We have analyzed the population of planetary nebulae in galaxies of the Local group, NGC3109, NGC6822, NGC300, M31 and others. In this work we will present the behavior of the chemical gradients in the disk galaxies M31, M33, NGC300 and the Milky Way, based on the analysis of the chemical composition of planetary nebulae (old population) and HII regions (young population). We will show that in all the cases the gradientes derived from planetary nebulae are flatter than the gradients shown by HII regions. The extreme case is M31, where the chemical abundances of planetary nebulae are not related to the galactocentric distances. Planetary nebulae in M31 show the same chemical abundances up to a galactocentric distance larger than 100 kpc. We will discuss possible causes for this phenomenon.
Enviado por miriam@astro.unam.mx, 2019 Oct