NARROW-LINE REGION KINEMATICS IN SEYFERT NUCLEI

We present results of a study of narrow-line region (NLR) kinematics in Seyfert nuclei. The five most important conclusions of this work are as follows: 1. Line profiles of [Fe VII] lambda6087 and [Fe x] lambda6374 require a roughly constant ionization parameter throughout the NLR, assuming these lines are emitted by photoionized gas. 2. Assuming constant ionization parameter, we show that a very simple analytical treatment suffices to describe the important features of more detailed models. These analytical models are a powerful tool for narrowing the range of plausible parameters in a quantitative way. 3. Models which incorporate collimated emission and radial motion show that the NLR must extend inward (or outward) to encompass low-velocity clouds if a significant fraction of the total emission-line flux is contained within a biconical structure. 4. We show explicitly that line profiles alone cannot discriminate between variations in the velocity and variations in the luminosity of clouds throughout the NLR. If line emission is that of constant mass spherical clouds which are conserved in number as they cross the NLR, then the clouds are accelerating outward. On the other hand, if cloud velocity is assumed to decrease outward, then line emission is determined by an alternative to constant mass spherical clouds which are conserved in number. This result assumes constant ionization parameter. 5. Line width correlations with critical density and/or ionization potential, reported in the literature, are best interpreted as correlations with ionization potential alone. The correlations can be understood as a column density effect, in which case they are consistent with both constant ionization parameter and cloud velocity increasing outward. In this scenario, the innermost, lowest velocity clouds are always optically thick to the photoionizing continuum and the outermost, highest velocity clouds are sometimes optically thick, and sometimes they are not. The scenario in agreement with the greatest number of observational considerations consists of clouds which are accelerated outward with v is-proportional-to r1/2 (i.e., constant force) and n(e) is-proportional-to 1/r2. The clouds start out at the inner NLR radius with n(e) almost-equal-to 10(6) cm-3 and with a very large column density (10(23)-10(24) CM-2). These clouds are uniformly accelerated from a few tens of km s-1 to less than or similar 1000 km s-1. When the clouds reach the outer NLR radius, they have n(e) greater than or similar to 10(2) CM-3 and a column density of 10(21)-10(22) CM-2. The clouds maintain an ionization parameter of about 0.3 throughout the NLR.