Issue |
A&A
Volume 665, September 2022
|
|
---|---|---|
Article Number | A85 | |
Number of page(s) | 12 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/202243822 | |
Published online | 13 September 2022 |
Infrared view of the multiphase ISM in NGC 253
I. Observations and fundamental parameters of the ionised gas
1
Deutsches SOFIA Institut, University of Stuttgart, Pfaffenwaldring 29, 70569, Stuttgart
e-mail: abeck@dsi.uni-stuttgart.de
2
Laboratoire AIM, CEA/Service d’Astrophysique, Bât. 709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
3
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
4
Centro de Astro-Ingeniería (AIUC), Pontificia Universidad Católica de Chile, Av. Vicuña Mackena, 4860 Macul, Santiago, Chile
Received:
20
April
2022
Accepted:
28
June
2022
Context. Massive star formation leads to enrichment of the interstellar medium with heavy elements. On the other hand, the abundance of heavy elements is a key parameter with which to study the star-formation history of galaxies. Furthermore, the total molecular hydrogen mass, usually determined by converting CO or [C II]158 μm luminosities, depends on the metallicity as well. However, the excitation of metallicity-sensitive emission lines depends on the gas density of the H II regions where they arise.
Aims. We used spectroscopic observations of the nuclear region of the starburst galaxy NGC 253 from SOFIA, Herschel, and Spitzer, 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 whether or not these lines could originate from different regions within the observing beam. The ([Ne II]13 μm + [Ne III]16 μm)/Hα line flux ratio on the other hand is independent of the depletion onto dust grains but sensitive to the Ne/H abundance ratio and is 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 ∼170−212 cm−3) and a metallicity of solar value.
Key words: galaxies: starburst / galaxies: individual: NGC 253 / infrared: ISM
© A. Beck et al. 2022
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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