Rotation on sub-kpc scales in the strongly lensed z~3 'arc&core' and implications for high-redshift galaxy dynamics

TL;DR

This study compares the internal kinematics of a strongly lensed galaxy at z=3.2 with unlensed galaxies, revealing potential observational biases in high-redshift galaxy dynamics studies due to target selection.

Contribution

It provides the first detailed comparison of sub-kiloparsec scale rotation in a strongly lensed z~3 galaxy with unlensed counterparts, highlighting biases in observational samples.

Findings

Lensed galaxy shows signs of rotation on sub-kpc scales.

Unlensed galaxies have higher ratios of random to bulk motion.

Selection bias towards bright targets may affect kinematic studies.

Abstract

Strongly lensed galaxies at high redshift provide a unique window into the early universe. We compare the internal kinematics of the strongly lensed Lyman-break galaxy (LBG) 'arc&core' at z=3.2 (the first strongly lensed z~3 LBG with the signs of rotation on sub-kiloparsec scales) with an LBG that is not gravitationally lensed, as well as with a larger sample of actively star-forming galaxies at slightly lower redshifts. All galaxies have deep rest-frame optical integral-field spectroscopy obtained with the VLT. The unlensed galaxies appear to have a larger ratio of random to bulk motion. Field galaxies also have broader lines than strongly lensed LBGs with rest-optical spectroscopy, where spectra were extracted from regions with similar physical size. To ensure observational success, studies of high-redshift galaxy kinematics often focus on bright and luminous targets, and our comparison suggests that this may lead to a serious bias.