A Caltech Library Service

Studying the ISM at ∼10 pc scale in NGC 7793 with MUSE. II. Constraints on the oxygen abundance and ionising radiation escape

Della Bruna, Lorenza and Adamo, Angela and Lee, Janice C. and Smith, Linda J. and Krumholz, Mark and Bik, Arjan and Calzetti, Daniela and Fox, Anne and Fumagalli, Michele and Grasha, Kathryn and Messa, Matteo and Östlin, Göran and Walterbos, Rene and Wofford, Aida (2021) Studying the ISM at ∼10 pc scale in NGC 7793 with MUSE. II. Constraints on the oxygen abundance and ionising radiation escape. Astronomy and Astrophysics, 650 . Art. No. A103. ISSN 0004-6361. doi:10.1051/0004-6361/202039402.

[img] PDF - Published Version
See Usage Policy.

[img] PDF - Accepted Version
See Usage Policy.


Use this Persistent URL to link to this item:


Context. Feedback from massive stars affects the interstellar medium (ISM) from the immediate surroundings of the stars (parsec scales) to galactic (kiloparsec) scales. High-spatial resolution studies of H II regions are critical to investigate how this mechanism operates. Aims. We study the ionised ISM in NGC 7793 with the MUSE instrument at ESO Very Large Telescope (VLT), over a field of view (FoV) of ∼2 kpc² and at a spatial resolution of ∼10 pc. The aim is to link the physical conditions of the ionised gas (reddening, ionisation status, abundance measurements) within the spatially resolved H II regions to the properties of the stellar populations producing Lyman continuum photons. Methods. The analysis of the MUSE dataset, which provides a map of the ionised gas and a census of Wolf Rayet stars, is complemented with a sample of young star clusters (YSCs) and O star candidates observed with the Hubble Space Telescope (HST) and of giant molecular clouds traced in CO(2–1) emission with the Atacama Large Millimeter/submillimeter Array (ALMA). We estimated the oxygen abundance using a temperature-independent strong-line method. We determined the observed total amount of ionising photons (Q(H⁰)) from the extinction corrected Hα luminosity. This estimate was then compared to the expected Q(H⁰) obtained by summing the contributions of YSCs and massive stars. The ratio of the two values gives an estimate for the escape fraction (f_(esc)) of photons in the region of interest. We used the [S II]/[O III] ratio as a proxy for the optical depth of the gas and classified H II regions into ionisation bounded, or as featuring channels of optically thin gas. We compared the resulting ionisation structure with the computed f_(esc). We also investigated the dependence of f_(esc) on the age spanned by the stellar population in each region. Results. We find a median oxygen abundance of 12 + log(O/H) ∼ 8.37, with a scatter of 0.25 dex, which is in agreement with previous estimates for our target. We furthermore observe that the abundance map of H II regions is rich in substructures, surrounding clusters and massive stars, although clear degeneracies with photoionisation are also observed. From the population synthesis analysis, we find that YSCs located in H II regions have a higher probability of being younger and less massive as well as of emitting a higher number of ionising photons than clusters in the rest of the field. Overall, we find f_(esc,HII) = 0.67_(−0.12)^(+0.08) for the population of H II regions. We also conclude that the sources of ionisation observed within the FoV are more than sufficient to explain the amount of diffuse ionised gas (DIG) observed in this region of the galaxy. We do not observe a systematic trend between the visual appearance of H II regions and f_(esc), pointing to the effect of 3D geometry in the small sample probed.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Adamo, Angela0000-0002-8192-8091
Lee, Janice C.0000-0002-2278-9407
Smith, Linda J.0000-0002-0806-168X
Krumholz, Mark0000-0003-3893-854X
Bik, Arjan0000-0001-8068-0891
Calzetti, Daniela0000-0002-5189-8004
Fumagalli, Michele0000-0001-6676-3842
Grasha, Kathryn0000-0002-3247-5321
Messa, Matteo0000-0003-1427-2456
Östlin, Göran0000-0002-3005-1349
Walterbos, Rene0000-0002-0782-3064
Wofford, Aida0000-0001-8289-3428
Additional Information:© 2021 ESO. Article published by EDP Sciences. Received 11 September 2020; Accepted 15 April 2021; Published online 15 June 2021. We would like to thank the anonymous referee for the constructive feedback on the second draft of the manuscript. This work is based on observations collected at the European Southern Observatory under ESO programme 60.A-9188(A). A.A. acknowledges the support of the Swedish Research Council, Vetenskapsrådet, and the Swedish National Space Agency (SNSA). This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 757535). This research made use of Astropy (, a community-developed core Python package for Astronomy (Astropy Collaboration 2013, 2018).
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Swedish Research CouncilUNSPECIFIED
Swedish National Space AgencyUNSPECIFIED
European Research Council (ERC)757535
Subject Keywords:galaxies: ISM – HII regions – galaxies: individual: NGC7793 – ISM: structure – ISM: general
Record Number:CaltechAUTHORS:20210715-205748006
Persistent URL:
Official Citation:Studying the ISM at ∼10 pc scale in NGC 7793 with MUSE - II. Constraints on the oxygen abundance and ionising radiation escape. Lorenza Della Bruna, Angela Adamo, Janice C. Lee, Linda J. Smith, Mark Krumholz, Arjan Bik, Daniela Calzetti, Anne Fox, Michele Fumagalli, Kathryn Grasha, Matteo Messa, Göran Östlin, Rene Walterbos and Aida Wofford. A&A, 650 (2021) A103; DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109858
Deposited By: Tony Diaz
Deposited On:15 Jul 2021 21:40
Last Modified:15 Jul 2021 21:40

Repository Staff Only: item control page