The A2667 Giant Arc at z = 1.03: Evidence for Large-Scale Shocks at High Redshift

Abstract

We present the spatially resolved emission line ratio properties of a ~10¹⁰ M _⊙ star-forming galaxy at redshift z = 1.03. This galaxy is gravitationally lensed as a triple-image giant arc behind the massive lensing cluster A2667. The main image of the galaxy has magnification factors of 14 ± 2.1 in flux and ~2 × 7 in area, yielding an intrinsic spatial resolution of 115-405 pc after adaptive optics correction with OSIRIS at KECK II. The Hubble Space Telescope morphology shows a clumpy structure and the Hα kinematics indicates a large velocity dispersion with V _max sin (i)/σ ~ 0.73, consistent with high-redshift disk galaxies of similar masses. From the [N II]/Hα line ratios, we find that the central 350 pc of the galaxy is dominated by star formation. The [N II]/Hα line ratios are higher in the outer disk than in the central regions. Most noticeably, we find a blueshifted region of strong [N II]/Hα emission in the outer disk. Applying our recent H II region and slow-shock models, we propose that this elevated [N II]/Hα ratio region is contaminated by a significant fraction of shock excitation due to galactic outflows. Our analysis suggests that shocked regions may mimic flat or inverted metallicity gradients at high redshift.