The narrow-line regions of jet-dominated Seyfert galaxies

Growing evidence over the past decade has indicated that low-luminosity active galaxies are often associated with outflows from their nuclei. In particular, a small but important fraction of Seyfert galaxies have extended collimated radio emission on the scales of the narrow-line region (NLR). In most of these cases, the emission-line gas displays morphological and kinematic signatures of disturbance or acceleration by the nuclear jet. Using the STIS spectrograph on the HST, we have obtained high spatial resolution long-slit spectra of six Seyfert galaxies which show clear signs of jet-gas interactions. Combined with HST and ground-based optical and archival radio imaging, we are able to explore these interactions in considerable detail.

The archetypal jet-dominated Seyfert, Mkn 78, provides the richest dataset. Emission line analyses clearly show that the NLR is photoionized by the central AGN, with a. definite preference towards a mixture of optically thin and thick ionized clouds. Ionization by shocks is shown to be unimportant. A detailed dynamical study provides . . strong evidence for a thermally-dominated, slow and dense Seyfert jet, quite unlike the powerful jet thought to be present in classical Radio Galaxies.

A rest of the work involves a study of the 5 objects (Mkn 34, NGC 2110, Mkn 348, Mkn 1066 and NGC 5929). Despite the smaller coverage and depth of these spectra, compared to that of Mkn 78, the larger sample allows us to tease apart the relevant features of jet-cloud interactions within this fairly diverse group of objects. We have isolated a number of key dynamical processes such as cloud shocks and acceleration, ablation, jet bending and drag forces. Other elements of the circumnuclear environment, such as gaseous disks, AGN winds and star-forming regions are also shown to play an important role in our view and interpretation of jet interaction and Seyfert ionization signatures. Our results provide new insights into the nature of nuclear outflows in low-luminosity and radio-quiet AGN.

Note: Abstract extracted from PDF file via OCR.