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Session 24 - Seyfert & Starburst Galaxies; Winds, Outflows & Energetics.
Oral session, Monday, January 15
Corte Real, Hilton
We present detailed spectroscopic and multiband photometric observations of the nearby galaxy M82 in order to study the high-velocity outflows observed in such galaxies as a property of the energetic starburst phenomena associated with their nuclei. The high spatial and kinematic resolution of our Fabry-Perot observations has allowed us to perform photometric analysis of \ha, \nii, and øiii\ spectral lines at roughly one hundred thousand positions across the extent of the galaxy.
The observed velocities of the \ha-emitting gas in M82 suggest a bipolar outflow of material along the minor axis at a projected velocity of \sim300 \kms, fueled by the bright nuclear starburst regions in the galaxy's disk. All three spectral lines show double components in the centers of the outflowing lobes, with the \ha\ line split by \sim300 \kms\ over a region almost a kiloparsec in size. We argue for a model in which the optical emission is radiated by denser ambient material on the surface of ``bubbles'' that have been evacuated by a hot wind (\sim10^8 K) visible at x-ray wavelengths. The outflow is confined to a cylinder within 350 pc of the disk, but flares outward in a cone beyond that point. The optical line-emitting filaments consist of both gas that has been entrained from the disk by the outflow and material already present in the halo of M82.
Line ratio maps and published observations at infrared and x-ray wavelengths have been used to investigate the excitation mechanisms operating in the disk and outflow of the galaxy. The strong spatial correlation between ROSAT HRI and our \ha\ emission maps indicates a unified source for the extensive x-ray halo and optical filaments, presumably originating in shocks at the outflow interface. However, the optical emission line ratio maps suggest a stronger role for photoionization than previously thought, particularly close to the starburst nucleus. There are also indications of a limited diffuse ionized medium (DIM) in the disk of M82, similar to that seen in NGC 891 and other star forming galaxies, as well as an extensive dusty halo.
This research was supported by generous grants from Sigma Xi, the Texas Space Grant Consortium, and the Dean of Natural Sciences at Rice University, Houston, Texas.
