Other
Scientific paper
Oct 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994pasp..106.1111m&link_type=abstract
Publications of the Astronomical Society of the Pacific, v.106, p.1111
Other
Scientific paper
We present results of a study of narrow-line region (NLR) kinematics in Seyfert nuclei. This study has involved extensive modeling which includes collimated emission, radially dependent rotation and turbulence, explicit photoionization calculations, realistic treatments of both internal and external obscuration, and allows for gradients in the electron density and the radial velocity of clouds throughout the NLR. Line profiles of [O II] lambda-3727, [Ne III] lambda-3869, [O III] lambda-5007, [Fe VII] lambda-6087, [Fe X] lambda-6374, [O~I] lambda-6300, H-alpha lambda-6563, and [S II] lambda-6731 are calculated for a wide range of physical conditions throughout the NLR. The model profiles are compared with line profiles derived from data taken with the Palomar Mountain 5-m Hale Telescope as well as with profiles taken from the literature. The five most important conclusions of this work are as follows: 1) Line profiles of [Fe VII] lambda-6087 and [Fe X] lambda-6374 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 in 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 fundamentally 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 not. The scenario in agreement with the largest number of observational considerations consists of clouds which are accelerating outward with v proportional to sqrt{r} (i.e., constant force) and n_e proportional to 1/r^2. The clouds start out at the inner NLR radius with n_e ~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/sec to ~< 1,000 km/sec. When the clouds reach the outer NLR radius, they have n_e ~> 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. (SECTION: Dissertation Summaries)
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