Full disc [C II] mapping of nearby star-forming galaxies

SOFIA FIFI/LS observations of NGC 3627, NGC 4321, and NGC 6946

¹ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281/S9, 9000 Gent, Belgium
² Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
³ European Southern Observatory (ESO), Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
⁴ Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
⁵ Departamento de Astronomía, Universidad de Concepción, Barrio Universitario, Concepción, Chile
⁶ Deutsches SOFIA Institut, Universität Stuttgart, Pfaffenwaldring 29, D-70569 Stuttgart, Germany
⁷ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
⁸ Max-Planck-Institut für Extraterrestrische Physik, Gießenbachstrasse 1, D-85748 Garching, Germany
⁹ SOFIA-USRA, NASA Ames Research Center, MS N232-12, Moffett Field, CA 94035-1000, USA
¹⁰ Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
¹¹ Department of Astronomy, University of Illinois, 1002 W Green Street, Urbana, IL 61801, USA
¹² National Radio Astronomy Observatory, 520 Edgemont Rd., Charlottesville, VA 22903, USA
¹³ NSF’s NOIRLab, 950 N. Cherry Avenue, Tucson AZ 85719, USA
¹⁴ Dept. Fisica Teorica y del Cosmos, Universidad de Granada, Granada, Spain
¹⁵ STAR Institute, Université de Liège, Quartier Agora, Allée du Six Août 19c, 4000 Liège, Belgium

^⋆ Corresponding author; inja.kovacic@ugent.be

Received: 21 March 2024
Accepted: 28 November 2024

Abstract

Context. As a major cooling line of interstellar gas, the far-infrared 158 μm line from singly ionised carbon [C II] is an important tracer of various components of the interstellar medium in galaxies across all spatial and morphological scales. Yet, there is still not a strong constraint on the origins of [C II] emission.

Aims. In this work, we derive the resolved [C II] star formation rate relation and aim to unravel the complexity of the origin of [C II].

Methods. We used the Field-Imaging Far-Infrared Line Spectrometer on board the Stratospheric Observatory for Infrared Astronomy to map [C II] in three nearby star-forming galaxies at sub-kiloparsec scales, namely, NGC 3627, NGC 4321, and NGC 6946, and we compared these [C II] observations to the galactic properties derived from complementary data from the literature.

Results. We find that the relationship between the [C II] fine structure line and star formation rate shows variations between the galaxies as well as between different environments within each galaxy.

Conclusions. Our results show that the use of [C II] as a tracer for star formation is much more tangled than has previously been suggested within the extragalactic literature, which typically focuses on small regions of galaxies and/or uses large-aperture sampling of many different physical environments. As found within resolved observations of the Milky Way, the picture obtained from [C II] observations is complicated by its local interstellar medium conditions. Future studies will require a larger sample and additional observational tracers, obtained on spatial scales within galaxies, in order to accurately disentangle the origin of [C II] and calibrate its use as a star formation tracer.