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Published June 1, 2009 | Published
Journal Article Open

The Kiloparsec-scale Kinematics of High-redshift Star-forming Galaxies

Abstract

We present the results of a spectroscopic survey of the kinematic structure of star-forming galaxies at redshift z ~ 2-3 using Keck/OSIRIS integral field spectroscopy. Our sample is comprised of 12 galaxies between redshifts z ~ 2.0 and 2.5 and one galaxy at z ~ 3.3 which are well detected in either Hα or [O III] emission. These galaxies are generally representative of the mean stellar mass of star-forming galaxies at similar redshifts, although they tend to have star formation rate surface densities slightly higher than the mean. These observations were obtained in conjunction with the Keck laser guide star adaptive optics system, with a typical angular resolution after spatial smoothing ~0".15 (approximately 1 kpc at the redshift of the target sample). At most five of these 13 galaxies have spatially resolved velocity gradients consistent with rotation while the remaining galaxies have relatively featureless or irregular velocity fields. All of our galaxies show local velocity dispersions ~60-100 km s^(–1), suggesting that (particularly for those galaxies with featureless velocity fields) rotation about a preferred axis may not be the dominant mechanism of physical support. While some galaxies show evidence for major mergers such evidence is unrelated to the kinematics of individual components (one of our strongest merger candidates also exhibits unambiguous rotational structure), refuting a simple bimodal disk/merger classification scheme. We discuss these data in light of complementary surveys and extant UV-IR spectroscopy and photometry, concluding that the dynamical importance of cold gas may be the primary factor governing the observed kinematics of z ~ 2 galaxies. We conclude by speculating on the importance of mechanisms for accreting low angular momentum gas and the early formation of quasi-spheroidal systems in the young universe.

Additional Information

© 2009 The American Astronomical Society. Received 2009 January 19; accepted 2009 March 27; published 2009 May 18. The authors thank Randy Campbell, Al Conrad, and Jim Lyke for their invaluable assistance obtaining the observations presented herein. D.R.L. also thanks Andrew Benson and Mark Swinbank for constructive discussions, Naveen Reddy for providing stellar mass function data, and the anonymous referee for helpful suggestions which improved the final draft of this manuscript. D.R.L. and C.C.S. have been supported by grants AST-0606912 and AST-0307263 from the US National Science Foundation. Additional support for this work was provided by NASA through Hubble Fellowship grant HF-01221.01 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. Finally, we wish to extend thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests.

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August 21, 2023
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