Lorenza Della Bruna
Studying the ISM at ∼10 pc scale in NGC 7793 with MUSE: I. Data description and properties of the ionised gas
Della Bruna, Lorenza; Adamo, Angela; Bik, Arjan; Fumagalli, Michele; Walterbos, Rene; Östlin, Göran; Bruzual, Gustavo; Calzetti, Daniela; Charlot, Stephane; Grasha, Kathryn; Smith, Linda J.; Thilker, David; Wofford, Aida
Authors
Angela Adamo
Arjan Bik
Professor Michele Fumagalli michele.fumagalli@durham.ac.uk
Academic Visitor
Rene Walterbos
Göran Östlin
Gustavo Bruzual
Daniela Calzetti
Stephane Charlot
Kathryn Grasha
Linda J. Smith
David Thilker
Aida Wofford
Abstract
Context. Studies of nearby galaxies reveal that around 50% of the total Hα luminosity in late-type spirals originates from diffuse ionised gas (DIG), which is a warm, diffuse component of the interstellar medium that can be associated with various mechanisms, the most important ones being “leaking” HII regions, evolved field stars, and shocks. Aims. Using MUSE Wide Field Mode adaptive optics-assisted data, we study the condition of the ionised medium in the nearby (D = 3.4 Mpc) flocculent spiral galaxy NGC 7793 at a spatial resolution of ∼10 pc. We construct a sample of HII regions and investigate the properties and origin of the DIG component. Methods. We obtained stellar and gas kinematics by modelling the stellar continuum and fitting the Hα emission line. We identified the boundaries of resolved HII regions based on their Hα surface brightness. As a way of comparison, we also selected regions according to the Hα/[SII] line ratio; this results in more conservative boundaries. Using characteristic line ratios and the gas velocity dispersion, we excluded potential contaminants, such as supernova remnants (SNRs) and planetary nebulae (PNe). The continuum subtracted HeII map was used to spectroscopically identify Wolf Rayet stars (WR) in our field of view. Finally, we computed electron densities and temperatures using the line ratio [SII]6716/6731 and [SIII]6312/9069, respectively. We studied the properties of the ionised gas through “BPT” emission line diagrams combined with velocity dispersion of the gas. Results. We spectroscopically confirm two previously detected WR and SNR candidates and report the discovery of the other seven WR candidates, one SNR, and two PNe within our field of view. The resulting DIG fraction is between ∼27 and 42% depending on the method used to define the boundaries of the HII regions (flux brightness cut in Hα = 6.7 × 10−18 erg s−1 cm−2 or Hα/[SII] = 2.1, respectively). In agreement with previous studies, we find that the DIG exhibits enhanced [SII]/Hα and [NII]/Hα ratios and a median temperature that is ∼3000 K higher than in HII regions. We also observe an apparent inverse correlation between temperature and Hα surface brightness. In the majority of our field of view, the observed [SII]6716/6731 ratio is consistent within 1σ with ne < 30 cm−3, with an almost identical distribution for the DIG and HII regions. The velocity dispersion of the ionised gas indicates that the DIG has a higher degree of turbulence than the HII regions. Comparison with photoionisation and shock models reveals that, overall, the diffuse component can only partially be explained via shocks and that it is most likely consistent with photons leaking from density bounded HII regions or with radiation from evolved field stars. Further investigation will be conducted in a follow-up paper.
Citation
Della Bruna, L., Adamo, A., Bik, A., Fumagalli, M., Walterbos, R., Östlin, G., …Wofford, A. (2020). Studying the ISM at ∼10 pc scale in NGC 7793 with MUSE: I. Data description and properties of the ionised gas. Astronomy & Astrophysics, 635, Article A134. https://doi.org/10.1051/0004-6361/201937173
Journal Article Type | Article |
---|---|
Acceptance Date | Feb 13, 2020 |
Online Publication Date | Mar 23, 2020 |
Publication Date | Mar 31, 2020 |
Deposit Date | Apr 29, 2020 |
Publicly Available Date | Apr 29, 2020 |
Journal | Astronomy and astrophysics. |
Print ISSN | 0004-6361 |
Electronic ISSN | 1432-0746 |
Publisher | EDP Sciences |
Peer Reviewed | Peer Reviewed |
Volume | 635 |
Article Number | A134 |
DOI | https://doi.org/10.1051/0004-6361/201937173 |
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Copyright Statement
Della Bruna, Lorenza, Adamo, Angela, Bik, Arjan, Fumagalli, Michele, Walterbos, Rene, Östlin, Göran, Bruzual, Gustavo, Calzetti, Daniela, Charlot, Stephane, Grasha, Kathryn, Smith, Linda J., Thilker, David & Wofford, Aida (2020). Studying the ISM at ∼10 pc scale in NGC 7793 with MUSE. Astronomy & Astrophysics 635: A134 reproduced with permission, © ESO.
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