Nuclear winds in active galaxies

The consequences of nuclear winds in active galaxies are investigated. Nuclear winds are defined to be any supersonic wind generated by the active nucleus; starburst winds could be similar. A review of theory and observation relevant to nuclear winds is presented, and the range of possible wind parameters is defined. A detailed analysis of the interaction of a nuclear wind with the hot interstellar medium (ISM) of a host elliptical galaxy is performed. The hot ISM in elliptical galaxies shortens the timescale of the interaction and generally prevents a dense, wind driven shell from forming. Nuclear winds will have a profound effect on the host galaxy, replacing some or all of the ISM. Nuclear winds can also shut off normal star formation in the galaxy as well as that due to cooling flows. The effect of mass loading of the nuclear wind by stellar wind mass loss is investigated. An ideal hydrodynamic analysis finds that stellar winds are unlikely to mass load the nuclear wind unless instabilities act very rapidly to mix the stellar wind material into the nuclear wind. Observational signatures of the nuclear wind are presented, the most striking of which is the alteration of the x-ray profile of the host galaxy. A powerful nuclear wind will eject the hot component of the ISM from its host galaxy, which will not show the extended x-ray halo normally seen in large elliptical galaxies. Instead, only the central nuclear and stellar x-ray sources will be seen. The shape of the radial ionization parameter profile is also a signature of the nuclear wind, and will indicate the presence of stellar wind mass loading. The relationship between the nuclear wind and emission-line clouds is discussed, including cloud properties and dynamics. The narrow-line clouds are capable of mass loading the nuclear wind and may be the source of the inferred ionization gradients. A stable zone may exist in the stellar core of the host galaxy. Emission-line clouds could survive in this zone for a comparatively long time. Finally, a parameter space for nuclear winds is presented. Nuclear winds are likely to be fast and at least moderately efficient.