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 2Y3 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 1⁄4 2:1820, 2.0067, and 3.3172, respectively, each of which is well resolvedwith a PSF measuring approximately 0.1100Y0.1500 ( 900Y1200 pc at z 2Y3) after cosmetic smoothing. Neither galaxy at z 2 exhibits substantial kinematic structure on scales k30 km s ; both are instead consistent with largely dispersiondominated velocity fields with 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 4 kpc with peak-to-peak amplitude of 140 km s . It is unlikely that DSF 2237a-C2 represents a dynamically cold rotating disk of ionized gas as the local velocity dispersion of the galaxy ( 1⁄4 79 km s ) 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. Subject headinggs: galaxies: high-redshift — galaxies: kinematics and dynamics — galaxies: starburst