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.


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

National Radio Astronomy Observatory

University of Virginia

College of Liberal Arts and Sciences

Y. Song

Atacama Large Millimeter-submillimeter Array (ALMA)

European Southern Observatory Santiago

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

European University Cyprus

Foundation for Research and Technology-Hellas (FORTH)

T. Diaz-Santos

Foundation for Research and Technology-Hellas (FORTH)

European University Cyprus

Christopher C. Hayward

Flatiron Institute

Thomas Lai

California Institute of Technology (Caltech)

Anne M. Medling

University of Toledo

ARC Centre of Excellence for All-sky Astrophysics

C. Ricci

Beijing University of Technology

Diego Portales University

U. Vivian

University of California at Irvine (UCI)

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 966 2 166

Subject Categories

Astronomy, Astrophysics and Cosmology

Atom and Molecular Physics and Optics



More information

Latest update

7/3/2024 8