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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
earth and planetary sciences
Galaxy merger statistics and inferred bulge-to-disk ratios in cosmological SPH simulations
Astrophysical Journal, Volume 647, No. 2 I, Year 2006
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Description
We construct merger trees for galaxies identified in a cosmological hydrodynamic simulation and use them to characterize predicted merger rates as a function of redshift, galaxy mass, and merger mass ratio. Atz = 0.3, we find a mean rate of 0.054 mergers per galaxy per Gyr above a 1:2 mass ratio threshold for massive galaxies (baryonic mass above 6.4 × 1010 M ⊙), but only 0.018 Gyr-1 for lower mass galaxies. The mass ratio distribution is prop;Rmerg-1.2 for the massive galaxy sample, so high-mass mergers dominate the total merger growth rate. The predicted rates increase rapidly with increasing redshift, and they agree reasonably well with observational estimates. A substantial fraction of galaxies do not experience any resolved mergers during the course of the simulation, and even for the high-mass sample, only 50% of galaxies experience a greater than 1:4 merger since z = 1. Typical galaxies thus have fairly quiescent merger histories. We assign bulge-to-disk ratios to simulated galaxies by assuming that mergers above a mass ratio threshold Rmajor convert stellar disks into spheroids. With Rmajor values of 1:4, we obtain a fairly good match to the observed dependence of the early-type fraction on galaxy mass. However, the predicted fraction of truly bulge-dominated systems (f bulge > 0.8) is small, and producing a substantial population of bulge-dominated galaxies may require a mechanism that shuts off gas accretion at late times and/or additional processes (besides major mergers) for producing bulges. © 2006. The American Astronomical Society. All rights reserved.
Authors & Co-Authors
Maller, Ariyeh H.
United States, New York
New York City College of Technology
Katz, Neal S.
United States, Amherst
University of Massachusetts Amherst
Keres̀, Dušan
United States, Amherst
University of Massachusetts Amherst
Dav́e, Romeel
United States, Tucson
The University of Arizona
Weinberg, David H.
United States, Columbus
The Ohio State University
Statistics
Citations: 121
Authors: 5
Affiliations: 4
Identifiers
Doi:
10.1086/503319
ISSN:
0004637X
Study Design
Cross Sectional Study