A comparative study of O, Ne, Cl, and Ar in H
ii
regions and PNe of the Galactic disk: Temporal evolution of radial gradients?
A Amayo, L Carigi, J E Méndez-Delgado, J García-Rojas, E Reyes-Rodríguez Abstract
We compare the radial abundance gradients of O, Ne, Cl, and Ar using a sample of 42 H ii regions and 176 planetary nebulae (PNe) from the DESIRED catalogue in the Galactic disk. Both samples comprise the highest-quality observations currently available. Actually, this work presents the first gradient analysis for the DESIRED dataset. For all objects, two sets of chemical abundances were compiled: one derived from collisionally excited lines (CELs) and another incorporating the temperature fluctuation parameter (t2). Oxygen abundances were corrected for dust depletion, and the results for H ii regions were compared with those of Cepheid stars, which trace the present-day interstellar medium. Distances for PNe were carefully compiled from the most recent literature, excluding objects associated with the bulge or halo to ensure a disk-only sample. All gradients are statistically significant (p-values <0.05), except for Cl and Ar in H ii regions. The O/H gradients derived from H ii regions and Cepheids are consistent when t2 is included, underscoring the importance of accounting for temperature inhomogeneities in nebular analyses. The O and Ne gradients traced by older objects are flatter than the present-day gradient by −0.028 ± 0.008 dex kpc−1 on average, from both RLs and CELs. This could be interpreted as a temporal steepening of the Galactic abundance gradient in ISM; however, such behaviour is not reproduced by several chemical evolution models, suggesting that additional physical processes could be influencing the observed trends. The most plausible explanation is that our PNe sample has been strongly affected by radial migration. Under this interpretation, the PNe gradient cannot reliably trace past abundance gradients, but it provides a valuable constraint on radial stellar migration, offering important input for chemo-dynamical models of the Galactic disk and for hydrodynamical simulations.