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Merger Signatures in the Dynamics of Star-forming Gas

Hung, Chao-Ling and Hayward, Christopher C. and Smith, Howard A. and Ashby, Matthew L. N. and Lanz, Lauranne and Martínez-Galarza, Juan R. and Sanders, D. B. and Zezas, Andreas (2016) Merger Signatures in the Dynamics of Star-forming Gas. Astrophysical Journal, 816 (2). Art. No. 99. ISSN 0004-637X.

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The recent advent of integral field spectrographs and millimeter interferometers has revealed the internal dynamics of many hundreds of star-forming galaxies. Spatially resolved kinematics have been used to determine the dynamical status of star-forming galaxies with ambiguous morphologies, and constrain the importance of galaxy interactions during the assembly of galaxies. However, measuring the importance of interactions or galaxy merger rates requires knowledge of the systematics in kinematic diagnostics and the visible time with merger indicators. We analyze the dynamics of star-forming gas in a set of binary merger hydrodynamic simulations with stellar mass ratios of 1:1 and 1:4. We find that the evolution of kinematic asymmetries traced by star-forming gas mirrors morphological asymmetries derived from mock optical images, in which both merger indicators show the largest deviation from isolated disks during strong interaction phases. Based on a series of simulations with various initial disk orientations, orbital parameters, gas fractions, and mass ratios, we find that the merger signatures are visible for ~0.2–0.4 Gyr with kinematic merger indicators but can be approximately twice as long for equal-mass mergers of massive gas-rich disk galaxies designed to be analogs of z ~ 2–3 submillimeter galaxies. Merger signatures are most apparent after the second passage and before the black holes coalescence, but in some cases they persist up to several hundred Myr after coalescence. About 20%–60% of the simulated galaxies are not identified as mergers during the strong interaction phase, implying that galaxies undergoing violent merging process do not necessarily exhibit highly asymmetric kinematics in their star-forming gas. The lack of identifiable merger signatures in this population can lead to an underestimation of merger abundances in star-forming galaxies, and including them in samples of star-forming disks may bias the measurements of disk properties such as intrinsic velocity dispersion.

Item Type:Article
Related URLs:
URLURL TypeDescription
Hung, Chao-Ling0000-0002-6879-3639
Hayward, Christopher C.0000-0003-4073-3236
Ashby, Matthew L. N.0000-0002-3993-0745
Lanz, Lauranne0000-0002-3249-8224
Martínez-Galarza, Juan R.0000-0002-5069-0324
Sanders, D. B.0000-0002-1233-9998
Zezas, Andreas0000-0001-8952-676X
Additional Information:© 2016. The American Astronomical Society. Received 2015 August 16; accepted 2015 November 19; published 2016 January 14. C.-L.H., H.A.S., M.L.N.A., and J.R.M.-G. wish to acknowledge partial funding support from NASA grants NNX14AJ61G and NNX15AE56G. C.C.H. is grateful to the Gordon and Betty Moore Foundation for financial support. The computations in this paper were run on the Odyssey cluster supported by the FAS Division of Science, Research Computing Group at Harvard University.
Group:TAPIR, Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Gordon and Betty Moore FoundationUNSPECIFIED
Harvard UniversityUNSPECIFIED
Subject Keywords:galaxies: interactions; galaxies: kinematics and dynamics; galaxies: structure
Issue or Number:2
Record Number:CaltechAUTHORS:20160205-112349566
Persistent URL:
Official Citation:Chao-Ling Hung (洪肇伶) et al 2016 ApJ 816 99
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:64271
Deposited By: George Porter
Deposited On:08 Feb 2016 18:41
Last Modified:09 Mar 2020 13:19

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