METALLICITY GRADIENT OF A LENSED FACE-ON SPIRAL GALAXY AT REDSHIFT 1.49

We present the first metallicity gradient measurement for a grand-design face-on spiral galaxy at z similar to 1.5. This galaxy has been magnified by a factor of 22 x 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 Ha 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/sigma similar to 4. The best-fit disk velocity field model yields a maximum rotation of V-rot sin i = 150 +/- 15 km s(-1), and a dynamical mass of M-dyn = (1.3 +/- 0.2) x 10(10) cosec(2)(i) M-circle dot (within 2.5 kpc), where the inclination angle i = 45 degrees +/- 10 degrees. Based on the [N II] and II alpha ratios, we measured the radial chemical abundance gradient from the inner hundreds of parsecs out to similar to 5 kpc. The slope of the gradient is -0.16 +/- 0.02 dex kpc(-1), significantly steeper than the gradient of late-type or early-type galaxies in the local universe. If representative of disk galaxies at z similar to 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 9Gyr.