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A tale of two DIGs: the relative role of H II regions and low-mass hot evolved stars in powering the diffuse ionised gas (DIG) in PHANGS-MUSE galaxies

We use integral field spectroscopy from the PHANGS-MUSE survey, which resolves the ionised interstellar medium structure at ∼50 pc resolution in 19 nearby spiral galaxies, to study the origin of the diffuse ionised gas (DIG). We examine the physical conditions of the diffuse gas by first removing mo...

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Main Authors: Belfiore, Francesco (Author) , Santoro, Francesco (Author) , Groves, B. (Author) , Schinnerer, Eva (Author) , Kreckel, Kathryn (Author) , Glover, Simon (Author) , Klessen, Ralf S. (Author) , Emsellem, E. (Author) , Blanc, G. A. (Author) , Congiu, E. (Author) , Barnes, A. T. (Author) , Boquien, M. (Author) , Chevance, Mélanie (Author) , Dale, D. A. (Author) , Kruijssen, Diederik (Author) , Leroy, A. K. (Author) , Pan, Hsi-An (Author) , Pessa, Ismael (Author) , Schruba, A. (Author) , Williams, Thomas G. (Author)
Format: Article (Journal)
Language:English
Published: 01 March 2022
In: Astronomy and astrophysics
Year: 2022, Volume: 659, Pages: 1-30
ISSN:1432-0746
DOI:10.1051/0004-6361/202141859
Online Access:Verlag, lizenzpflichtig, Volltext: https://doi.org/10.1051/0004-6361/202141859
Verlag, lizenzpflichtig, Volltext: https://www.aanda.org/articles/aa/abs/2022/03/aa41859-21/aa41859-21.html
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Author Notes:F. Belfiore, F. Santoro, B. Groves, E. Schinnerer, K. Kreckel, S.C.O. Glover, R.S. Klessen, E. Emsellem, G.A. Blanc, E. Congiu, A.T. Barnes, M. Boquien, M. Chevance, D.A. Dale, J.M. Diederik Kruijssen, A.K. Leroy, H.-A. Pan, I. Pessa, A. Schruba, and T.G. Williams
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Summary:We use integral field spectroscopy from the PHANGS-MUSE survey, which resolves the ionised interstellar medium structure at ∼50 pc resolution in 19 nearby spiral galaxies, to study the origin of the diffuse ionised gas (DIG). We examine the physical conditions of the diffuse gas by first removing morphologically defined H II regions and then binning the low-surface-brightness areas to achieve significant detections of the key nebular lines in the DIG. A simple model for the leakage and propagation of ionising radiation from H II regions is able to reproduce the observed distribution of H<i>α<i/> in the DIG. This model infers a typical mean free path for the ionising radiation of 1.9 kpc for photons propagating within the disc plane. Leaking radiation from H II regions also explains the observed decrease in line ratios of low-ionisation species ([S II]/H<i>α<i/>, [N II]/H<i>α<i/>, and [O I]/H<i>α<i/>) with increasing H<i>α<i/> surface brightness (Σ<sub>H<i>α<i/><sub/>). Emission from hot low-mass evolved stars, however, is required to explain: (1) the enhanced low-ionisation line ratios observed in the central regions of some of the galaxies in our sample; (2) the observed trends of a flat or decreasing [O III]/H<i>β<i/> with Σ<sub>H<i>α<i/><sub/>; and (3) the offset of some DIG regions from the typical locus of H II regions in the Baldwin-Phillips-Terlevich (BPT) diagram, extending into the area of low-ionisation (nuclear) emission-line regions (LI[N]ERs). Hot low-mass evolved stars make a small contribution to the energy budget of the DIG (2% of the galaxy-integrated H<i>α<i/> emission), but their harder spectra make them fundamental contributors to [O III] emission. The DIG might result from a superposition of two components, an energetically dominant contribution from young stars and a more diffuse background of harder ionising photons from old stars. This unified framework bridges observations of the Milky Way DIG with LI(N)ER-like emission observed in nearby galaxy bulges.
Item Description:Gesehen am 20.04.2022
Physical Description:Online Resource
ISSN:1432-0746
DOI:10.1051/0004-6361/202141859

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