GATOS: missing molecular gas in the outflow of NGC 5728 revealed by JWST

¹ Max Planck Institute for Extraterrestrial Physics (MPE), Giessenbachstr.1, 85748 Garching, Germany
² Instituto de Física Fundamental, CSIC, Calle Serrano 123, 28006 Madrid, Spain
³ Centro de Astrobiología (CSIC-INTA), Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
⁴ Instituto de Astrofísica de Canarias, Calle Vía Láctea, s/n, 38205 La Laguna, Tenerife, Spain
⁵ Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
⁶ Departmento de Física de la Tierra y Astrofísica, Fac. de CC Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
⁷ Instituto de Física de Partículas y del Cosmos IPARCOS, Fac. CC Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
⁸ Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
⁹ School of Mathematics, Statistics and Physics, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
¹⁰ LERMA, Observatoire de Paris, Collège de France, PSL University, CNRS, Sorbonne University, Paris
¹¹ Department of Physics & Astronomy, University of Alaska Anchorage, Anchorage, AK 99508-4664, USA
¹² Institute of Astrophysics, Foundation for Research and Technology-Hellas, Heraklion 70013, Greece
¹³ School of Sciences, European University Cyprus, Diogenes street, Engomi, 1516 Nicosia, Cyprus
¹⁴ Department of Physics and Astronomy, The University of Texas at San Antonio, 1 UTSA Circle, San Antonio, TX 78249, USA
¹⁵ Department of Physics & Astronomy, University of Southampton, Hampshire, SO17 1BJ Southampton, UK
¹⁶ Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
¹⁷ Observatorio Astronómico Nacional (OAN-IGN)-Observatorio de Madrid, Alfonso XII, 3, 28014 Madrid, Spain
¹⁸ Instituto de Radioastronomía y Astrofísica (IRyA), Universidad Nacional Autónoma de México, Antigua Carretera a Pátzcuaro #8701, ExHda. San José de la Huerta, Morelia, Michoacán C.P. 58089, México
¹⁹ National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
²⁰ Department of Astronomy, School of Science, Graduate University for Advanced Studies (SOKENDAI), Mitaka, Tokyo 181-8588, Japan
²¹ Telespazio UK for the European Space Agency, ESAC, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Spain
²² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
²³ Kavli Institute for Particle Astrophysics & Cosmology (KIPAC), Stanford University, Stanford, CA 94305, USA
²⁴ Núcleo de Astronomía de la Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago, Chile
²⁵ Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, PR China
²⁶ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Sorbonne Paris Citeé, 5 place Jules Janssen, 92195 Meudon, France
²⁷ Astronomical Observatory, Volgina 7, 11060 Belgrade, Serbia
²⁸ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281-S9, Gent 9000, Belgium
²⁹ School of Physics and Astronomy, Tel Aviv University, Ramat Aviv 69978, Israel
³⁰ Center for Computational Astrophysics, Flatiron Institute, 162 5th Ave, New York, NY 10010, USA
³¹ Centro de Astrobiología (CAB), CSIC-INTA, Ctra. de Ajalvir, km 4, 28850 Torrejón de Ardoz, Madrid, Spain
³² Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK

Received: 6 March 2024
Accepted: 24 June 2024

Abstract

The ionisation cones of NGC 5728 have a deficit of molecular gas based on millimetre observations of CO (2-1) emission. Although photoionisation from the active nucleus may lead to suppression of this transition, warm molecular gas can still be present. We report the detection of eight mid-infrared rotational H₂ lines throughout the central kiloparsec, including the ionisation cones, using integral field spectroscopic observations with JWST/MIRI MRS. The H₂ line ratios, characteristic of a power-law temperature distribution, indicate that the gas is warmest where it enters the ionisation cone through disk rotation, suggestive of shock excitation. In the nucleus, where the data can be combined with an additional seven ro-vibrational H₂ transitions, we find that moderate velocity (30 km s⁻¹) shocks in dense (10⁵ cm⁻³) gas, irradiated by an external UV field (G₀ = 10³), do provide a good match to the full set. The warm molecular gas in the ionisation cone that is traced by the H₂ rotational lines has been heated to temperatures > 200 K. Outside of the ionisation cone the molecular gas kinematics are undisturbed. However, within the ionisation cone, the kinematics are substantially perturbed, indicative of a radial flow, but one that is quantitatively different from the ionised lines. We argue that this outflow is in the plane of the disk, implying a short 50 pc acceleration zone up to speeds of about 400 km s⁻¹ followed by an extended deceleration over ∼700 pc where it terminates. The deceleration is due to both the radially increasing galaxy mass, and mass-loading as ambient gas in the disk is swept up.