2011ApJ...732L..14Y

We present the first metallicity gradient measurement for a grand-design face-on spiral galaxy at z ∼ 1.5. This galaxy has been magnified by a factor of 22x by a massive, X-ray luminous galaxy cluster MACS J1149.5+2223 at z = 0.544. Using the Laser Guide Star Adaptive Optics aided integral field spectrograph OSIRIS on KECK II, we target the Hα emission and achieve a spatial resolution of 0".1, corresponding to a source-plane resolution of 170 pc. The galaxy has well-developed spiral arms and the nebular emission line dynamics clearly indicate a rotationally supported disk with V_rot/σ ∼ 4. The best-fit disk velocity field model yields a maximum rotation of V_rot sin i = 150±15 km/s, and a dynamical mass of M_dyn= (1.3 ±0.2)x10¹⁰ cosec²(i) M_☉(within 2.5 kpc), where the inclination angle i = 45°±10°. Based on the [N II] and Hα ratios, we measured the radial chemical abundance gradient from the inner hundreds of parsecs out to ∼5 kpc. The slope of the gradient is -0.16±0.02 dex/kpc, significantly steeper than the gradient of late-type or early-type galaxies in the local universe. If representative of disk galaxies at z ∼ 1.5, our results support an "inside-out" disk formation scenario in which early infall/collapse in the galaxy center builds a chemically enriched nucleus, followed by slow enrichment of the disk over the next 9 Gyr.