Turnaround radius of galaxy clusters in Nbody simulations
Abstract
Aims: We use Nbody simulations to examine whether a characteristic turnaround radius, as predicted from the spherical collapse model in a ΛCDM Universe, can be meaningfully identified for galaxy clusters in the presence of full threedimensional effects.
Methods: We use The Dark Sky Simulations and IllustrisTNG darkmatteronly cosmological runs to calculate radial velocity profiles around collapsed structures, extending out to many times the virial radius R_{200}. There, the turnaround radius can be unambiguously identified as the largest nonexpanding scale around a center of gravity.
Results: We find that: (a) a single turnaround scale can meaningfully describe strongly nonspherical structures. (b) For halos of masses M_{200} > 10^{13} M_{⊙}, the turnaround radius R_{ta} scales with the enclosed mass M_{ta} as M_{ta}^{1/3}, as predicted by the spherical collapse model. (c) The deviation of R_{ta} in simulated halos from the spherical collapse model prediction is relatively insensitive to halo asphericity. Rather, it is sensitive to the tidal forces due to massive neighbors when these are present. (d) Halos exhibit a characteristic average density within the turnaround scale. This characteristic density is dependent on cosmology and redshift. For the present cosmic epoch and for concordance cosmological parameters (Ω_{m} ∼ 0.3; Ω_{Λ} ∼ 0.7) turnaround structures exhibit a density contrast with the matter density of the background Universe of δ ∼ 11. Thus, R_{ta} is equivalent to R_{11}  in a way that is analogous to defining the "virial" radius as R_{200}  with the advantage that R_{11} is shown in this work to correspond to a kinematically relevant scale in Nbody simulations.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 July 2020
 DOI:
 10.1051/00046361/201937337
 arXiv:
 arXiv:1912.08216
 Bibcode:
 2020A&A...639A.122K
 Keywords:

 largescale structure of Universe;
 methods: numerical;
 galaxies: clusters: general;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 Submitted to A&