THE KILOPARSEC-SCALE KINEMATICS OF HIGH-REDSHIFT STAR-FORMING GALAXIES

We present the results of a spectroscopic survey of the kinematic structure of star-forming galaxies at redshift z similar to 2-3 using Keck/OSIRIS integral field spectroscopy. Our sample is comprised of 12 galaxies between redshifts z similar to 2.0 and 2.5 and one galaxy at z similar to 3.3 which are well detected in either H alpha 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 similar to 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 similar to 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 similar to 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.