The Kiloparsec-Scale Kinematics of High-Redshift Star-Forming Galaxies

摘要

We present the results of a spectroscopic survey of the kinematic structureof star-forming galaxies at redshift z ~ 2 - 3 using Keck/OSIRIS integral fieldspectroscopy. Our sample is comprised of 12 galaxies between redshifts z ~ 2.0and 2.5 and one galaxy at z ~ 3.3 which are well detected in either HAlpha or[O III] emission. These observations were obtained in conjunction with the Kecklaser guide star adaptive optics system, with a typical angular resolutionafter spatial smoothing ~ 0.15" (approximately 1 kpc at the redshift of thetarget sample). At most five of these 13 galaxies have spatially resolvedvelocity gradients consistent with rotation while the remaining galaxies haverelatively featureless or irregular velocity fields. All of our galaxies showlocal velocity dispersions ~ 60 - 100 km/s, suggesting that (particularly forthose galaxies with featureless velocity fields) rotation about a preferredaxis may not be the dominant mechanism of physical support. While some galaxiesshow evidence for major mergers such evidence is unrelated to the kinematics ofindividual components (one of our strongest merger candidates also exhibitsunambiguous rotational structure), refuting a simple bimodal disk/mergerclassification scheme. We discuss these data in light of complementary surveysand extant UV-IR spectroscopy and photometry, concluding that the dynamicalimportance of cold gas may be the primary factor governing the observedkinematics of z ~ 2 galaxies. We conclude by speculating on the importance ofmechanisms for accreting low angular-momentum gas and the early formation ofquasi-spheroidal systems in the young universe.(abridged)