Abstract
We present the first metallicity gradient measurement for a grand-design
face-on spiral galaxy at z$\sim$1.5. This galaxy has been magnified by a factor
of 22$\times$ 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\farcs1, corresponding to a source plane resolution of
170 parsec. The galaxy has well-developed spiral arms and the nebular emission
line dynamics clearly indicate a rotationally supported disk with V$_rot$/
$\sigma$ $\sim$ 4. The best-fit disk velocity field model yields a maximum
rotation of V$_rot$$i$=150$\pm$15 km s$^-1$, and a dynamical
mass of
M$_dyn$=1.3$\pm0.2\times10^10$csc$^2$(i)\,M$_ødot$ (within
2.5\,kpc), where the inclination angle i=45$\pm10^\circ$. Based on the \nii\
and \ha\ ratios, we measured the radial chemical abundance gradient from the
inner hundreds of parsecs out to $\sim$5 kilo-parsecs. The slope of the
gradient is -0.16$\pm$0.02 dex kpc$^-1$, significantly steeper than the
gradient of late-type or early-type galaxies in the local universe. If
representative of disk galaxies at z$\sim$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 Gyrs.
Description
[1103.3277] Metallicity Gradient of a Lensed Face-on Spiral Galaxy at Redshift 1.49
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