Chemical Evolution of Gas-Rich Galaxy Mergers

Abstract

We investigate numerically the chemodynamical evolution of major disc–disc galaxy mergers in order to explore the origin of the mass-dependent chemical, photometric and spectroscopic properties observed in elliptical galaxies. We investigate especially the dependence of the fundamental properties on merger progenitor disc mass (Md). Three main results are obtained in this study:– More massive (luminous) ellipticals formed by galaxy mergers between more massive spirals have higher metallicity (Z) and thus show redder colours; the typical metallicity ranges from ∼ 1.0 solar abundance (Z∼ 0.02) for ellipticals formed by mergers with Md = 1010M⊙to ∼ 2.0 solar (Z∼ 0.04) for those with Md= 1012M⊙.– Both the Mg2 line index in the central part of ellipticals (R ≤ 0.1 Re) and the radial gradient of Mg2 (δ Mg2 / δ log R) are more likely to be larger for massive ellipticals. δ Mg2 / δ log R correlates reasonably well with the central Mg2 in ellipticals. For most of the present merger models, ellipticals show a positive radial gradient of the Hβ line index. – Both M/LB and M/LK (where M, LB, and LK are the total stellar mass of galaxy mergers, the B-band and the K-band luminosities, respectively) depend on galactic mass in such a way that more massive ellipticals have larger M/LB and smaller M/LK.