Stellar Populations in Gas-rich Galaxy Mergers. II. Feedback Effects of Type IA and Type II Supernovae

Kenji Bekki, Yasuhiro Shioya

Research output: Contribution to journalArticle

Abstract

We numerically investigate the chemodynamical evolution of major disk- disk galaxy mergers in order to explore the origin of mass-dependent chemical, photometric, and spectroscopic properties observed in elliptical galaxies. We particularly investigate the dependence of the fundamental properties on the merger progenitor-disk mass (Md). The main results obtained in this study 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 ~1.0 solar abundance (Z~0.02) for ellipticals formed by mergers with Md=1010 Msolar to ~2.0 solar (Z~0.04) for those with Md=1012 Msolar. (2) The absolute magnitude of negative metallicity 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 to be larger for more massive ellipticals, which reflects the fact that the metallicity gradient is larger for more massive ellipticals. For example, the typical U-R color gradient (∆U-R/∆logR) for 0.1<=R/Re<=1.0 is -0.13 for ellipticals with Md=1012 Msolar and -0.07 for those with Md=1010 Msolar. (4) Both the Mg2 line index in the central parts of ellipticals (R<=0.1Re) and the radial Mg2 gradient (∆Mg2/∆logR) are more likely to be larger for massive ellipticals. ∆Mg2/∆logR correlates reasonably well with the central Mg2 in ellipticals. For most of the present merger models, ellipticals show positive radial gradients of the Hβ line index. (5) Both M/LB and M/LK, where M, LB, and LK are the total stellar mass of galaxy mergers and the B- and K-band luminosities, respectively, depend on galactic mass in such a way that more massive ellipticals have larger M/LB and smaller M/LK. The essential reason for the mass dependence of the derived chemical, photometric, and spectroscopic properties of ellipticals 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 greatly affect the chemodynamical evolution of galaxy mergers.
Original languageEnglish
Pages (from-to)108-127
Number of pages20
JournalThe Astrophysical Journal
Volume513
Publication statusPublished - 1999

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