The physical nature of the 8 o'clock arc based on near-IR IFU spectroscopy with SINFONI

TL;DR

This study uses near-IR IFU spectroscopy and lens modeling to analyze the complex kinematics and physical conditions of the gravitationally lensed 8 o'clock arc galaxy, revealing outflows and higher gas densities compared to local counterparts.

Contribution

It provides a detailed spatially-resolved analysis of the 8 o'clock arc, demonstrating the galaxy's complex velocity field and physical properties through advanced lens modeling and spectroscopy.

Findings

The galaxy exhibits a complex velocity field not explained by a single disk.

Detection of gas outflows with velocities around 200 km/s.

Higher gas surface density and electron density than similar local galaxies.

Abstract

We present an analysis of near-infrared integral field unit spectroscopy of the 8 o'clock arc, a gravitationally lensed Lyman break galaxy, taken with SINFONI. We explore the shape of the spatially-resolved H\beta\ profile and demonstrate that we can decompose it into three components that partially overlap (spatially) but are distinguishable when we include dynamical information. We use existing B and H imaging from the Hubble Space Telescope to construct a rigorous lens model using a Bayesian grid based lens modelling technique. We apply this lens model to the SINFONI data cube to construct the de-lensed H\beta\ line-flux velocity and velocity dispersion maps of the galaxy. We find that the 8 o'clock arc has a complex velocity field that is not simply explained by a single rotating disk. The H\beta\ profile of the galaxy shows a blue-shifted wing suggesting gas outflows of ~ 200 km s^{-1}. We confirm that the 8 o'clock arc lies on the stellar mass--oxygen abundance--SFR plane found locally, but it has nevertheless significantly different gas surface density (a factor of 2--4 higher) and electron density in the ionized gas (five times higher) from those in similar nearby galaxies, possibly indicating a higher density interstellar medium for this galaxy.