SDSS-IV MaNGA: Environmental dependence of the Mgb/<Fe>-sigma_* relation for nearby galaxies

Zheng Zheng, Cheng Li, Shude Mao, Huiyuan Wang, Chao Liu, Houjun Mo, Zhen Yuan, Claudia Maraston, Daniel Thomas, Renbin Yan, Kevin Bundy, R. J. Long, Taniya Parikh, Grecco Oyarzun, Dmitry Bizyaev, Ivan Lacerna

Published 2019-02-20Version 1

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 (z_f). We find that (1) all galaxies show a tight correlation between Mgb/<Fe> and sigma_*; (2) `old' (H_beta < 3) low-sigma_* galaxies in high local density environment and inner regions within galaxy groups are enhanced in Mgb/<Fe>, while `young' (H_beta>3) galaxies and high-mass galaxies show no or less environmental dependence; (3) `old' galaxies with high-z_f show enhanced Mgb/<Fe> over low- and medium-z_f; (4) Mgb/<Fe> gradients are close to zero and show dependence on sigma_* 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/<Fe> enhancement, although environments appear to have modest effects, particularly for low- and medium-mass galaxies.