Observations of molecular gas (through CO emission, for example) around pre-main sequence stars often reveal bi-polar outflows. Such data have been interpreted in terms of a dense shell of material which has been swept up by a strong stellar wind (e.g., Snell, Loren & Plambeck 1980). This interpretation implies a wide-angle gaseous outflow, in contrast to the narrow jets which are the topic of this conference. In this section, I describe evidence for wide-angle outflows in AGN and speculate on their possible relationship to jets.
The strongest evidence for such wide-angle outflows is found in the radio-quiet Seyfert galaxies. As already discussed, ionizing radiation escapes from the nuclei of a substantial fraction of Seyfert 2 galaxies in wide bi-cones. This radiation ionizes gas in the narrow line region and the larger scale "extended narrow line region" (Unger et al. 1987). In some galaxies, the extended narrow line region may comprise ambient gas kinematically undisturbed by the nucleus, but others exhibit peculiar motions indicative of a component of radial outflow within the ionization cone. Such conical outflows are best recognized in highly inclined Seyferts (where the outflowing gas is not confused by projection onto HII regions in the galaxy disk); good examples include NGC 5506 (Wilson, Baldwin & Ulvestad 1985), NGC 4388 (Corbin, Baldwin & Wilson 1988), and NGC 3281 (Storchi-Bergmann, Wilson & Baldwin 1992). All these galaxies exhibit double-peaked line profiles within the cones, a characteristic expected for radial outflow, even if the gas fully fills the cone. Other examples of disturbed gaseous kinematics within ionization cones include NGC 5252 (Held, Capaccioli & Capellaro 1992) and Mkn 573 (Tsvetanov & Walsh 1992). Some galaxies may lack the ionization-cone morphology, but exhibit strong kinematical evidence for wide-angle outflow (e.g., NGC 3516: Mulchaey et al. 1992).
The observationally inferred masses, velocities, and kinetic energies in
these outflows are typically a few x 105-106
M
, 100-400
km s-1, and 1052-1055 erg,
respectively. Kinetic energy fluxes range up to
1041 erg
s-1. If the flows last as long as 108 yrs,
the total kinetic energy released could be as high as
1056
erg. These energy fluxes
and energies are typically at least 1-3 orders of magnitude smaller than
is characteristic
of the morphologically similar "superwinds" driven by starburst activity
in luminous far-infrared galaxies
(Heckman, Armus, &
Miley 1990).
Of course, more luminous AGN
could drive winds of comparable power to the luminous far-infrared
galaxies, but such
has yet to be demonstrated observationally. Production of both a highly
collimated, fast jet and a wide-angle, slower wind may be a generic feature of
AGN. This property
could have particular significance for the AGN paradigm: perhaps jets
result from
electromagnetic extraction of rotational energy from the black hole
(e.g.,
Blandford 1990),
while the wider-angle flows are collimated by the associated
accretion disk, by a larger-scale molecular torus
(Krolik & Begelman
1986),
or even by the galaxy disk.