Far-Ultraviolet Observations of Starburst Galaxies with FUSE: Galactic Feedback in the Local Universe

TL;DR

This study analyzes far-ultraviolet spectra of 16 local starburst galaxies, revealing starburst-driven outflows, coronal gas cooling, and low escape fractions of ionizing radiation, providing insights into galactic feedback processes.

Contribution

First comprehensive FUSE UV spectral analysis of local starbursts linking outflows, coronal gas, and ionizing photon escape, enhancing understanding of feedback mechanisms.

Findings

Galactic outflows are common and increase with star formation rate.

Coronal-phase gas is detected in nearly all galaxies, indicating cooling at hot-cool gas interfaces.

Escape fraction of ionizing radiation is generally less than a few percent.

Abstract

We have analysed FUSE far-UV spectra of a sample of 16 local starbursts. These galaxies span ranges of almost three orders-of-magnitude in star formation rate and over two orders-of-magnitude in stellar mass. We find that the strongest interstellar absorption-lines are generally blueshifted relative to the galaxy systemic velocity by ~50 to 300 km/s, implying the presence of starburst-driven galactic outflows. The outflow velocites increase on-average with the star formation rate and the star formation rate per unit mass. We find that outflowing coronal-phase (T ~ several hundred thousand K) gas detected via the OVI 1032 absorption line in nearly every galaxy. The kinematics of this outflowing gas differs from the lower-ionization material, and agrees with predictions for radiatively cooling gas (most likely created at the interface between the hot outrushing gas traced by X-rays and cool ambient material). Emission from the coronal gas is not generally detected, implying that radiative cooling by this phase is not affecting the dynamics/energetics of the wind. We find that the weaker interstellar absorption lines lie close to the systemic velocity, implying that the outflowing gas has a lower column density than the quiescent gas in the starburst. From direct observation below the Lyman edge and from the small residual intensity at the core of the CII 1036 line, we conclude that the absolute escape fraction of ionizing radiation is small (typically less than a few percent). This sample provides a unique window on the global properties of local starburst galaxies and a useful comparison sample for understanding spectra of high redshift galaxies.