SDSS-IV MaNGA: Environmental dependence of the Mgb/<Fe>-sigma* relation for nearby galaxies
Abstract
We use a sample of ~3000 galaxies from the MaNGA MPL-7 internal data release to study the alpha abundance distribution within low-redshift galaxies. We use the Lick index ratio Mgb/<Fe> as an alpha abundance indicator to study relationships between the alpha abundance distribution and galaxy properties such as effective stellar velocity dispersion within 0.3 effective radii (sigma*), galaxy environment, and dark matter halo formation time (zf). We find that (1) all galaxies show a tight correlation between Mgb/<Fe> and sigma*; (2) `old' (Hbeta < 3) low-sigma* galaxies in high local density environment and inner regions within galaxy groups are enhanced in Mgb/<Fe>, while `young' (Hbeta>3) galaxies and high-mass galaxies show no or less environmental dependence; (3) `old' galaxies with high-zf show enhanced Mgb/<Fe> over low- and medium-zf; (4) Mgb/<Fe> gradients are close to zero and show dependence on sigma* 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/<Fe> enhancement, although environments appear to have modest effects, particularly for low- and medium-mass galaxies.
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