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    Nuclear high-ionisation outflow in the Compton-thick AGN NGC 6552 as seen by the JWST mid-infrared instrument

    Álvarez-Márquez, J. and Labiano, A. and Guillard, P. and Dicken, D. and Argyriou, I. and Patapis, P. and Law, D. R. and Kavanagh, Patrick J. and Larson, K. L. and Gasman, D. and Mueller, M. and Alberts, S. and Brandl, B. R. and Colina, L. and García-Marín, M. and Jones, O. C. and Noriega-Crespo, A. and Shivaei, I. and Temim, T. and Wright, G. S. (2023) Nuclear high-ionisation outflow in the Compton-thick AGN NGC 6552 as seen by the JWST mid-infrared instrument. Astronomy & Astrophysics, 672. A108. ISSN 0004-6361

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    Context. During the commissioning of the James Webb Space Telescope (JWST), the mid-infrared instrument (MIRI) observed NGC 6552 with the MIRI Imager and the Medium-Resolution Spectrograph (MRS). NGC 6552 is an active galactic nucleus (AGN) at a redshift of 0.0266 (DL = 120 Mpc) classified as a Seyfert 2 nucleus in the optical and Compton-thick AGN in the X-ray. Aims. This work exemplifies and demonstrates the MRS capabilities to study the mid-infrared (mid-IR) spectra and characterise the physical conditions and kinematics of the ionised and molecular gas in the nuclear regions of nearby galaxies. Methods. MIRI Imager observations covers the full NGC 6552 galaxy at 5.6 µm. MRS observations covers its nuclear region (3.6×4.3 kpc at 17.7–27.9 µm) in a wavelength range between 4.9 and 27.9 µm. These observations were obtained with the aim to investigate the persistence of the MIRI detectors (residual signal left from previous bright source observations). However, NGC 6552 observations demonstrate the performance and power of the MIRI instrument even with a non-optimal observational strategy. Results. We obtained the nuclear, circumnuclear, and central mid-IR spectra of NGC 6552. They provide the first clear observational evidence for a nuclear outflow in NGC 6552. The outflow contributes to 67±7% of the total line flux independent of the ionisation potential (27–187 eV) and critical densities (104–4×106 cm−3 ), showing an average blue-shifted peak velocity of −127±45 km s−1 and an outflow maximal velocity of 698±80 km s−1 . Since the mid-IR photons penetrate dusty regions as efficiently as X-ray keV photons, we interpret these results as the evidence for a highly ionised, non-stratified, AGN-powered, and fast outflowing gas in a low density environment (few 103 cm−3 ) located very close (<0.2 kpc) to the Compton-thick AGN. Nine pure rotational molecular Hydrogen lines are detected and spectrally resolved, and exhibit symmetric Gaussian profiles, consistent with the galactic rotation, and with no evidence of outflowing H2 material. We detect a warm H2 mass of 1.9 ± 1.1 × 107 M� in the central region (1.8 kpc in diameter) of the galaxy, with almost 30% of that mass in the circumnuclear region. Line ratios confirm that NGC 6552 has a Seyfert nucleus with a black hole mass estimated in the range of 0.6–6 million solar masses. Conclusions. This work demonstrates the power of the newly commissioned MIRI Medium Resolution Spectrograph to reveal new insights in the kinematics and ionisation state of the interstellar medium around the dusty nuclear regions of nearby active galaxies.

    Item Type: Article
    Keywords: instrumentation; spectrographs; high angular resolution; galaxies; active; Seyfert; kinematics and dynamics;
    Academic Unit: Faculty of Science and Engineering > Experimental Physics
    Item ID: 18591
    Identification Number:
    Depositing User: Patrick Kavanagh
    Date Deposited: 28 May 2024 13:35
    Journal or Publication Title: Astronomy & Astrophysics
    Publisher: EDP Sciences
    Refereed: Yes
    Use Licence: This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available here

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