Journal Article

Dry mergers: a crucial test for galaxy formation

S. Khochfar and J. Silk

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 397, issue 1, pages 506-510
Published in print July 2009 | ISSN: 0035-8711
Published online July 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.14958.x
Dry mergers: a crucial test for galaxy formation

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We investigate the role that dry mergers play in the build-up of massive galaxies within the cold dark matter paradigm. Implementing an empirical shut-off mass scale for star formation, we find a nearly constant dry merger rate of ∼6 × 10−5 Mpc−3 Gyr−1 at z≤ 1 and a steep decline at larger z. Less than half of these mergers are between two galaxies that are morphologically classified as early-types, and the other half is mostly between an early- and late-type galaxy. Latter are prime candidates for the origin of tidal features around red elliptical galaxies. The introduction of a transition mass scale for star formation has a strong impact on the evolution of galaxies, allowing them to grow above a characteristic mass scale of M*,c∼ 6.3 × 1010 M by mergers only. As a consequence of this transition, we find that around M*,c, the fraction of 1:1 mergers is enhanced with respect to unequal mass major mergers. This suggests that it is possible to detect the existence of a transition mass scale by measuring the relative contribution of equal mass mergers to unequal mass mergers as a function of galaxy mass. The evolution of the high-mass end of the luminosity function is mainly driven by dry mergers at low z. We however find that only 10–20 per cent of galaxies more massive than M*,c experience dry major mergers within their last Gyr at any given redshift z≤ 1.

Keywords: galaxies: evolution; galaxies: formation; galaxies: general; galaxies: interactions

Journal Article.  4065 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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