PPAK Wide-field Integral Field Spectroscopy of NGC 628: II. Emission line abundance analysis

TL;DR

This paper presents a detailed 2D emission line abundance analysis of NGC 628 using PPAK IFS data, revealing complex metallicity gradients, spatial variations, and metal-rich regions, advancing understanding of galaxy chemical evolution.

Contribution

Introduces a comprehensive methodology for 2D abundance analysis with PPAK IFS data, providing the most complete metallicity gradient of NGC 628 and insights into its spatial chemical variations.

Findings

Identifies a multi-modality in the galaxy's abundance gradient.

Detects regions of metal enhancement with spatially varying properties.

Shows that metallicity scatter reflects true physical variation, not measurement errors.

Abstract

In this second paper of the series, we present the 2-dimensional (2D) emission line abundance analysis of NGC 628, the largest object within the PPAK Integral Field Spectroscopy (IFS) Nearby Galaxies Survey: PINGS. We introduce the methodology applied to the 2D IFS data in order to extract and deal with large spectral samples, from which a 2D abundance analysis can be later performed. We obtain the most complete and reliable abundance gradient of the galaxy up-to-date, by using the largest number of spectroscopic points sampled in the galaxy, and by comparing the statistical significance of different strong-line metallicity indicators. We find features not previously reported for this galaxy that imply a multi-modality of the abundance gradient consistent with a nearly flat-distribution in the innermost regions of the galaxy, a steep negative gradient along the disc and a shallow gradient or nearly-constant metallicity beyond the optical edge of the galaxy. The N/O ratio seems to follow the same radial behaviour. We demonstrate that the observed dispersion in metallicity shows no systematic dependence with the spatial position, signal-to-noise or ionization conditions, implying that the scatter in abundance for a given radius is reflecting a true spatial physical variation of the oxygen content. Furthermore, by exploiting the 2D IFS data, we were able to construct the 2D metallicity structure of the galaxy, detecting regions of metal enhancement, and showing that they vary depending on the choice of the metallicity estimator. The analysis of axisymmetric variations in the disc of NGC 628 suggest that the physical conditions and the star formation history of different-symmetric regions of the galaxy have evolved in a different manner.