Preeti Kharb, Silpa Sasikumar
Abstract
(Abridged) In this article, we discuss the state of ``AGN feedback'' in radio-quiet (RQ) AGN. This study involves heterogeneous samples of nearby Seyfert and LINER galaxies as well as QSOs that have been observed at low radio frequencies (few ~100 MHz) with the GMRT and ~GHz frequencies with the VLA and VLBA. These multi-frequency, multi-resolution observations detect a range of arcsecond-scale radio spectral indices that are consistent with the presence of multiple contributors including starburst winds and AGN jets or winds; steep spectrum ``relic'' emission is observed as well. Polarization-sensitive data from the VLA and GMRT suggest that the radio outflows are stratified (e.g., in IIIZw2, Mrk231); distinct polarization signatures suggest that there could either be a ``spine + sheath'' structure in the radio outflow, or there could be a ``jet + wind'' structure. Similar nested biconical outflows can also explain the VLBA and SDSS emission-line data in the KISSR sample of double-peaked emission-line Seyfert and LINER galaxies. Furthermore, the modeling of the emission-lines with plasma modeling codes such as MAPPINGS indicates that parsec-scale jets and winds in these sources can disturb or move the narrow-line region gas clouds via the ``shock + precursor'' mechanism. Apart from the presence of ``relic'' emission, several Seyfert and LINER galaxies show clear morphological signatures of episodic jet activity. In one such source, NGC2639, at least four distinct episodes of jets are observed, the largest one of which was only detectable at 735 MHz with the GMRT. Additionally, a ~6 kpc hole in the CO molecular gas along with a dearth of young stars in the center of its host galaxy is observed. This suggests a link between episodic jet activity in RQ AGN and ``AGN feedback'' influencing the evolution of their host galaxies.