A tale of two DIGs

• Verfasst von: Belfiore, Francesco [VerfasserIn]
• Verfasst von: Santoro, Francesco [VerfasserIn]
• Verfasst von: Groves, B. [VerfasserIn]
• Verfasst von: Schinnerer, Eva [VerfasserIn]
• Verfasst von: Kreckel, Kathryn [VerfasserIn]
• Verfasst von: Glover, Simon [VerfasserIn]
• Verfasst von: Klessen, Ralf S. [VerfasserIn]
• Verfasst von: Emsellem, E. [VerfasserIn]
• Verfasst von: Blanc, G. A. [VerfasserIn]
• Verfasst von: Congiu, E. [VerfasserIn]
• Verfasst von: Barnes, A. T. [VerfasserIn]
• Verfasst von: Boquien, M. [VerfasserIn]
• Verfasst von: Chevance, Mélanie [VerfasserIn]
• Verfasst von: Dale, D. A. [VerfasserIn]
• Verfasst von: Kruijssen, Diederik [VerfasserIn]
• Verfasst von: Leroy, A. K. [VerfasserIn]
• Verfasst von: Pan, Hsi-An [VerfasserIn]
• Verfasst von: Pessa, Ismael [VerfasserIn]
• Verfasst von: Schruba, A. [VerfasserIn]
• Verfasst von: Williams, Thomas G. [VerfasserIn]
• Titel: A tale of two DIGs
• Titelzusatz: the relative role of H II regions and low-mass hot evolved stars in powering the diffuse ionised gas (DIG) in PHANGS-MUSE galaxies
• Verf.angabe: 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
• E-Jahr: 2022
• Jahr: 01 March 2022
• Umfang: 30 S.
• Fussnoten: Gesehen am 20.04.2022
• Titel Quelle: Enthalten in: Astronomy and astrophysics
• Ort Quelle: Les Ulis : EDP Sciences, 1969
• Jahr Quelle: 2022
• Band/Heft Quelle: 659(2022), Artikel-ID A26, Seite 1-30
• ISSN Quelle: 1432-0746
• DOI: doi:10.1051/0004-6361/202141859
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1798321645

Abstract

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.