Integral field spectroscopy of high-redshift star-forming galaxies with laser-guided adaptive optics: Evidence for dispersion-dominated kinematics

We present early results from an ongoing study of the kinematic structure of star-forming galaxies at redshift z similar to 2-3 using integral-field spectroscopy of rest-frame optical nebular emission lines in combination with Keck laser guide star adaptive optics (LGSAO). We show kinematic maps of three target galaxies Q1623-BX453, Q0449-BX93, and DSF 2237a-C2 located at redshifts z = 2.1820, 2.0067, and 3.3172, respectively, each of which is well resolved with a PSF measuring approximately 0.11-0.15 (similar to 900-1200 pc at z similar to 2-3) after cosmetic smoothing. Neither galaxy at z similar to 2 exhibits substantial kinematic structure on scales greater than or similar to 30 km s(-1); both are instead consistent with largely dispersion-dominated velocity fields with sigma similar to 80 km s(-1) along any given line of sight into the galaxy. In contrast, DSF 2237a-C2 presents a well-resolved gradient in velocity over a distance of similar to 4 kpc with peak-to-peak amplitude of 140 km s(-1). It is unlikely that DSF 2237a-C2 represents a dynamically cold rotating disk of ionized gas as the local velocity dispersion of the galaxy (sigma = 79 km s(-1))is comparable to the observed shear. While some gas cooling models reproduce the observed kinematics better than a simple rotating disk model, even these provide a poor overall description of the target galaxies, suggesting that our current understanding of gas cooling mechanisms in galaxies in the early universe is (at best) incomplete.