SDSS-IV MaNGA: Environmental Dependence of the Mgb/${\\boldsymbol{\\langle }}{\\bf{Fe}}{\\boldsymbol{\\rangle }}$–${{\\boldsymbol{\\sigma }}}_{{\\boldsymbol{* }}}$ 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/á ñ Fe 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 (zf). We find that (1) all galaxies show a tight correlation between Mgb/á ñ Fe and * s ; (2) “old” (Hβ< 3) low-σ* galaxies in high local density environment and inner regions within galaxy groups are enhanced in Mgb/á ñ Fe , while “young” (Hβ> 3) galaxies and high-mass galaxies show no or less environmental dependence; (3) “old” galaxies with high-zf show enhanced Mgb/á ñ Fe over lowand medium-zf; and (4)Mgb/á ñ Fe gradients are close to zero and show dependence on σ* but no obvious dependence on the environment or zf. Our study indicates that stellar velocity dispersion or galaxy mass is the main parameter driving the Mgb/á ñ Fe enhancement, although environments appear to have modest effects, particularly for lowand medium-mass galaxies.