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

¹ Centro de Astrobiología (CAB) CSIC-INTA, Camino bajo el Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
² Instituto de Física Fundamental, CSIC, Calle Serrano 123, 28006 Madrid, Spain
³ Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
⁴ Observatorio Astronómico Nacional (OAN-IGN) – Observatorio de Madrid, Alfonso XII, 3, 28014 Madrid, Spain
⁵ Instituto de Astrofísica de Canarias, C/ Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁶ Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
⁷ Max Planck Institute for Extraterrestrial Physics (MPE), Giessenbachstr.1, 85748 Garching, Germany
⁸ Department of Physics and Astronomy, University of Alaska Anchorage, Anchorage, AK 99508-4664, USA
⁹ Department of Physics and Astronomy, The University of Texas at San Antonio, 1 UTSA Circle, San Antonio, TX 78249, USA
¹⁰ Department of Physics, University of Alaska, Fairbanks, AL 99775-5920, USA
¹¹ School of Mathematics, Statistics and Physics, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
¹² Kavli Institute for Particle Astrophysics & Cosmology (KIPAC), Stanford University, Stanford, CA 94305, USA
¹³ Departmento de Física de la Tierra y Astrofísica, Fac. de CC Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
¹⁴ Instituto de Física de Partículas y del Cosmos IPARCOS, Fac. CC Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
¹⁵ Cahill Center for Astrophysics, California Institute of Technology, 1216 East California Boulevard, Pasadena, CA 91125, USA
¹⁶ LERMA, Observatoire de Paris, Collège de France, PSL University, CNRS, Sorbonne University, France, Paris
¹⁷ Institute of Astrophysics, Foundation for Research and Technology-Hellas (FORTH), Heraklion 70013, Greece
¹⁸ School of Sciences, European University Cyprus, Diogenes street, Engomi, 1516 Nicosia, Cyprus
¹⁹ School of Physics & Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK
²⁰ Instituto de Radioastronomía y Astrofísica (IRyA), Universidad Nacional Autónoma de México, Antigua Carretera a Pátzcuaro 8701, ExHda. San José de la Huerta, Morelia, Michoacán 58089, Mexico
²¹ National Astronomical Observatory of Japan, National Institutes of Natural Sciences (NINS), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
²² Department of Astronomy, School of Science, Graduate University for Advanced Studies (SOKENDAI), Mitaka, Tokyo 181-8588, Japan
²³ Telespazio UK for the European Space Agency (ESA), ESAC, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Spain
²⁴ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
²⁵ Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago, Chile
²⁶ Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, China
²⁷ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Sorbonne Paris Citeé, 5 place Jules Janssen, 92195 Meudon, France
²⁸ Astronomical Observatory, Volgina 7, 11060 Belgrade, Serbia
²⁹ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281-S9, Gent 9000, Belgium
³⁰ Centro de Astrobiología (CAB), CSIC-INTA, Ctra. de Ajalvir, km 4, 28850 Torrejón de Ardoz, Madrid, Spain
³¹ Centre for Extragalactic Astronomy, Durham University, South Road, Durham DH1 3LE, UK

Received: 5 April 2024
Accepted: 21 July 2024

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 (Ṁ_out ∼ 0.005 M_⊙ yr⁻¹) in a sample of six active galactic nuclei (AGN) with similar bolometric luminosities (log L_bol ∼ 44 erg s⁻¹) 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 ∼20 eV to ∼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]), which are likely photoionised exclusively by the AGN, are expanding in the direction nearly perpendicular to the disc of the galaxy, with maximum projected velocities in the range of ∼350–500 km s⁻¹. In particular, [Ne V] and [Ne VI] lines reveal a biconical ionised gas outflow emerging north-south from the nuclear region, extending at least ∼2.5″ N and 3.8″ S (projected distance of ∼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″ and 4.3″ (i.e. ∼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] luminosities of 0.08 M_⊙ yr⁻¹, which is ∼10% 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.