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Dark Matter Halo Mergers: Dependence on Environment

Hester, J. A. and Tasitsiomi, A. (2010) Dark Matter Halo Mergers: Dependence on Environment. Astrophysical Journal, 715 (1). pp. 342-354. ISSN 0004-637X.

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This paper presents a study of the specific major merger rate as a function of group membership, local environment, and redshift in a very large, 500 h^(–1) Mpc, cosmological N-body simulation, the Millennium Simulation. The goal is to provide environmental diagnostics of major merger populations in order to test simulations against observations and provide further constraints on major merger driven galaxy evolution scenarios. A halo sample is defined using the maximum circular velocity, which is both well defined for subhalos and closely correlated with galaxy luminosity. Subhalos, including the precursors of major mergers, are severely tidally stripped. Major mergers between subhalos are therefore rare compared to mergers between subhalos and their host halos. Tidal stripping also suppresses dynamical friction, resulting in long major merger timescales when the more massive merger progenitor does not host other subhalos. When other subhalos are present, however, major merger timescales are several times shorter. This enhancement may be due to inelastic unbound collisions between subhalos, which deplete their orbital angular momentum and lead to faster orbital decay. Following these results, we predict that major mergers in group environments are dominated by mergers involving the central galaxy, that the specific major merger rate is suppressed in groups when all group members are considered together, and that the frequency of fainter companions is enhanced for major mergers and their remnants. We also measure an "assembly bias" in the specific major merger rate in that major mergers of galaxy-like halos are slightly suppressed in overdense environments while major mergers of group-like halos are slightly enhanced. A dynamical explanation for this trend is advanced which calls on both tidal effects and interactions between bound halos beyond the virial radii of locally dynamically dominant halos.

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Additional Information:© 2010 The American Astronomical Society. Received 2008 September 16; accepted 2010 April 4; published 2010 April 28. This work was partially funded by NSF grant 0707731 and NASA ATP grant NNX08AH30G. The authors thank E. Scannapieco for useful discussions and G. A. Mamon for useful comments on an earlier version of this paper. J.A.H. thanks S. Malhaotra, J. Rhoads, and the Arizona State University School of Earth and Space Exploration for their hospitality while this work was being completed. The Millennium Simulation databases used in this paper and the Web application providing online access to them were constructed as part of the activities of the German Astrophysical Virtual Observatory. The particular structure of the database design which allows efficient querying for merger trees is described in Lemson & Springel (2006).
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Subject Keywords:galaxies: evolution – galaxies: halos – galaxies: interactions
Issue or Number:1
Classification Code:PACS: 98.65.Fz; 98.62.Ai; 98.62.Gq; 95.35.+d.
Record Number:CaltechAUTHORS:20100526-131314127
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Official Citation: J. A. Hester and A. Tasitsiomi 2010 ApJ 715 342 doi: 10.1088/0004-637X/715/1/342
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:18460
Deposited By: Tony Diaz
Deposited On:03 Jun 2010 21:40
Last Modified:03 Oct 2019 01:42

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