The Abundance Gradient in the Extremely Faint Outer Disk of NGC 300

Abstract

In an earlier work, we showed for the first time that the resolved stellar disk of NGC 300 is very extended with no evidence for truncation, a phenomenon that has since been observed in other disk galaxies. We revisit the outer disk of NGC 300 in order to determine the metallicity of the faint stellar population. With the Gemini Multi Object Spectrograph camera at Gemini South, we reach 50% completeness at (g′, i′) = (26.8-27.4, 26.1-27.0) in photometric conditions and 07 seeing. At these faint depths, careful consideration must be given to the background galaxy population. The mean colors of the outer disk stars fall within the spread of colors for the background galaxies, but the stellar density dominates the background galaxies by 2:1. The predominantly old stellar population in the outer disk exhibits a negative abundance gradient - as expected from models of galaxy evolution - out to about 10 kpc where the abundance trend changes sign. We present two scenarios to explain the flattening, or upturn, in the metallicity gradient of NGC 300 and discuss the implication this has for the broader picture of galaxy formation. Show more