Gaia-ESO Survey: Gas dynamics in the Carina Nebula through optical emission lines

TL;DR

This study uses Gaia-ESO Survey data to analyze gas dynamics in the Carina Nebula, revealing complex shell-like structures, varying ionization, and high-velocity gas components, advancing understanding of nebular kinematics and morphology.

Contribution

It provides a detailed analysis of nebular gas kinematics and structures in Carina, highlighting the presence of non-spherical shells and their interactions, which was not previously characterized in such detail.

Findings

Multiple shell-like expanding regions identified around key stars.

Gas temperatures and densities derived from emission line ratios.

High-velocity gas components linked to dust reflection of η Car spectrum.

Abstract

We present observations from the Gaia-ESO Survey in the lines of H$\alpha$, [N II], [S II] and He I of nebular emission in the central part of the Carina Nebula. We investigate the properties of the two already known kinematic components (approaching and receding, respectively), which account for the bulk of emission. Moreover, we investigate the features of the much less known low-intensity high-velocity (absolute RV $>$50 km/s) gas emission. We show that gas giving rise to H$\alpha$ and He I emission is dynamically well correlated, but not identical, to gas seen through forbidden-line emission. Gas temperatures are derived from line-width ratios, and densities from [S II] doublet ratios. The spatial variation of N ionization is also studied, and found to differ between the approaching and receding components. The main result is that the bulk of the emission lines in the central part of Carina arises from several distinct shell-like expanding regions, the most evident found around $\eta$ Car, the Trumpler 14 core, and the star WR25. Such "shells" are non-spherical, and show distortions probably caused by collisions with other shells or colder, higher-density gas. Part of them is also obscured by foreground dust lanes, while only very little dust is found in their interior. Preferential directions, parallel to the dark dust lanes, are found in the shell geometries and physical properties, probably related to strong density gradients in the studied region. We also find evidence that the ionizing flux emerging from $\eta$ Car and the surrounding Homunculus nebula varies with polar angle. The high-velocity components in the wings of H$\alpha$ are found to arise from expanding dust reflecting the $\eta$ Car spectrum.