GOALS-JWST: Mid-infrared Molecular Gas Excitation Probes the Local Conditions of Nuclear Star Clusters and the Active Galactic Nucleus in the LIRG VV 114
Journal article, 2024
The enormous increase in mid-IR sensitivity and spatial and spectral resolution provided by the JWST spectrographs enables, for the first time, detailed extragalactic studies of molecular vibrational bands. This opens an entirely new window for the study of the molecular interstellar medium in luminous infrared galaxies (LIRGs). We present a detailed analysis of rovibrational bands of gas-phase CO, H2O, C2H2, and HCN toward the heavily obscured eastern nucleus of the LIRG VV 114, as observed by NIRSpec and the medium resolution spectrograph on the Mid-InfraRed Instrument (MIRI MRS). Spectra extracted from apertures of 130 pc in radius show a clear dichotomy between the obscured active galactic nucleus (AGN) and two intense starburst regions. We detect the 2.3 μm CO bandheads, characteristic of cool stellar atmospheres, in the star-forming regions, but not toward the AGN. Surprisingly, at 4.7 μm, we find highly excited CO (T ex ≈ 700-800 K out to at least rotational level J = 27) toward the star-forming regions, but only cooler gas (T ex ≈ 200 K) toward the AGN. We conclude that only mid-infrared pumping through the rovibrational lines can account for the equilibrium conditions found for CO and H2O in the deeply embedded starbursts. Here, the CO bands probe regions with an intense local radiation field inside dusty young massive star clusters or near the most massive young stars. The lack of high-excitation molecular gas toward the AGN is attributed to geometric dilution of the intense radiation from the bright point source. An overview of the relevant excitation and radiative transfer physics is provided in an appendix.
Author
Victorine A. Buiten
Leiden University
P. van der Werf
Leiden University
Serena Viti
Leiden University
Lee Armus
California Institute of Technology (Caltech)
Andrew G. Barr
Netherlands Institute for Space Research (SRON)
Loreto Barcos-Munoz
National Radio Astronomy Observatory
University of Virginia
Aaron S. Evans
National Radio Astronomy Observatory
University of Virginia
H. Inami
Hiroshima University
S. T. Linden
University of Arizona
G. Privon
College of Liberal Arts and Sciences
University of Virginia
National Radio Astronomy Observatory
Y. Song
European Southern Observatory Santiago
Atacama Large Millimeter-submillimeter Array (ALMA)
Jeff Rich
Carnegie Observatories
Susanne Aalto
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
P. Appleton
California Institute of Technology (Caltech)
T. Boker
European Space Agency (ESA)
V. Charmandaris
University of Crete
Foundation for Research and Technology-Hellas (FORTH)
European University Cyprus
T. Diaz-Santos
European University Cyprus
Foundation for Research and Technology-Hellas (FORTH)
Christopher C. Hayward
Flatiron Institute
Thomas Lai
California Institute of Technology (Caltech)
Anne M. Medling
ARC Centre of Excellence for All-sky Astrophysics
University of Toledo
C. Ricci
Beijing University of Technology
Diego Portales University
U. Vivian
University of California
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 966 2 166Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
Atom and Molecular Physics and Optics
DOI
10.3847/1538-4357/ad344b