Metallicity Structure in the Milky Way Disk Revealed by Galactic HII Regions

Abstract

The metallicity structure of the Milky Way disk stems from the chemodynamical evolutionary history of the Galaxy. We use the National Radio Astronomy Observatory Karl G. Jansky Very Large Array to observe ~8-10 GHz hydrogen radio recombination line and radio continuum emission toward 82 Galactic HII regions. We use these data to derive the electron temperatures and metallicities for these nebulae. Since collisionally excited lines from metals (e.g., oxygen, nitrogen) are the dominant cooling mechanism in HII regions, the nebular metallicity can be inferred from the electron temperature. Including previous single dish studies, there are now 167 nebulae with radio-determined electron temperature and either parallax or kinematic distance determinations. The interferometric electron temperatures are systematically 10% larger than those found in previous single dish studies, likely due to incorrect data analysis strategies, optical depth effects, and/or the observation of different gas by the interferometer. By combining the interferometer and single dish samples, we find an oxygen abundance gradient across the Milky Way disk with a slope of -0.052 +/- 0.004 dex/kpc. We also find significant azimuthal structure in the metallicity distribution. The slope of the oxygen gradient varies by a factor of ~2 when Galactocentric azimuths near 30 deg are compared with those near 100 deg. This azimuthal structure is consistent with simulations of Galactic chemodynamical evolution influenced by spiral arms.

51 pages, 16 figures, 7 tables, 1 appendix; accepted for publication in ApJ

References in corpus (19)

• The NumPy array: a structure for efficient numerical computation
• The distance to the Orion Nebula
• Kinematic Distances to Molecular Clouds identified in the Galactic Ring Survey
• The APOGEE red-clump catalog: Precise distances, velocities, and high-resolution elemental abundances over a large area of the Milky Way's disk
• Water maser motions in W3(OH) and a determination of its distance
• Reconstructing the star formation history of the Milky Way disc(s) from chemical abundances
• The Electron Temperature Gradient in the Galactic Disk
• A Parallactic Distance of 389 +24/-21 parsecs to the Orion Nebula Cluster from Very Long Baseline Array Observations
• Trigonometric parallaxes of star forming regions in the Sagittarius spiral arm
• Trigonometric Parallaxes of Star Forming Regions in the Perseus Spiral Arm
• Trigonometric Parallaxes of Massive Star Forming Regions: V. G23.01-0.41 and G23.44-0.18
• Radio Recombination Lines in Galactic HII Regions
• The Chemical Evolution Carousel of Spiral Galaxies: Azimuthal Variations of Oxygen Abundance in NGC1365
• Trigonometric Parallaxes of Star Forming Regions in the Scutum Spiral Arm
• Parallaxes of Star Forming Regions in the Outer Spiral Arm of the Milky Way
• Oxygen abundance distribution in Galactic disc
• Chemical distribution of HII regions towards the Galactic anticentre
• Arm and interarm abundance gradients in CALIFA spiral galaxies
• The Southern HII Region Discovery Survey I: The Bright Catalog

Cited by in corpus (46)

• The GALAH survey: tracing the Galactic disk with Open Clusters
• A Tale of Two Disks: Mapping the Milky Way with the Final Data Release of APOGEE
• Spectroscopic age estimates for APOGEE red-giant stars: Precise spatial and kinematic trends with age in the Galactic disc
• Gradients of chemical abundances in the Milky Way from HII regions: distances derived from Gaia EDR3 parallaxes and temperature inhomogeneities
• 3-D gas-phase elemental abundances across the formation histories of Milky Way-mass galaxies in the FIRE simulations: initial conditions for chemical tagging
• The Mass-Size Relation and the Constancy of GMC Surface Densities in the Milky Way
• Quantifying radial migration in the Milky Way: Inefficient over short timescales but essential to the very outer disc beyond ~15 kpc
• The homogeneity of the star forming environment of the Milky Way disk over time
• The detection of a hot molecular core in the extreme outer Galaxy
• Slow Star Formation in the Milky Way: Theory Meets Observations
• The GALAH Survey: Chemical Clocks
• Migration and Mixing in the Galactic Disc from Encounters between Sagittarius and the Milky Way
• The GBT Diffuse Ionized Gas Survey (GDIGS): Survey Overview and First Data Release
• GASKAP Pilot Survey Science II: ASKAP Zoom Observations of Galactic 21-cm Absorption
• The Southern HII Region Discovery Survey. II. The Full Catalog
• The Gaia-ESO Survey: Oxygen abundance in the Galactic thin and thick disks
• A multiwavelength study of the W33 Main ultracompact HII region
• 2D chemical evolution models II. Effects of multiple spiral arm patterns on O, Eu, Fe and Ba abundance gradients
• A global view on star formation: The GLOSTAR Galactic plane survey X. Galactic HII region catalog using radio recombination lines
• A physically motivated `charge-exchange method' for measuring electron temperatures within HII regions
• Caught in the Act: A Metal-Rich High-Velocity Cloud in the Inner Galaxy
• CHEMOUT: CHEMical complexity in star-forming regions of the OUTer Galaxy. II. Methanol formation at low metallicity
• Parallax-based Distances to Galactic Hii Regions: Nearby Spiral Structure
• Constraints on the history of Galactic spiral arms revealed by Gaia GSP-Spec alpha-elements
• Surveying the Giant HII Regions of the Milky Way with SOFIA: IV. Sgr D, W42, and a Reassessment of the Giant HII Region Census
• Chemodynamic evolution of Sun-like stars in nearby moving groups
• Green Bank Telescope Observations of ${}^3\mathbf{H}{\mathbf{e}}^{+}$: Planetary Nebulae
• Probing the strength of radial migration via churning by using metal-rich red giant stars from APOGEE
• Overview Results of JWST Observations of Star-Forming Clusters in the Extreme Outer Galaxy
• Effects of secular growth and mergers on the evolution of metallicity gradients and azimuthal variations in a Milky Way-like galaxy
• Do All Low-Mass Stars Undergo Extra Mixing Processes?
• Discovery of Hydrogen Radio Recombination Lines at z=0.89 towards PKS 1830-211
• Discovery of a New Population of Galactic HII Regions with Ionized Gas Velocity Gradients
• 3D structure of HII regions in the star-forming complex S254-S258
• Diffuse Ionized Gas in the Anti-center of the Milky Way
• Hot accretion onto spiral galaxies: the origin of extended and warped HI discs
• A Complete X-ray View of Supernova Remnant W28 with Einstein Probe: Spatial Distribution of Parameters and Origin of the Thermal-Composite Morphology
• Molecular Clouds at the Edge of the Galaxy I. Variation of CO J=2-1/1-0 Line Ratio
• A comparative study of O, Ne, Cl, and Ar in Hii regions and PNe of the Galactic disk: Temporal evolution of radial gradients?
• Chemistry of Dark Molecular Clouds
• A VLA Census of the Galactic H II Region Population
• A global view on star formation: The GLOSTAR Galactic plane survey XII. Effelsberg's continuum view and data release
• Metallicity Structure in Galactic Longitude-Velocity Diagrams of the Milky Way Disk and FIRE-2 Simulations
• 3D elemental abundances of stars at formation across the histories of Milky Way-mass galaxies in the FIRE simulations
• SDSS-V LVM: Verifying what, and where, the 'Galactic Center' Lobe is
• The MAGIC project. III. Radial and azimuthal Galactic abundance gradients using classical Cepheids