The nuclear superbubble of NGC 3079

We have used the Hawaii Imaging Fabry-Perot Interferometer (HIFI) at the CFH 3.6 m telescope to map Hα + [N II] λλ6548, 6583 emission-line profiles across the entire edge-on, nearby SBc galaxy NGC 3079, with resolution 70 km s-1 and subarsecond sampling. Blue and red long-slit spectra were obtained with the Double Spectrograph on the Palomar 5 meter telescope to provide additional emission-line diagnostics. A spectacular, line emitting bubble of diameter 13″ (∼1.1 kpc) is observed immediately east of the nucleus. Its unusual gaseous excitation (e.g., [N II] λ6583/Hα > 1) suggests that shocks are important. Extremely violent gas motions that range over 2000 km s-1 are detected across the bubble and diametrically opposite on the west side of the nucleus. Nonrotational motions are also found in the inner galaxy disk. The complete spatial and spectral sampling of the emission-line profiles allows us to constrain the general flow pattern of the gas in the line-emitting bubble. An ovoidal bubble, inflated from the nucleus with monotonically increasing velocities (V ∝ Rn with 2 < n < 3) and inclined ∼3° from the plane of the sky, provides a good first-order fit to its velocity field. A total ionized mass and kinetic energy of ∼1 × 107/Ne M⊙ and ∼2 × 1056/Ne ergs, respectively, are involved in this outflow. Although the [S II] density in the bubble is only weakly constrained, we find no convincing evidence anywhere in the bubble (even near the nucleus) for the [S II] density to be above the low-density limit (Ne ≈ 125 cm-3). The radial density gradient previously reported in this galaxy is not confirmed, so the [S II] density profile cannot be used to find the size of the energy injection zone in this object. The Balmer decrements in the nucleus and the brighter regions of the outflow show a steep decrease in reddening away from the galaxy plane. The outflow mass is similar to, but the kinetic energy may be 10 times larger than, the superwinds in the Seyfert galaxy NGC 1068 and the starburst galaxy M82. Therefore, the superbubble of NGC 3079 is the most powerful example known of a windblown bubble, and an excellent laboratory to study wind dynamics. The dimensions and energies of the bubble imply that it is likely to be in the blowout phase and partially ruptured. The predicted rate of kinetic energy output from the central starburst appears sufficient to power most of this outflow. It is possible that a central active galactic nucleus also contributes to the outflow.