Spatially-Resolved Narrow Line Region Kinematics in Active Galactic Nuclei

Rice, M.S., Martini, P., Greene, J.E., Pogge, R.W., Shields, J.C., Mulchaey, J.S., and Regan, M.W. 2006, ApJ, 636, 654

We have analyzed Hubble Space Telescope spectroscopy of 24 nearby Active Galactic Nuclei (AGNs) to investigate spatially-resolved gas kinematics in the Narrow Line Region (NLR). These observations effectively isolate the nuclear line profiles on less than 100 parsec scales and are used to investigate the origin of the substantial scatter between the widths of strong NLR lines and the stellar velocity dispersion \sigma_* of the host galaxy, a quantity which relates with substantially less scatter to the mass of the central, supermassive black hole, and more generally characterize variations in the NLR velocity field with radius. We find that line widths measured with STIS at a range of spatial scales systematically underestimate both \sigma_* and the line width measured from ground-based observations, although they do have comparably large scatter to the relation between ground-based NLR line width and \sigma_*. There are no obvious trends in the residuals when compared with a range of host galaxy and nuclear properties. The widths and asymmetries of [OIII] 5007 and [SII] 6716, 6731 as a function of radius exhibit a wide range of behavior. Some of the most common phenomena are substantial width increases from the STIS to the large-scale, ground-based aperture and almost no change in line profile between the unresolved nuclear spectrum and ground-based measurements. We identify asymmetries in a surprisingly large fraction of low-ionization [SII] line profiles and several examples of substantial red asymmetries in both [OIII] and [SII]. These results underscore the complexity of the circumnuclear material that constitutes the NLR and suggests that the scatter in the NLR width and \sigma_* correlation can not be substantially reduced with a simple set of empirical relations.