Infrared view of the multiphase ISM in NGC 253 I. Observations and fundamental parameters of the ionised gas

• Published in: arXiv.org
• Main Authors: Beck, André, Lebouteiller, Vianney, Madden, Suzanne, Iserlohe, Christof, Krabbe, Alfred, Ramambason, Lise, Fischer, Christian, Kaźmierczak-Barthel, Maja, Latzko, Serina, Juan-Pablo Pérez-Beaupuits
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 30.06.2022
• Subjects: Abundance; Astrochemistry; Depletion; Gas density; H II regions; Heavy elements; Interstellar matter; Massive stars; Metallicity; Optical properties; Optical thickness; Parameters; Physical properties; Physics - Astrophysics of Galaxies; Ratios; Star formation; Starburst galaxies; Vapor phases
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2206.15062

Context. Massive star-formation leads to enrichment with heavy elements of the interstellar medium. On the other hand, the abundance of heavy elements is a key parameter to study the star-formation history of galaxies. Furthermore, the total molecular hydrogen mass, usually determined by converting CO or [C ii] 158 \(\mu\)m luminosities, depends on the metallicity as well. The excitation of metallicity-sensitive emission lines, however, depends on the gas density of H ii regions, where they arise. Aims. We used spectroscopic observations from SOFIA, Herschel, and Spitzer of the nuclear region of the starburst galaxy NGC 253, as well as photometric observations from GALEX, 2MASS, Spitzer, and Herschel in order to derive physical properties such as the optical depth to correct for extinction, as well as the gas density and metallicity of the central region. Methods. Ratios of the integrated line fluxes of several species were utilised to derive the gas density and metallicity. The [O iii] along with the [S iii] and [N ii] line flux ratios for example, are sensitive to the gas density but nearly independent of the local temperature. As these line ratios trace different gas densities and ionisation states, we examined if these lines may originate from different regions within the observing beam. The ([Ne ii] 13 \(\mu\)m + [Ne iii] 16 \(\mu\)m)/Hu \(\alpha\) line flux ratio on the other hand, is independent of the depletion onto dust grains but sensitive to the Ne/H abundance ratio and will be used as a tracer for metallicity of the gas. Results. We derived values for gas phase abundances of the most important species, as well as estimates for the optical depth and the gas density of the ionised gas in the nuclear region of NGC 253. We obtained densities of at least two different ionised components \((< 84\) cm\(^{-3}\) and \(\sim 170 - 212\) cm\(^{-3})\) and a metallicity of solar value.