An estimate of the time variation of the O/H radial gradient from planetary nebulae

Abstract

Abstract. Radial abundance gradients are a common feature of spiral galaxies, and in the case of the Galaxy both the magnitude of the gradients and their variations are among the most important constraints of chemical evolution models. Planetary nebulae (PN) are particularly interesting objects to study the gradients and their variations. Owing to their bright emission spectra, they can be observed even at large galactocentric distances, and the derived abundances are relatively accurate, with uncertainties of about 0.1 to 0.2 dex, particularly for the elements that are not synthesized in their progenitor stars. On the other hand, as the offspring of intermediate mass stars, with main sequence masses in the interval of 1 to 8 solar masses, they are representative of objects with a reasonable age span. In this paper, we present an estimate of the time variation of the O/H radial gradient in a sample containing over 200 nebulae with accurate abundances. Our results are consistent with a flattening of the O/H gradient roughly from −0.11 dex/kpc to −0.06 dex/kpc during the last 9 Gyr, or from −0.08 dex/kpc to −0.06 dex/kpc during the last 5 Gyr.

Mild evolution of the stellar metallicity gradients of disc galaxies

“…From those metallicity gradients, it is possible to infer the level of evolution, assuming stars do not strongly modify their spatial locations after their birth. For the MW, Maciel et al (2003) estimated a weak evolution consistent with the metallicity gradients to be more negative in the past. Recent estimations by Magrini et al (2016) for galaxies in the Local Group suggest no evolution since z ∼ 0.5.…”

“…Maciel et al 2003;Magrini et al 2016). From those metallicity gradients, it is possible to infer the level of evolution, assuming stars do not strongly modify their spatial locations after their birth.…”

“…We note that these are global trends and as can be seen from Table 1 Median slopes of the metallicity profiles for all simulated discs (black circles) and for those in the low-mass (red squares) and high-mass (blue diamonds) subsamples as a function of redshift. For comparison we include the observational estimations reported by Maciel et al (2003) for the Milky Way (green open circles) and by Magrini et al (2016) (orange stars) for nearby galaxies. Estimations of the median metallicity gradients (open triangles) performed using the ages and spatial distributions of stars at z ∼ 0 are included (see text for details).…”

“…Henry et al 2010;Stanghellini et al 2010). Maciel et al (2003) calculated the gradients of SPs with different ages in the Milky Way disc, finding a signal of increasingly negative metallicity gradients for older stars. Recently Magrini et al (2016) analysed the metallicity gradients determined by PN for four nearby galaxies, finding them to be flatter than those detected using HII regions.…”

The evolution of the oxygen abundance radial gradient in the Milky Way Galaxy disk

“…The PN are useful to estimate the radial gradient of Oxygen, an element not modified by the nucleosynthesis in the progenitors stars of PN. The early data analyzing this question Maciel, Costa & Uchida (2003) showed a radial gradient steeper than the one for the present time, although, due to error bars, the observational points mixed with the Hii regions data in the plot of O/H vs galactocentric radius R. The open clusters problems are derived of the necessary classification in thin or thick disk or even halo populations before their use in a radial distribution of metallicity. Furthermore, the ages determination, coming from a fit of their spectra to stellar models, which depend on metallicity and on age simultaneously, added to differences depending on the use of LTE or NLTE models, may be uncertain.…”