Recalibration of the H$α$ surface brightness-radius relation for planetary nebulae using Gaia DR3: new distances and the Milky Way oxygen radial gradient

Abstract

The spatial distribution of chemical elements in the Galactic disk provides key constraints on models of galaxy evolution. However, studies using planetary nebulae (PNe) as tracers have been historically limited by large uncertainties in their distances. To overcome the long-standing distance uncertainties, we recalibrated the H$α$ surface brightness-radius relation from Frew et al. with Gaia DR3 parallaxes, deriving distances for 1,130 PNe of which 415 have Bayesian distances based on Gaia DR3 parallaxes. The O/H radial gradient for 231 disk PNe is fitted considering three models: a single linear gradient and segmented linear fits with one or two breaks. The segmented fits indicate a change in slope near the solar radius (R ~8 kpc), with a flatter or slightly positive gradient inward and a steeper negative gradient outward. This feature may reflect changes in star formation efficiency driven by the Galactic bar or the corotation resonance of the spiral arms. The breaks in the metallicity radial gradients observed in this work may result from the superposition of distinct stellar populations associated with the thin and thick disks. The two-dimensional O/H distribution in the Galactic plane supports the adopted distances and reveals modest azimuthal asymmetry, with enhanced abundances near the bar at positive longitudes, and a bimodal abundance structure between the inner and outer solar regions. Our results provide new constraints on the chemical evolution of the Milky Way, the impact of non-axisymmetric structures, and the possible existence of distinct radial abundance regimes across the Galactic disk.