Close pairs of galaxies and merger rate evolution
Date
2017-11-27
Authors
Patton, David Robert
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Abstract
New techniques are developed for relating the statistics of close galaxy pairs to the galaxy merger and accretion rates. Unlike the traditional pair fraction approach, these methods are shown to be robust to a number of selection effects related to the depth and completeness of the sample. These techniques are applied to the large, well-defined SSRS2 (z ∼ 0) and CNOC2 (0.1 ≤ ± ≤ 0.55) redshift surveys, yielding the first secure measurements of close pair statistics at low and moderate redshift. These results imply that the galaxy merger and accretion rates increase with redshift, approximately as (1 + z)2±1.5, for galaxies brighter than MB = –18.
The CNOC2 survey is used to carry out a detailed comparison between close companions and field galaxies. Paired galaxies are found to be of slightly earlier spectral type, with a larger spread in properties. In particular, the spectral indices of close companions imply a more complex star formation history, as would be expected if galaxy interactions and mergers are prevalent.
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Red shift, Galaxies