Ionized Gas Kinematics with FRESCO: An Extended, Massive, Rapidly Rotating Galaxy at z=5.4

With the remarkable sensitivity and resolution of JWST in the infrared, measuring rest-optical kinematics of galaxies at z > 5 has become possible for the first time. This study pilots a new method for measuring galaxy dynamics for highly multiplexed, unbiased samples by combining FRESCO NIRCam grism spectroscopy and JADES medium-band imaging. Here we present one of the first JWST kinematic measurements for a galaxy at z > 5. We find a significant velocity gradient, which, if interpreted as rotation, yields V-rot = 305 +/- 70 km s(-1), and we hence refer to this galaxy as Twister-z5. With a rest-frame optical effective radius of r(e) = 2.25 kpc, the high rotation velocity in this galaxy is not due to a compact size, as may be expected in the early Universe, but rather to a high total mass, log(M-dyn/M-circle dot) = 11.2 +/- 0.2. This is a factor of roughly 10x higher than the stellar mass within r(e). We also observe that the radial H alpha equivalent width profile and the specific star formation rate map from resolved stellar population modeling are centrally depressed by a factor of similar to 1.5 from the center to r(e). Combined with the morphology of the line-emitting gas in comparison to the continuum, this centrally suppressed star formation is consistent with a star-forming disk surrounding a bulge growing inside out. While large, rapidly rotating disks are common to z similar to 2, the existence of one after only 1 Gyr of cosmic time, shown for the first time in ionized gas, adds to the growing evidence that some galaxies matured earlier than expected in the history of the Universe.