MICONIC: JWST/MIRI MRS observations of the nuclear and circumnuclear regions of Mrk 231

¹ Centro de Astrobiología (CAB), CSIC-INTA, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
² Telespazio UK for the European Space Agency (ESA), ESAC, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Spain
³ Sorbonne Université, CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98bis bd Arago, 75014 Paris, France
⁴ Institut Universitaire de France, Ministère de l’Enseignement Supérieur et de la Recherche, 1 Rue Descartes, 75231 Paris Cedex 05, France
⁵ Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
⁶ UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ Scotland, UK
⁷ Centro de Astrobiología (CAB), CSIC-INTA, Ctra. de Ajalvir km 4, Torrejón de Ardoz, 28850 Madrid, Spain
⁸ European Space Agency, c/o Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁹ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50939 Köln, Germany
¹⁰ Max-Planck Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, 53121 Bonn, Germany
¹¹ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, 9000 Gent, Belgium
¹² LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Sorbonne Paris Citeé, 5 Place Jules Janssen, 92195 Meudon, France
¹³ Centre for Extragalactic Astronomy, Durham University, South Road, Durham DH1 3LE, UK
¹⁴ Department of Astronomy, Stockholm University, The Oskar Klein Centre, AlbaNova, 106 91 Stockholm, Sweden
¹⁵ Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
¹⁶ Dept. of Astrophysics, University of Vienna, Türkenschanzstr. 17, 1180 Vienna, Austria
¹⁷ ETH Zürich, Institute for Particle Physics and Astrophysics, Wolfgang-Pauli-Str. 27, 8093 Zürich, Switzerland
¹⁸ Max Planck Institute for Astronomy, Konigstuhl 17, 69117 Heidelberg, Germany
¹⁹ Universite Paris-Saclay, Universite Paris Cite, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France

Received: 22 March 2024
Accepted: 27 June 2024

Abstract

We present JWST/MIRI MRS spatially resolved ∼5 − 28 μm observations of the central ∼4 − 8 kpc of the ultraluminous infrared galaxy and broad absorption line quasar Mrk 231. These are part of the Mid-Infrared Characterization of Nearby Iconic galaxy Centers (MICONIC) program of the MIRI European Consortium guaranteed time observations. No high excitation lines (i.e., [Mg V] at 5.61 μm or [Ne V] at 14.32 μm) typically associated with the presence of an active galactic nucleus (AGN) are detected in the nuclear region of Mrk 231. This is likely due to the intrinsically X-ray weak nature of its quasar. Some intermediate ionization potential lines, for instance, [Ar III] at 8.99 μm and [S IV] at 10.51 μm, are not detected either, even though they are clearly observed in a star-forming region ∼920 pc south-east of the AGN. Thus, the strong nuclear mid-infrared (mid-IR) continuum is also in part hampering the detection of faint lines in the nuclear region. The nuclear [Ne III]/[Ne II] line ratio is consistent with values observed in star-forming galaxies. Moreover, we resolve for the first time the nuclear starburst in the mid-IR low-excitation line emission (size of ∼400 pc, FWHM). Several pieces of evidence also indicate that it is partly obscured even at these wavelengths. At the AGN position, the ionized and warm molecular gas emission lines have modest widths (W₈₀ ∼ 300 km s⁻¹). There are, however, weak blueshifted wings reaching velocities v₀₂ ≃ − 400 km s⁻¹ in [Ne II]. The nuclear starburst is at the center of a large (∼8 kpc), massive rotating disk with widely-spread, low velocity outflows. Given the high star formation rate of Mrk 231, we speculate that part of the nuclear outflows and the large-scale non-circular motions observed in the mid-IR are driven by its powerful nuclear starburst.