Old stellar population synthesis:new age and mass estimates for Mayall II = G1

作     者：Jun Ma Richard de Grijs Zhou Fan Soo-Chang Rey Zhen-Yu Wu Xu Zhou Jiang-Hua Wu Zhao-Ji Jiang Jian-Sheng Chen Kyungsook Lee Sangmo Tony Sohn 

作者机构：National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China Department of Physics ＆ Astronomy The University of Sheffield Hicks Building Hounsfield Road Sheffield S3 7RH UK Graduate University Chinese Academy of Sciences Beijing 100049 China Department of Astronomy and Space Science Chungnam National University Daejeon 305-764 Korea Center for Space Astrophysics Yonsei University Seoul 120-749 Korea California Institute of Technology MC 405-47 1200 E. California Boulevard Pasadena CA 91125 

出 版 物：《Research in Astronomy and Astrophysics》 (天文和天体物理学研究（英文版）)

年 卷 期：2009年第9卷第6期

页      面：641-652页

核心收录：

学科分类：0709[理学-地质学] 07[理学] 0708[理学-地球物理学] 070401[理学-天体物理] 0825[工学-航空宇航科学与技术] 0704[理学-天文学] 

基　　金：Supported by the National Natural Science Foundation of China 

主　　题：galaxies individual (M31) -- galaxies star clusters -- galaxies stellar content 

摘      要：Mayall Ⅱ = G1 is one of the most luminous globular clusters （GCs） in M31. Here, we determine its age and mass by comparing multicolor photometry with theoretical stellar population synthesis models. Based on far- and near-ultraviolet GALEX photometry, broad-band UBVRI, and infrared JHKs 2MASS data, we construct the most extensive spectral energy distribution of G 1 to date, spanning the wavelength range from 1538 to 20 000A. A quantitative comparison with a variety of simple stellar population （SSP） models yields a mean age which is consistent with G1 being among the oldest building blocks of M31 and having formed within ～1.7 Gyr after the Big Bang. Irrespective of the SSP model or stellar initial mass function adopted, the resulting mass estimates （of order 10^7M⊙） indicate that GI is one of the most massive GCs in the Local Group. However, we speculate that the cluster＇s exceptionally high mass suggests that it may not be a genuine GC. Our results also suggest that G1 may contain, on average, （1.65±0.63） × 10^2L⊙ far-ultraviolet-bright, hot, extreme horizontal-branch stars, depending on the adopted SSP model. In addition, we demonstrate that extensive multi-passband photometry coupled with SSP analysis enables one to obtain age estimates for old SSPs that have similar accuracies as those from integrated spectroscopy or resolved stellar photometry, provided that some of the free parameters can be constrained independently.