Halo velocity profiles in screened modified gravity theories

TL;DR

This paper explores how screened modified gravity theories like Symmetron and Chameleon f(R) affect peculiar velocity fields, identifying three regimes with distinct observational signatures using N-body simulations.

Contribution

It introduces a detailed analysis of velocity profiles in screened modified gravity models, highlighting three distinct screening regimes and their observational implications.

Findings

Identification of fully, partially, and unscreened regimes in velocity profiles.

Partially screened regime shows unique velocity deviations at larger radii.

Degeneracy in the unscreened regime complicates observational detection.

Abstract

Screened modified gravity predicts potentially large signatures in the peculiar velocity field that makes it an interesting probe to test gravity on cosmological scales. We investigate the signatures induced by the Symmetron and a Chameleon $f(R)$ model in the peculiar velocity field using $N$-body simulations. By studying fifth force and halo velocity profiles we identify three general categories of effects found in screened modified gravity models: a fully screened regime where we recover $\Lambda$CDM to high precision, an unscreened regime where the fifth force is in full operation, and, a partially screened regime where screening occurs in the inner part of a halo, but the fifth force is active at larger radii. These three regimes can be pointed out very clearly by analyzing the deviation in the maximum cluster velocity. Observationally, the partially screened regime is of particular interest since an uniform increase of the gravitational force - as present in the unscreened regime - is degenerate with the (dynamical) halo mass estimate, and, thus, hard to detect.