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

Abstract

We use integral field spectroscopy from the PHANGS-MUSE survey, which resolves the ionised interstellar medium at $\sim 50$ 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 HII regions and then binning the low-surface-brightness areas to achieve significant detections of the key nebular lines. A simple model for the leakage and propagation of ionising radiation from HII regions is able to reproduce the observed distribution of H$\alpha$ in the DIG. Leaking radiation from HII regions also explains the observed decrease in line ratios of low-ionisation species ([SII]/H$\alpha$, [NII]/H$\alpha$ and [OI]/H$\alpha$) with increasing H$\alpha$ surface brightness (${\Sigma }_{H\alpha }$). 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 galaxies; (2) the observed trends of a flat or decreasing [OIII]/H$\beta$ with ${\Sigma }_{H\alpha }$; and (3) the offset of some DIG regions from the locus of HII 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$\alpha$ emission), but their harder spectra make them fundamental contributors to [OIII] 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.

accepted by A&A, posting version after proof corrections

References in corpus (45)

• The Host Galaxies and Classification of Active Galactic Nuclei
• The propagation of uncertainties in stellar population synthesis modeling I: The relevance of uncertain aspects of stellar evolution and the IMF to the derived physical properties of galaxies
• Overview of the SDSS-IV MaNGA Survey: Mapping Nearby Galaxies at Apache Point Observatory
• Improving the full spectrum fitting method: accurate convolution with Gauss-Hermite functions
• HyperLEDA. III. The catalogue of extragalactic distances
• The MAPPINGS III Library of Fast Radiative Shock Models
• The MUSE second-generation VLT instrument
• UV-extended E-MILES stellar population models: young components in massive early-type galaxies
• The Data Processing Pipeline for the MUSE Instrument
• The MUSE Hubble Ultra Deep Field Survey: I. Survey description, data reduction and source detection
• The Vertical Structure of Warm Ionised Gas in the Milky Way
• A z=0 Multi-wavelength Galaxy Synthesis I: A WISE and GALEX Atlas of Local Galaxies
• The lifecycle of molecular clouds in nearby star-forming disc galaxies
• Fast and inefficient star formation due to short-lived molecular clouds and rapid feedback
• The PHANGS-MUSE survey -- Probing the chemo-dynamical evolution of disc galaxies
• SDSS-IV MaNGA: The Impact of Diffuse Ionized Gas on Emission-line Ratios, Interpretation of Diagnostic Diagrams, and Gas Metallicity Measurements
• Metallicity gradients in local field star-forming galaxies: Insights on inflows, outflows, and the coevolution of gas, stars and metals
• Distances to PHANGS Galaxies: New Tip of the Red Giant Branch Measurements and Adopted Distances
• 3D Turbulent Reconnection: Theory, Tests and Astrophysical Implications
• A Galactic-scale gas wave in the Solar Neighborhood
• Mapping metallicity variations across nearby galaxy disks
• A nearby M star with three transiting super-Earths discovered by K2
• PHANGS CO kinematics: disk orientations and rotation curves at 150 pc resolution
• Molecular Gas Properties on Cloud Scales Across the Local Star-forming Galaxy Population
• Diffuse ionized gas in galaxies across the Hubble sequence at the CALIFA resolution
• Stellar structures, molecular gas, and star formation across the PHANGS sample of nearby galaxies
• The interplay between a galactic bar and a supermassive black hole: nuclear fueling in a sub-parsec resolution galaxy simulation
• IZI: Inferring the Gas Phase Metallicity (Z) and Ionization Parameter (q) of Ionized Nebulae using Bayesian Statistics
• Gas flow in barred potentials
• SDSS IV MaNGA - The spatially resolved transition from star formation to quiescence
• Biases in metallicity measurements from global galaxy spectra: the effects of flux-weighting and diffuse ionized gas contamination
• Convection Causes Enhanced Magnetic Turbulence in Accretion Disks in Outburst
• The Gas-Star Formation Cycle in Nearby Star-Forming Galaxies I. Assessment of Multi-scale Variations
• The Effects of Diffuse Ionized Gas and Spatial Resolution on Metallicity Gradients: TYPHOON Two-Dimensional Spectrophotometry of M83
• Measuring the mixing scale of the ISM within nearby spiral galaxies
• SDSS-IV MaNGA: Refining Strong Line Diagnostic Classifications Using Spatially Resolved Gas Dynamics
• Which feedback mechanisms dominate in the high-pressure environment of the Central Molecular Zone?
• Evolution of Stellar Feedback in HII Regions
• Self-consistent predictions for LIER-like emission lines from post-AGB stars
• Diffuse Ionized Gas in Simulations of Multiphase, Star-Forming Galactic Disks
• SDSS IV MaNGA: Deep observations of extra-planar, diffuse ionized gas around late-type galaxies from stacked IFU spectra
• The MUSE Atlas of Disks (MAD): Ionized gas kinematic maps and an application to Diffuse Ionized Gas
• Models of Diffuse Hα in the Interstellar Medium: The Relative Contributions from In Situ Ionisation and Dust Scattering
• The post-maximum behaviour of the changing-look Seyfert galaxy NGC 1566
• Detection of Extraplanar Diffuse Ionized Gas in M83

Cited by in corpus (62)

• The PHANGS-MUSE survey -- Probing the chemo-dynamical evolution of disc galaxies
• Star Formation Laws and Efficiencies across 80 Nearby Galaxies
• The PHANGS-MUSE Nebula Catalogue
• H-alpha emission in local galaxies: star formation, time variability and the diffuse ionized gas
• Environmental dependence of the molecular cloud lifecycle in 54 main sequence galaxies
• PHANGS-JWST First Results: A statistical view on bubble evolution in NGC628
• PHANGS-JWST First Results: Destruction of the PAH molecules in HII regions probed by JWST and MUSE
• PHANGS-JWST First Results: Mid-infrared emission traces both gas column density and heating at 100 pc scales
• The physics of Lyman-alpha escape from disc-like galaxies
• The metallicity's fundamental dependence on both local and global galactic quantities
• The Physical Drivers and Observational Tracers of CO-to-H2 Conversion Factor Variations in Nearby Barred Galaxy Centers
• Stellar feedback in M83 as observed with MUSE -- II. Analysis of the HII region population: ionisation budget and pre-SN feedback
• PHANGS-JWST First Results: Rapid Evolution of Star Formation in the Central Molecular Gas Ring of NGC1365
• Calibration of hybrid resolved star formation rate recipes based on PHANGS-MUSE H$\alpha$ and H$\beta$ maps
• Inferring the HII region escape fraction of ionizing photons from infrared emission lines in metal-poor star-forming dwarf galaxies
• PHANGS-MUSE: Detection and Bayesian classification of ~40000 ionised nebulae in nearby spiral galaxies
• Variations in the ${\Sigma }_{\mathrm{SFR}}-{\Sigma }_{\mathrm{mol}}-{\Sigma }_{\star }$ plane across galactic environments in PHANGS galaxies
• SPICE: the connection between cosmic reionisation and stellar feedback in the first galaxies
• Calibrating mid-infrared emission as a tracer of obscured star formation on HII-region scales in the era of JWST
• ELVES III: Environmental Quenching by Milky Way-Mass Hosts
• Correlation between the gas-phase metallicity and ionization parameter in extragalactic HII regions
• A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE).XIV. The main sequence relation in a rich environment down to M_star ~ 10^6 Mo
• Stellar associations powering HII regions $\unicode{x2013}$ I. Defining an evolutionary sequence
• Quantifying the energy balance between the turbulent ionised gas and young stars
• Stellar feedback in M83 as observed with MUSE -- I. Overview, an unprecedented view of the stellar and gas kinematics and evidence of outflowing gas
• Detection of He++ ion in the star-forming ring of the Cartwheel using MUSE data and ionizing mechanisms
• Metallicity calibrations based on auroral lines from PHANGS-MUSE data
• The PHANGS-HST-Halpha Survey: Warm Ionized Gas Physics at High Angular resolution in Nearby GalaxieS with the Hubble Space Telescope
• The MUSE view of ram pressure stripped galaxies in clusters: the GASP sample
• JWST MIRI and NIRCam observations of NGC 891 and its circumgalactic medium
• Empirical SED Templates for Star Clusters Observed with HST and JWST: No Strong PAH or IR Dust Emission after Five Myr
• The THESAN-ZOOM project: central starbursts and inside-out quenching govern galaxy sizes in the early Universe
• Physical Conditions and Extension of the Coronal Line Region in IC 5063
• A physically motivated `charge-exchange method' for measuring electron temperatures within HII regions
• Linking stellar populations to HII regions across nearby galaxies. II. Infrared Reprocessed and UV Direct Radiation Pressure in HII Regions
• MUSE crowded field 3D spectroscopy in NGC 300 III. Characterizing extremely faint HII regions and diffuse ionized gas
• Machine learning the gap between real and simulated nebulae: A domain-adaptation approach to classify ionised nebulae in nearby galaxies
• Warm ionized gas in the blue compact galaxy Haro 14 viewed by MUSE. The diverse ionization mechanisms acting in low-mass starbursts
• Constraining the LyC escape fraction from LEGUS star clusters with SIGNALS HII region observations: A pilot study of NGC 628
• Polycyclic aromatic hydrocarbons destruction in star-forming regions across 42 nearby galaxies
• The need for multicomponent dust attenuation in modeling nebular emission: Constraints from SDSS-IV MaNGA
• The softness diagram for MaNGA star-forming regions: diffuse ionized gas contamination or local HOLMES predominance?
• Pre-supernova stellar feedback in nearby starburst dwarf galaxies
• On the limitations of H alpha luminosity as a star formation tracer in spatially resolved observations
• A sensitive, high-resolution, wide-field IRAM NOEMA CO(1-0) survey of the very nearby spiral galaxy IC 342
• Bidimensional Exploration of the warm-Temperature Ionised gaS (BETIS) II. Revisiting the ionisation mechanism of the extraplanar diffuse ionised gas
• A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) XVII. Statistical properties of individual HII regions in unperturbed systems
• Bidimensional Exploration of the warm-Temperature Ionised gaS (BETIS) I. Showcase sample and first results
• Duration and properties of the embedded phase of star formation in 37 nearby galaxies from PHANGS-JWST
• Measuring 60-pc-scale Star Formation Rate of the Nearby Seyfert Galaxy NGC 1068 with ALMA, HST, VLT/MUSE, and VLA
• Unveiling the gravitationally unstable disc of a massive star-forming galaxy using NOEMA and MUSE
• Beyond diagnostic-diagrams: A critical exploration on the classification of ionization processes
• Diffuse Ionized Gas in the Anti-center of the Milky Way
• The SAMI Survey: Evidence for dynamical coupling of ionised gas and young stellar populations
• The ALPINE-CRISTAL-JWST Survey: Gas-phase abundance gradients of main sequence star-forming galaxies and their kinematics at $4<z<6$
• Spatially-resolved Galactic HII regions observed by LAMOST medium-Resolution Spectroscopic Survey of Nebulae (LAMOST MRS-N)
• M^3D: Mosaicking M33 with MUSE datacubes I. Unveiling the diversity of HII regions in M33 with MUSE
• The impact of bars on the properties of HII regions in the TIMER survey
• PHANGS-MUSE: the HII region luminosity function of local star-forming galaxies
• Stellar associations powering HII regions $\unicode{x2013}$ II. Escape fraction of ionizing photons
• Nebular abundance gradient in the Cartwheel galaxy using MUSE data
• Resolved molecular gas and star-formation in massive unquenched spirals : I. UGC 8179