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

TL;DR

This study uses gravitational lensing and adaptive optics to analyze a high-redshift galaxy, revealing evidence of large-scale shocks likely caused by galactic outflows, which can affect metallicity measurements.

Contribution

It provides spatially resolved emission line data of a z=1.03 galaxy, demonstrating shock excitation impacts on metallicity gradient interpretations at high redshift.

Findings

Detection of shock-excited regions in the galaxy

Elevated [NII]/Hα ratios indicating shocks

Shocks may mimic inverted metallicity gradients

Abstract

We present the spatially resolved emission line ratio properties of a ~10^10 M_sun star-forming galaxy at redshift z=1.03. This galaxy is gravitationally lensed as a triple-image giant arc behind the massive lensing cluster Abell 2667. The main image of the galaxy has magnification factors of 14+/-2.1 in flux and ~ 2 by 7 in area, yielding an intrinsic spatial resolution of 115-405 pc after AO correction with OSIRIS at KECK II. The HST morphology shows a clumpy structure and the H\alpha\ kinematics indicates a large velocity dispersion with V_{max} sin(i)/\sigma ~ 0.73, consistent with high redshift disk galaxies of similar masses. From the [NII]/H\alpha\ line ratios, we find that the central 350 parsec of the galaxy is dominated by star formation. The [NII]/H\alpha\ line ratios are higher in the outer-disk than in the central regions. Most noticeably, we find a blue-shifted region of strong [NII]/H\alpha\ emission in the outer disk. Applying our recent HII region and slow-shock models, we propose that this elevated [NII]/H\alpha\ 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.