LMC⁺: Large-scale mapping of [C II] and [O III] in the LMC molecular ridge

I. Dataset and line ratio analyses

¹ Deutsches SOFIA Institut, University of Stuttgart, Pfaffenwaldring 29, 70569 Stuttgart, Germany
² IRAM – Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 Saint-Martin d’Hères, France
³ Université Paris Cité, Université Paris-Saclay, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
⁴ Institute of Space Systems – SOFIA Data Center, University of Stuttgart, Pfaffenwaldring 29, 70569 Stuttgart, Germany
⁵ SOFIA Science Center, USRA, NASA Ames Research Center, M.S. N232-12 Moffett Field, CA 94035, USA
⁶ Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA
⁷ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁸ University of Cincinnati, Clermont College, 4200 Clermont College Drive, Batavia, OH 45103, USA
⁹ Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany
¹⁰ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
¹¹ Universität Heidelberg, Zentrum f. Astronomie, Institut f. Theoretische Astrophysik, A.-Ueberle-Str 2, 69120 Heidelberg, Germany
¹² Cosmic Origins Of Life (COOL) Research DAO, coolresearch.io
¹³ Astronomy Department, University of Illinois, Urbana, IL 61801, USA
¹⁴ CNRS, IRAP, 9 Av. du Colonel Roche, BP 44346, 31028 Toulouse cedex 4, France
¹⁵ Department of Astronomy, University of Virginia, PO Box 3818, Charlottesville, VA 22903, USA
¹⁶ Lockheed Martin Solar & Astrophysics Laboratory, Palo Alto, CA 94304, USA
¹⁷ Université Paris-Saclay, Université Paris-Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
¹⁸ Astro Space Center of P.N. Lebedev Physics Institute (ACS LPI), Moscow 117997, Russia
¹⁹ Space Science Institute, 4765 Walnut Street, Suite 205, Boulder, CO 80301, USA
²⁰ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
²¹ NSF’s NOIRLab, 950 N. Cherry Avenue, Tucson, AZ 85719, USA
²² Universidad Autónoma de Chile, Nucleo Astroquimica y Astrofisica, Avda Pedro de Valdivia 425, Providencia, Santiago de Chile, Chile

^★ Corresponding author: fischer@iram.fr

Received: 5 June 2025
Accepted: 1 September 2025

Abstract

Context. The fundamental process of star formation in galaxies involves the intricate interplay between the fueling of star formation via molecular gas and the feedback from recently formed massive stars that can, in turn, hinder the conversion of gas into stars. This process, by which galaxies evolve, is also closely connected to the intrinsic properties of the interstellar medium (ISM), such as structure, density, pressure, and metallicity.

Aims. To study the role that different molecular and atomic phases of the ISM play in star formation, and to characterize their physical conditions, we zoom into our nearest neighboring galaxy, the Large Magellanic Cloud (LMC; 50 kpc), the most convenient laboratory in which to study the effects of the lower metal abundance on the properties of the ISM. The LMC offers a view of the ISM and star formation conditions in a low-metallicity (Z ~ 0.5 Z_⊙) environment similar, in that regard, to the epoch of the peak of star formation in the earlier Universe (z ~ 1.5). Following up on studies carried out at galactic scales in low-Z galaxies, we present an unprecedentedly detailed analysis of well-known star-forming regions (SFRs) at a spatial resolution of a few parsecs.

Methods. We mapped a 610pc × 260pc region in the LMC molecular ridge in [C II]λ158 µm and the [O III]λ88 µm using the FIFI-LS instrument on the SOFIA telescope. We compared the data with the distribution of the CO(2−1) emission from ALMA, the modeled total infrared luminosity, and the Spitzer/MIPS 24 µm continuum and Hα.

Results. We present new large maps of [C II] and [O III] and perform a first comparison with CO(2−1) line and L_TIR emission. We also provide a detailed description of the observing strategy with SOFIA/FIFI-LS and the data reduction process.

Conclusions. We find that [C II] and [O III] emission is associated with the SFRs in the molecular ridge, but also extends throughout the mapped region, and is not obviously associated with ongoing star formation. The CO emission is clumpier than the [C II] emission and we find plentiful [C II] present where there is little CO emission, possibly holding important implications for “CO-dark” gas. We find a clear trend of the L_[C II]/L_TIR ratio decreasing with increasing L_TIR in the full range. This suggests a strong link between the “[C II]-deficit” and the local physical conditions instead of global properties.