Kinematics of Extremely Metal-poor Galaxies: Evidence for Stellar Feedback

TL;DR

This study investigates the kinematic behavior of ionized gas in extremely metal-poor galaxies, revealing feedback-driven outflows likely caused by supernovae, which may lead to gas escape from the galaxy.

Contribution

It provides new insights into the gas dynamics and feedback processes in XMP galaxies, highlighting the role of supernovae in driving outflows and influencing galaxy evolution.

Findings

Most XMPs have low rotation velocities (~tens of km/s)

Faint emission features indicate expanding shell-like structures with high mass loading factors

Gas outflows may escape the galaxy due to high expansion velocities

Abstract

The extremely metal-poor (XMP) galaxies analyzed in a previous paper have large star-forming regions with a metallicity lower than the rest of the galaxy. Such a chemical inhomogeneity reveals the external origin of the metal-poor gas fueling star formation, possibly indicating accretion from the cosmic web. This paper studies the kinematic properties of the ionized gas in these galaxies. Most XMPs have rotation velocity around a few tens of km/s. The star-forming regions appear to move coherently. The velocity is constant within each region, and the velocity dispersion sometimes increases within the star-forming clump towards the galaxy midpoint, suggesting inspiral motion toward the galaxy center. Other regions present a local maximum in velocity dispersion at their center, suggesting a moderate global expansion. The Halpha line wings show a number of faint emission features with amplitudes around a few percent of the main Halpha component, and wavelength shifts between 100 and 400 km/s. The components are often paired, so that red and blue emission features with similar amplitudes and shifts appear simultaneously. Assuming the faint emission to be produced by expanding shell-like structures, the inferred mass loading factor (mass loss rate divided by star formation rate) exceeds 10. Since the expansion velocity exceeds by far the rotational and turbulent velocities, the gas may eventually escape from the galaxy disk. The observed motions involve energies consistent with the kinetic energy released by individual core-collapse supernovae. Alternative explanations for the faint emission have been considered and discarded.