Living with Neighbors. II. Statistical Analysis of Flybys and Mergers of Dark Matter Halos in Cosmological Simulations. (arXiv:1911.11782v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+An_S/0/1/0/all/0/1">Sung-Ho An</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kim_J/0/1/0/all/0/1">Juhan Kim</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Moon_J/0/1/0/all/0/1">Jun-Sung Moon</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yoon_S/0/1/0/all/0/1">Suk-Jin Yoon</a>
We present a statistical analysis of flybys of dark matter halos compared to
mergers using cosmological $N$-body simulations. We mainly focus on
gravitationally interacting target halos with mass of
$10^{10.8}-10^{13.0}h^{-1}M_{odot}$, and their neighbors are counted only when
the mass ratio is 1:3$-$3:1 and the distance is less than the sum of the virial
radii of target and neighbor. The neighbors are divided into the flyby or
merger samples if the pair’s total energy is greater or smaller, respectively,
than the capture criterion with consideration of dynamical friction. The main
results are as follows: (a) The flyby fraction increases by up to a factor of
50 with decreasing halo mass and by up to a factor of 400 with increasing
large-scale density, while the merger fraction does not show any significant
dependencies on these two parameters; (b) The redshift evolution of the flyby
fraction is twofold, increasing with redshift at $0
$z=0sim4$; (c) The multiple interactions with two or more neighbors are on
average flyby-dominated, and their fraction has a mass and environment
dependence similar to that for the flyby fraction; (d) Given that flybys
substantially outnumber mergers toward $z=0$ (by a factor of five) and the
multiple interactions are flyby-dominated, the flyby’s contribution to galactic
evolution is stronger than ever at the present epoch, especially for less
massive halos and in the higher density environment. We propose a scenario that
connects the evolution of the flyby and merger fractions to the hierarchical
structure formation process.
We present a statistical analysis of flybys of dark matter halos compared to
mergers using cosmological $N$-body simulations. We mainly focus on
gravitationally interacting target halos with mass of
$10^{10.8}-10^{13.0}h^{-1}M_{odot}$, and their neighbors are counted only when
the mass ratio is 1:3$-$3:1 and the distance is less than the sum of the virial
radii of target and neighbor. The neighbors are divided into the flyby or
merger samples if the pair’s total energy is greater or smaller, respectively,
than the capture criterion with consideration of dynamical friction. The main
results are as follows: (a) The flyby fraction increases by up to a factor of
50 with decreasing halo mass and by up to a factor of 400 with increasing
large-scale density, while the merger fraction does not show any significant
dependencies on these two parameters; (b) The redshift evolution of the flyby
fraction is twofold, increasing with redshift at $0<z<1$ and remaining constant
at $z>1$, while the merger fraction increases monotonically with redshift at
$z=0sim4$; (c) The multiple interactions with two or more neighbors are on
average flyby-dominated, and their fraction has a mass and environment
dependence similar to that for the flyby fraction; (d) Given that flybys
substantially outnumber mergers toward $z=0$ (by a factor of five) and the
multiple interactions are flyby-dominated, the flyby’s contribution to galactic
evolution is stronger than ever at the present epoch, especially for less
massive halos and in the higher density environment. We propose a scenario that
connects the evolution of the flyby and merger fractions to the hierarchical
structure formation process.
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