UV Cooling via O VI Emission in the Superwind of M82 Observed with the Far Ultraviolet Spectroscopic Explorer (FUSE)

Abstract

We examined archival Far Ultraviolet Spectroscopic Explorer data to search for far-ultraviolet emission lines in the starburst galaxy M82. The observations were made in an outflow region that extends beyond the galactic disk. We found the O vi λ λ 1032, 1038 emission lines from the galaxy’s southern outflow region. The O vi lines suggest that the outflowing warm-hot gas is undergoing radiative cooling. We measured a radial velocity of ∼420 km s ^−1 from the O vi lines, which is faster than the velocity seen in H α observations. The O vi λ 1038 emission line seems to be blended with the C ii λ 1037 emission line, which has a radial velocity of ∼300 km s ^−1 , similar to what is observed in H α observations. The outflow medium of M82 appears to be composed of gas in multiple phases with varying temperatures and kinematics. Future spectroscopic observations in high energy regimes covering a wider spatial area are necessary to understand better the properties of the warm-hot gas medium in the outflow.

Keywords

• Ultraviolet spectroscopy
• Galaxies
• Starburst galaxies
• Circumgalactic medium
• Extragalactic astronomy