A biconical ionised gas outflow and evidence of positive feedback in NGC 7172 uncovered by MIRI/JWST

Abstract

We present observations of the type-2 Seyfert NGC\,7172 obtained with the medium-resolution spectrometer (MRS) of the Mid-Infrared Instrument (MIRI) on board the James Webb Space Telescope (JWST). This galaxy hosts one of the lowest ionised gas mass outflow rates ($ M out sun $) in a sample of six active galactic nuclei (AGN) with similar bolometric luminosities (log L$_ bol $) within the Galactic Activity, Torus, and Outflow Survey (GATOS). We aim to understand the properties of the ionised gas outflow and its impact on the host galaxy. We mainly used the ionised gas emission lines from the neon transitions, which cover a broad range of ionisation potentials (IPs) from sim 20\,eV to sim 130\,eV. We applied parametric and non-parametric methods to characterise the line emission and kinematics. The low excitation lines (IP\,$<$\,25\,eV, e.g. Ne\,II ) trace the rotating disc emission. The high excitation lines (IP\,$>$\,90\,eV, e.g. Ne\,V $. In particular Ne\,V and Ne\,VI lines reveal a biconical ionised gas outflow emerging north-south from the nuclear region, extending at least sim 2.5 and 3.8 (projected distance of sim \,450 and 680\,pc, respectively). Most of the emission arising in the northern part of the cone was not previously detected due to obscuration. Given the almost face-on orientation of the outflow and the almost edge-on orientation of the galaxy, NGC\,7172 may be a case of weak coupling. Nevertheless, we found evidence of positive feedback in two distinct outflowing clumps at projected distances of 3.1 sim 560 and 780\,pc) south-west of the AGN. We estimated a star formation rate in these regions using the Ne\,II and Ne\,III sun $, which is sim 10<!PCT!> of that found in the circumnuclear ring. The star formation activity might have been triggered by the interaction between the ionised gas outflow and the interstellar medium of the galaxy.