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Using colours to determine the stellar ages and metallicities of distant galaxies

The determination of stellar populations of galaxies are important for studying the formation and evolution of galaxies, because all galaxies contain many stars and they evolve with galaxies. Spectra data are usually used to determine the stellar populations of nearby galaxies as they have the ability to disentangle the degeneracy between stellar age and metallicity. However, it is difficult to give similar studies to distant (e.g., $z >$ 0.3) galaxies because of the lack of reliable spectra data. This is actually limited by current observational equipments and methods. In fact, the information of the stellar ages and metallicities of distant galaxies are crucial for solving the problem of galaxy formation and evolution. Colours can give us some information of the stellar populations of distant galaxies. In the paper, I introduce our works about using colours to estimate the ages and metallicities of the stellar populations of galaxies. Some potential colours for studying stellar-population parameters (age and metallicity) and their sensitivities to stellar-population parameters are reviewed. A new composite stellar population model that includes both single stars and binary stars is also introduced.