Looking for Signatures of AGN Feedback in Radio-Quiet AGN
First author: Preeti Kharb
(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.