其他摘要 | Understanding the formation and evolution of galaxies is one of the most importantquestions in cosmology. With increases in telescope size and proved instruments, we can obtain multiband photometric and high-resolution spectroscopic data of extragalactic data. It is possible to take advantage of these data to study the properties of galaxies to an ever greater extent. Evolutionary population synthesis (EPS) is one of the methods used to study the properties of galaxies. People can build the EPS models based on the stellar evolution theory, stellar spectral library and the assumption of stellar initial mass function. The stellar masses, mean ages, metallicites and star formation histories of galaxies can be obtained via fitting the observations of galaxies to the EPS models. We can also use EPS to study the structure and evolution of galaxies. Based on the EPS models, there have three very common methods used in the galaxy studies, namely color, Lick-index and spectrum-fitting methods. It is very important to test and estimate the reliability of these methods, especially because many extragalactic studies are heavily dependent on them. Galactic globular clusters provide an excellent medium for such test, because they can be considered as simple stellar populations. We present ages and metallicities for 40 globular clusters as determined from these three methods based on the Bruzual & Charlot EPS models. By comparing with the ages obtained from color-magnitude diagrams and metallicities obtained from the spectra of stars, we are able to estimate the ability of these methods to determination parameters. As a result, we find that: (i) for the metallicity, our derived metallicities agree with those derived from the spectra of stars, Lick-index method is suitable to study metallicity for the stellar population systems in the range of −1.5 .[Fe/H]. −0.7 and spectrum-fitting method is suitable to study metallicity for the stellar population systems in the range of −2.3 .[Fe/H]. −1.5; (ii) for the age, these three methods have difficulties in age determination, our derived ages are smaller (about 2.0 Gyr, on average) than the results of CMDs for all these three methods. We use Vazdekis and Maraston models to analyze whether our results are dependent on EPS models, and find that the tendency of these two models is the same as that of Bruzual & Charlot models. Our results are independent of the EPS models. Besides the age-metallicity degeneracy, we examine the possible effects of other factors (horizontal branch morphology, blue straggler stars, binary interactions and α−enhancement) and give quantitative analysis of the influences of these factors on age determinations. People can study the stellar masses, mean ages, metallicites and star formation histories of galaxies via fitting the observations of galaxies to the EPS models, and the EPS models play an important role in such studies. The binary stars can significantly affect the ultraviolet (UV) spectra of intermediate-age (∼ 1.0 Gyr) stellar populations. Binary stars are very common in the Universe, hence binary stars are important for the optical (observed frame) colors for galaxies at z∼ 2.0, when the rest frame UV emission is shifted to optical passbands. We use the Monte Carlo method to simulate the galaxy sample with different redshift and morphology based on two different EPS models (Yunnan-ssp and Yunnan-bsp). We present the magnitudes and colors in observed frame for galaxies with star formation rate described by three forms, and we divide our galaxy sample into two sample to study the influence of binary stars on the magnitudes and colors for galaxies, one is with short star formation time scale, and the other is with long star formation time scale. We find the binary stars can alter the magnitudes and colors for the galaxies with short star formation time scale, binary stars can make the g band bluer about 1.5mag, g − r bluer about 1.0mag, u − g redder about 1.5mag. |
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