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

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• The GALAH survey: tracing the Galactic disk with Open Clusters
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• Quantifying radial migration in the Milky Way: Inefficient over short timescales but essential to the very outer disc beyond ~15 kpc
• Slow Star Formation in the Milky Way: Theory Meets Observations
• The Gaia-ESO Survey: Oxygen abundance in the Galactic thin and thick disks
• Green Bank Telescope Observations of ${}^3\mathbf{H}{\mathbf{e}}^{+}$: Planetary Nebulae
• A VLA Census of the Galactic H II Region Population