Stellar populations in gas-rich galaxy mergers. II. Feedback effects of type Ia and type II supernovae

We numerically investigate the chemodynamical evolution of major disk-disk galaxy mergers in order to explore the origin of mass-dependent chemical, p hotometric, and spectroscopic properties observed in elliptical galaxies. W e particularly investigate the dependence of the fundamental properties on the merger progenitor-disk mass (M-d). The main results obtained in this st udy are the following five. (1) More massive (luminous) ellipticals formed by galaxy mergers between more massive spirals have larger metallicities (Z ) and thus show redder colors. The typical metallicity ranges from similar to 1.0 solar abundance (Z similar to 0.02) for ellipticals formed by merger s with M-d = 10(10) M. to similar to 2.0 solar (Z similar to 0.04) for thos e with M-d similar to 10(12) M.. (2) The absolute magnitude of negative met allicity gradients developed in galaxy mergers is more likely to be larger for massive ellipticals. The absolute magnitude of the metallicity gradient correlates with that of the age gradient in ellipticals in the sense that an elliptical with steeper negative metallicity gradient is more likely to show a steeper age gradient. (3) The radial color gradient is more likely t o be larger for more massive ellipticals, which reflects the fact that the metallicity gradient is larger for more massive ellipticals. For example, t he typical U-R color gradient (Delta U-R/Delta log R) for 0.1 less than or equal to R/R-e less than or equal to 1.0 is -0.13 for ellipticals with M-d = 10(12) M. and -0.07 for those with M-d = 10(10) M.. (4) Both the Mg-2 lin e index in the central parts of ellipticals (R less than or equal to 0.1 R- e) and the radial Mg-2 gradient (Delta Mg-2/Delta log R) are more likely to be larger for massive ellipticals. Delta Mg-2/Delta log R correlates reaso nably well with the central Mg, in ellipticals. For most of the present mer ger models, ellipticals show positive radial gradients of the H beta line i ndex. (5) Both M/L-B and M/L-K, where M, L-B, and L-K are the total stellar mass of galaxy mergers and the B- and K-band luminosities, respectively, d epend on galactic mass in such a way that more massive ellipticals have lar ger M/L-B and smaller M/L-K. The essential reason for the mass dependence o f the derived chemical, photometric, and spectroscopic properties of ellipt icals is that galactic mass can largely determine the total amount of metal -enriched interstellar gas, the star formation histories of galaxy mergers, and the effectiveness of Type Ia and II supernova feedback, all of which g reatly affect the chemodynamical evolution of galaxy mergers.