The onset of jet-ISM interaction in the Seyfert galaxy NGC3079: VLBI study of OH absorption at sub-pc scale
May 02, 2022
May 24, 2022
NGC 3079 is a Seyfert galaxy, which harbors a compact parsec scale radio jet in its centre. Single dish observations reveal OH absorption lines at 6 cm in front of the continuum radio jet, indicating the presence of ambient molecular gas surrounding the jet. However, its spatial and physical relation to the jet is not yet clear due to the lack of high-resolution observations. To shed light on this matter, we have conducted spectral line VLBI observations using the European VLBI Network (EVN). The OH absorption feature near the systemic velocity of NGC 3079 appears in both, the approaching and the receding jet components, but the blue-shifted (130 km/s) absorption is only detected on the tip of the approaching radio jet. The observed velocity is not in accord with the sense of rotation of the pc scale H2O maser disk or sub-kpc scale circumnuclear disk seen in HCN, and thus the blue-shifted absorption is interpreted as a jet-driven outflow. An outward moving jet component seems to accumulate and compress the ambient gas, forming a working surface and absorbing layer, which surrounds the jet head. This scenario is supported by the observed deceleration and brightening of the outer jet component. Follow-up spectral line VLBI studies are desirable to monitor this jet-ISM interaction and to further quantify it.
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