Analysis of the Internal Radial Gradient of Chemical Abundances in Spiral Galaxies from CALIFA

Abstract The study of chemical evolution is of paramount importance for understanding the evolution of galaxies. Models and observations propose an inside-out mechanism in the formation of spiral galaxy disks, implying a negative radial gradient of elemental abundances when represented on a logarithmic scale. However, in some instances, the observed chemical abundance gradients deviate from a single negative straight line, revealing inner drops or outer flattenings, particularly in more massive galaxies. This study analyzes oxygen abundance gradients in spiral galaxies based on observations from the Calar Alto Legacy Integral Field Area survey. Our focus is specifically on examining oxygen abundance gradient profiles, as obtained with data from H ii regions, with a special emphasis on the inner radial gradient. We employ an automated fitting procedure to establish correlations between the physical properties of galaxies and bulges and the presence of these inner drops, seeking potential explanations for these variations in gradient. We find that the different criteria used in the literature to distinguish H ii regions from other ionization sources in the galaxies, such as active galactic nuclei, significantly impact the results, potentially altering abundance gradient profiles and uncovering galaxies with distinct inner drops. Additionally, we analyze the abundance radial gradients to investigate the impact of diffuse ionized gas (DIG) decontamination on oxygen abundances over these inner drops. We observe that DIG, concentrated mainly in the central regions of galaxies, can modify oxygen abundance gradient profiles if left unaddressed.