mass profile of enormous samples of clusters up to large clustercentric distances. These samples will allow us to statistically exploit ς as probe of the theory of gravity, which complements other large-scale probes.