Journal Article

The effect of gas fraction on the morphology and time-scales of disc galaxy mergers

Jennifer M. Lotz, Patrik Jonsson, T. J. Cox and Joel R. Primack

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 404, issue 2, pages 590-603
Published in print May 2010 | ISSN: 0035-8711
Published online May 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.16269.x
The effect of gas fraction on the morphology and time-scales of disc galaxy mergers

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Gas-rich galaxy mergers are more easily identified by their disturbed morphologies than mergers with less gas. Because the typical gas fraction of galaxy mergers is expected to increase with redshift, the under-counting of low gas-fraction mergers may bias morphological estimates of the evolution of galaxy merger rate. To understand the magnitude of this bias, we explore the effect of gas fraction on the morphologies of a series of simulated disc galaxy mergers. With the resulting g-band images, we determine how the time-scale for identifying major and minor galaxy mergers via close projected pairs and quantitative morphology (the Gini coefficient G, the second-order moment of the brightest 20 per cent of the light M20 and asymmetry A) depends on baryonic gas fraction fgas. Strong asymmetries last significantly longer in high gas-fraction mergers of all mass ratios, with time-scales ranging from ≤300 Myr for fgas∼ 20 per cent to ≥1 Gyr for fgas∼ 50 per cent. Therefore, the strong evolution with redshift observed in the fraction of asymmetric galaxies may reflect evolution in the gas properties of galaxies rather than the global galaxy merger rate. On the other hand, the time-scale for identifying a galaxy merger via GM20 is weakly dependent on gas fraction (∼200–400 Myr), consistent with the weak evolution observed for GM20 mergers.

Keywords: galaxies: evolution; galaxies: interactions; galaxies: structure

Journal Article.  8373 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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