Testing gravity using cosmic voids

By Yan-Chuan Cai, N. Padilla, Baojiu Li. 2014

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We explore voids in dark matter and halo fields from simulatio ns ofCDM and Hu-Sawicki f(R) models. In f(R) gravity, dark matter void abundances are greater than that of general relativity (GR). However, when using haloes to identify voids, the differences of void abun- dances become much smaller, but can still be told apart, in principle, at the 2,6 and 14σ level for the f(R) model parameter amplitudes of |fR0| = 10 6 , 10 5 and 10 4 . In contrast to the naive expectation, the abundance of large voids found using haloes in f(R) gravity is lower than in GR. The more efficient halo formation in underdense re gions makes f(R) voids less empty of haloes. This counter intuitive result suggests tha t voids are not necessarily emptier in f(R) if one looks at galaxies or groups in voids. Indeed, the halo number density profiles of voids are not distinguishable from GR. However, the same f(R) voids are more empty of dark matter. This can in principle be observed by weak gravitational lensing of voids, for which the combination of a spec-z and a photo-z survey over the same sky is necessary. For a volume of 1 (Gpc/h) 3 , neglecting the lensing shape noise, |fR0| = 10 5 and 10 4 may be distinguished from GR using the lensing tangential shear signal around voids by 4 and 8σ. We find that the line-of-sight projection of large-scale str ucture is the main systematics that limits the significance of this signal, limiting the constra ining power for |fR0| = 10 6 . We expect that this can be overcome with larger volume. The halo void abundance being smaller and the steepening of dark matter void profiles in f(R) models are unique features that can be combined to break the degeneracy between |fR0| and σ8. The outflow of mass from void centers are 5%, 15% and 35% faster inf(R) for |fR0| = 10 6 , 10 5 and 10 4 , with little de- pendence on the tracers used. The velocity dispersions are greater than that in GR by similar amounts. The absolute differences are greater for large voids. Model differences in velocity profiles imply potential powerful constraints of the model i n phase space and in redshift space.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/e228bb6bbf9a785ab1bfc53142f6e5b189b3c1be