| Research Abstract |
We have studied the formation and evolution of elliptical galaxies by analysing the nature of stellar populations and the hot X-ray gas in and around elliptical galaxies as well as the characteristics of globular cluster systems around galaxies. 1 First, we have built a new chemical and spectral evolution model for galaxies of any star formation history. 2 By appling this model to the luminosity and color function of globular clusters around elliptical galaxies in Virgo cluster, we find that these cluster formed about 12-18 Gyrs ago in 2-3 Gyrs. 2 Next, we have compiled the spectral energy distribution data of radio-selected elliptical galaxies, and find that galaxies at z >= 2 show a conspicuous evidence for large scale star formation, while those nearer do not. 4 We have taken spectra of 28 bulges of spiral galaxies and convincingly show that the luminosity-metallicity relation of bulges is identical to that of elliptical galaxies. 2-4 strongly suggest that formation of elliptical ga
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laxies was dominated by protogalactic collapse and dissipational star formation early in the evolution of the universe. 5 The iron abundance of the hot X-ray gas around elliptical galaxies should be at least equal to or even more than the mean stellar iron abundance of ellipticals, and yet we have obtained much lower iron abundances by using ASCA X-ray satelite. Through a detailed investigation based on our knowledges on astrophysics, we reach to a conclusion that there must be something wrong in the fundamental atomic physics data of iron L-lines in the plasma code used for data reduction. 6 We have carefully re-estimated the relative abundance ratios of elements in the intracluster medium, by correctly using the solar meteoritic iron abundance, and find that the origin of iron in the ICM should be mainly in type Ia supernovae and not in type II,contrary to the recent claims in the literature. 5-6 give another support from chemical evolution approach to the conclusion reached by 2-4. Finally, we believe it is of prime importance to detect directly elliptical galaxies at star formation epoch, which could be best detected in CO luminosity peak. 7 To involve the evolution of CO luminosity in our model, we study the spatial distribution of CO and HI gas in disk galaxies and obtain the conversion factor from CO to H2 molecules that is inversely proportinal to the gas metallicity. This new knowledge could be applied to our next step for a search of star forming ellipticals by CO radio observation. Less
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