| Old stellar population synthesis： new age and mass estimates for Mayall Ⅱ = G1 |
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| 作者姓名： | 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 |
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| 作者单位： | [1]National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China [2]Department of Physics ＆ Astronomy, The University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, UK [3]Graduate University, Chinese Academy of Sciences, Beijing 100049, China [4]Department of Astronomy and Space Science, Chungnam National University, Daejeon 305-764, Korea [5]Center for Space Astrophysics, Yonsei University, Seoul 120-749, Korea [6]California Institute of Technology, MC 405-47, 1200 E. California Boulevard, Pasadena, CA 91125 |
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| 基金项目： | Supported by the National Natural Science Foundation of China.Acknowledgements We are indebted to the referee for thoughtful comments and insightful suggestions that greatly improved this paper. This work has been supported by the Chinese National Natural Science Foundation through Grant Nos. 10873016, 10803007, 10473012, 10573020, 10633020, 10673012, and 10603006; and by the National Basic Research Program of China （973 Program） No. 2007CB815403. RdG acknowledges partial financial support from the Royal Society in the form of a UK-China International Joint Project. SCR acknowledges partial support from KOSEF through the Astrophysical Research Center for the Structure and Evolution of the Cosmos （ARCSEC）. This paper makes use of data from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, funded by NASA and the National Science Foundation. This paper is also partially based on archival observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute （STScI）, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. This research has made use of NASA＇s Astrophysics Data System Abstract Service. This reasearch is partially based on archival data from the NASA GALEX mission developed in cooperation with the Centre National d＇Etudes Spatiales of France and the Korean Ministry of Science and Technology. |
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| 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.
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| 关 键 词： | 天文学 球状星团 光谱能量 宇宙大爆炸 磷酸钙 |
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