Living with Neighbors. II. Statistical Analysis of Flybys and Mergers of Dark Matter Halos in Cosmological Simulations

Sung Ho An, Juhan Kim, Jun Sung Moon, Suk Jin Yoon

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)


We present a statistical analysis of the flybys of dark matter halos compared to mergers, using cosmological N-body simulations. We mainly focus on gravitationally interacting target halos with mass of 1010.8-1013.0 h -1 M o&dot;, 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 = 0 ∼ 4; (c) 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; and (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.

Original languageEnglish
Article number59
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 2019 Dec 10

Bibliographical note

Publisher Copyright:
© 2019. The American Astronomical Society. All rights reserved..

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


Dive into the research topics of 'Living with Neighbors. II. Statistical Analysis of Flybys and Mergers of Dark Matter Halos in Cosmological Simulations'. Together they form a unique fingerprint.

Cite this