A nuclear, disk-focused wind and the bipolar structure of the spiral galaxy NGC 3079

Abstract

Multiconfiguration, VLA radio continuum images of the edge-on spiral galaxy NGC 3079 are presented at a resolution of ~1". An extraordinary "figure eight" structure is found aligned along the minor axis of the galaxy, centered on the nucleus, and extending 3 kpc above and below the plane. The geometry of the structure, the evidence for unusually high nuclear gas velocities and the properties of the radio emission suggest that a wind-type flow is taking place, away from the nucleus. The mass-loss rate, velocity, and mechanical energy of the wind are determined by fitting model visibility curves, as derived from hydrodynamic wind calculations, to the observed visibility curves of the nuclear region. Analysis of the interaction of such a wind with the ambient disk and halo gas reveals that the disk "focuses" the initially spherical wind so that the material it ploughs up forms a figure eight pattern. The resulting pattern is found to agree exactly with the geometry of the thermal gas as traced by Hα emission. The results of the model suggest that 2.0 x 10^6^ years have elapsed since the wind last turned on.