| Issue |
A&A
Volume 669, January 2023
|
|
|---|---|---|
| Article Number | A88 | |
| Number of page(s) | 7 | |
| Section | Extragalactic astronomy | |
| DOI | https://doi.org/10.1051/0004-6361/202244591 | |
| Published online | 16 January 2023 | |
The softness diagram for MaNGA star-forming regions: diffuse ionized gas contamination or local HOLMES predominance?
1
Instituto de Astrofísica de Andalucía (CSIC), Apartado 3004, 18080 Granada, Spain
e-mail: epm@iaa.es
2
Faculty of Physics, Ludwig-Maximilians-Universität, Scheinerstr. 1, 81679 Munich, Germany
3
Main Astronomical Observatory, National Academy of Sciences of Ukraine, 27 Akademika Zabolotnoho St., 03680 Kyiv, Ukraine
4
Dpto. de Física Teórica y del Cosmos, Campus de Fuentenueva, Edificio Mecenas, Universidad de Granada, 18071 Granada, Spain
5
Instituto Carlos I de Física Teórica y Computacional, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain
Received:
25
July
2022
Accepted:
18
November
2022
Aims. We explore the so-called softness diagram – whose main function is to provide the hardness of the ionizing radiation in star-forming regions – in order to check whether hot and old low-mass evolved stars (HOLMES) are significant contributors to the ionization within star-forming regions, as suggested by previous MaNGA data analyses.
Methods. We used the code HCM-TEFF to derive both the ionization parameter and the equivalent effective temperature (T*), adopting models of massive stars and planetary nebulae (PNe), and exploring different sets of emission lines in the softness diagram to figure out the main causes of the observed differences in the softness parameter in the MaNGA and CHAOS star-forming region samples.
Results. We find that the fraction of regions with a resulting T* > 60 kK, which are supposedly ionised by sources harder than massive stars, is considerably larger in the MaNGA (66%) than in the CHAOS (20%) sample when the [S II] λλ 6716,6731 Å emission lines are used in the softness diagram. However, the respective fractions of regions in this regime for both samples are considerably reduced (20% in MaNGA and 10% in CHAOS) when the [N II] emission line at λ 6584 Å is used instead. This may indicate that diffuse ionised gas (DIG) contamination in the lower resolution MaNGA data is responsible for artificially increasing the measured T* as opposed to there being a predominant role of HOLMES in the H II regions.
Key words: galaxies: abundances / galaxies: stellar content / galaxies: star formation
© The Authors 2023
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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