High-resolution ALMA observations of H2S in LIRGs: Dense gas and shocks in outflows and circumnuclear disks - UTU Research Portal

A1 Refereed original research article in a scientific journal

High-resolution ALMA observations of H2S in LIRGs: Dense gas and shocks in outflows and circumnuclear disks

Authors: Sato, Mamiko T.; Aalto, S.; König, Sabine; Kohno, Kotaro; Viti, Serena; Gorski, Mark; Combes, Francoise; Garcia-Burillo, Santiago; Harada, Nanase; van der Werf, Paul; Otter, Justin; Muller, S.; Nishimura, Yuri; Gallagher, John S.; Evans, Aaron S.; Dasyra, Kalliopi M.; Kotilainen, Jari K.

Publisher: EDP Sciences

Publication year: 2025

Journal: Astronomy and Astrophysics

Article number: A156

Volume: 702

ISSN: 0004-6361

eISSN: 1432-0746

DOI: https://doi.org/10.1051/0004-6361/202555589

Publication's open availability at the time of reporting: Open Access

Publication channel's open availability : Open Access publication channel

Web address : https://doi.org/10.1051/0004-6361/202555589

Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/505466817

Abstract

Context

Molecular gas plays a critical role in regulating star formation and nuclear activity in galaxies. Sulphur-bearing molecules, such as H₂S, are sensitive to the physical and chemical environments in which they reside and are potential tracers of shocked, dense gas in galactic outflows and active galactic nuclei (AGNs).

Aims. We aim to investigate the origin of H₂S emission and its relation to dense gas and outflow activity in the central regions of nearby infrared-luminous galaxies.

Methods

We present Atacama Large Millimeter/submillimeter Array (ALMA) Band 5 observations of the ortho-H₂S 1_1, 0 − 1_0, 1 transition in three nearby galaxies: NGC 1377, NGC 4418, and NGC 1266. We performed radiative transfer modelling using RADEX to constrain the physical conditions of the H₂S-emitting gas and compare the results to ancillary CO and continuum data.

Results

We detect compact H₂S emission in all three galaxies, arising from regions smaller than ∼150 pc. The H₂S spectral profiles exhibit broad line wings, suggesting an association with outflowing or shocked gas. In NGC 4418, H₂S also appears to be tracing gas that is counter-rotating. A peculiar redshifted emission feature may be inflowing gas, or possibly a slanted outflow. RADEX modelling indicates that the H₂S-emitting gas has high densities (n_H₂ ≳ 10⁷ cm⁻³) and moderately warm temperatures (40−200 K). The derived densities exceed those inferred from CO observations, implying that H₂S traces denser regions of the ISM.

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Funding information in the publication:
The Nordic ARC node is funded through Swedish Research Council grant No 2019-00208. MS and SA gratefully acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 789410, PI: S. Aalto). Part of this work was supported by the German Deutsche Forschungsgemeinschaft, DFG project number Ts 17/2–1. SV has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme MOPPEX 833460. YN gratefully acknowledges support from JSPS KAKENHI Grant Numbers JP23K13140 and JP23K20035.