Clues on the rejuvenation of the S0 galaxy NGC 404 from the chemical abundance of its outer disk

TL;DR

This study measures the oxygen abundance in NGC 404's outer disk, revealing high metallicity that challenges cold accretion and merger scenarios, and suggests recent star formation is a declining remnant of the galaxy's original activity.

Contribution

It provides the first detailed chemical abundance measurement of NGC 404's outer disk, offering new insights into its star formation history and galaxy assembly processes.

Findings

Oxygen abundance is about 80% of solar value.

High metallicity challenges cold accretion and merger models.

Recent star formation is likely a declining remnant of past activity.

Abstract

The oxygen abundance of the outer disk of the nearby S0 galaxy NGC 404, a prototypical early-type galaxy with extended star formation, has been derived from the analysis of HII region spectra. The high mean value found, 12+log(O/H)=8.6 \pm 0.1, equivalent to approximately 80% of the solar value, argues against both the previously proposed cold accretion and recent merger scenarios as viable mechanisms for the assembly of the star-forming gas. The combination of the present-day gas metallicity with the published star formation history of this galaxy favors a model in which the recent star forming activity represents the declining tail of the original one.