High-resolution ALMA observations of H2S in LIRGs: Dense gas and shocks in outflows and circumnuclear disks
Journal article, 2025
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 11, 0 - 10, 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 similar to 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 (nH2 greater than or similar to 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.
galaxies: individual: NGC 1377
radiative transfer
galaxies: jets
galaxies: nuclei
galaxies: individual: NGC 4418
galaxies: individual: NGC 1266
Author
Mamiko Sato
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Susanne Aalto
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Sabine König
Chalmers, Space, Earth and Environment, Onsala Space Observatory
K. Kohno
University of Tokyo
S. Viti
University College London (UCL)
Leiden University
University of Bonn
M. Gorski
Northwestern University
F. Combes
Sorbonne University
S. Garcia-Burillo
Spanish National Observatory (OAN)
N. Harada
National Astronomical Observatory of Japan
P. van der Werf
Leiden University
J. Otter
Johns Hopkins University
Sebastien Muller
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Y. Nishimura
University of Tokyo
J. S. Gallagher
University of Wisconsin Madison
A. S. Evans
National Radio Astronomy Observatory
University of Virginia
K. M. Dasyra
National and Kapodistrian University of Athens
J. K. Kotilainen
University of Turku
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 702 A156Subject Categories (SSIF 2025)
Atom and Molecular Physics and Optics
Astronomy, Astrophysics, and Cosmology
DOI
10.1051/0004-6361/202555589