SDSS-IV MaNGA: Environmental Dependence of the Mgb/ – Relation for Nearby Galaxies

Abstract

We use a sample of ∼3000 galaxies from the MaNGA MPL-7 internal data release to study the α abundance distribution within low-redshift galaxies. We use the Lick index ratio Mgb/ as an α abundance indicator to study relationships between the α abundance distribution and galaxy properties such as effective stellar velocity dispersion within 0.3 effective radii ( σ * ), galaxy environment, and dark matter halo formation time ( z f ). We find that (1) all galaxies show a tight correlation between Mgb/ and (2) “old” (H β < 3) low- σ * galaxies in high local density environment and inner regions within galaxy groups are enhanced in Mgb/ , while “young” (H β > 3) galaxies and high-mass galaxies show no or less environmental dependence; (3) “old” galaxies with high- z f show enhanced Mgb/ over low- and medium- z f ; and (4) Mgb/ gradients are close to zero and show dependence on σ * but no obvious dependence on the environment or z f . Our study indicates that stellar velocity dispersion or galaxy mass is the main parameter driving the Mgb/ enhancement, although environments appear to have modest effects, particularly for low- and medium-mass galaxies.