THE HYDRODYNAMIC EFFECTS OF NUCLEAR ACTIVE GALAXY WINDS ON HOST GALAXIES.

Abstract

In order to test the hypothesized existence of a powerful, thermal wind in active galactic nuclei, the hydrodynamic effects of such a wind on a model galactic interstellar medium (ISM) are investigated. The properties of several model ISMs are derived from observations of the Milky Way's ISM and those of nearby spiral and elliptical galaxies. The wind is assumed to be highly supersonic with spherical symmetry and constant mechanical luminosity, L(W). The propagation of the wind into the low density gas component of the ISM is studied using the Kompaneets approximation of a strong explosion in an exponential atmosphere. Flattened gas distributions are shown to experience "blow-out" of wind gas along the symmetry axis. The results show that for typical ISM gas pressures ( < 10⁻¹¹ ergs cm⁻³), the extent of the wind can range from 1 to 10 kpc for wind luminosities of 10⁴² to 10⁴⁶ ergs sec⁻¹ in a timescale of less than 10⁷ years. The steady state wind flow pattern and an estimate of the timescale required to reach a quasi-steady state are also determined. Next, the interaction of dense, interstellar clouds with the wind is investigated. The stability and mass loss of clouds in the wind are studied and it is proposed that clouds survive the encounter with the wind over large timescales ( >10⁷ yrs.). The physical structure and motion of the clouds are calculated, showing that large clouds (10³ solar masses) can be accelerated to velocities in excess of the galactic escape velocity. Finally, it is proposed that the Narrow Emission Line Regions (NELR) of active galaxies are the result of the interaction of active nuclei photons and a thermal wind on large, interstellar clouds. The physical state of the NELR is re-examined and shown to be compatible with this hypothesis. Arguments are presented to show that the NELR clouds must be massive and unable to be accelerated to NELR velocities by photon momentum alone. A Monte Carlo-type calculation is made to determine Narrow Emission Line profiles from an ensemble of photoionized interstellar clouds in the wind. These theoretical line profiles are shown to agree reasonably well with observed line profiles.