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Statistics of galaxy mergers: bridging the gap between theory and observation

Huško, Filip and Lacey, Cedric G and Baugh, Carlton M (2021) 'Statistics of galaxy mergers: bridging the gap between theory and observation.', Monthly Notices of the Royal Astronomical Society, 509 (4). pp. 5918-5937.

Abstract

We present a study of galaxy mergers up to z = 10 using the Planck Millennium cosmological dark matter simulation and the GALFORM semi-analytical model of galaxy formation. Utilizing the full 800 Mpc3 volume of the simulation, we studied the statistics of galaxy mergers in terms of merger rates and close pair fractions. We predict that merger rates begin to drop rapidly for high-mass galaxies (M* > 1011.3–1010.5 M⊙ for z = 0–4), as a result of the exponential decline in the galaxy stellar mass function. The predicted merger rates for massive galaxies (M* > 1010 M⊙) increase and then turn over with increasing redshift, by z = 3.5, in disagreement with hydrodynamical simulations and semi-empirical models. In agreement with most other models and observations, we find that close pair fractions flatten or turn over at some redshift (dependent on the mass selection). We conduct an extensive comparison of close pair fractions, and highlight inconsistencies among models, but also between different observations. We provide a fitting formula for the major merger time-scale for close galaxy pairs, in which the slope of the stellar mass dependence is redshift dependent. This is in disagreement with previous theoretical results that implied a constant slope. Instead, we find a weak redshift dependence only for massive galaxies (M* > 1010 M⊙): in this case the merger time-scale varies approximately as M−0.55∗⁠. We find that close pair fractions and merger time-scales depend on the maximum projected separation as r1.32max⁠, in agreement with observations of small-scale clustering of galaxies.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1093/mnras/stab3324
Publisher statement:This article has been accepted for publication in Monthly notices of the Royal Astronomical Society. ©: 2021 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:15 November 2021
Date deposited:25 May 2022
Date of first online publication:23 November 2021
Date first made open access:25 May 2022

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