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

Ma, Jun and de Grijs, Richard and Fan, Zhou and Rey, Soo-Chang and Wu, Zhen-Yu and Zhou, Xu and Wu, Jiang-Hua and Jiang, Zhao-Ji and Chen, Jian-Sheng and Lee, Kyungsook and Sohn, Sangmo Tony (2009) Old stellar population synthesis: new age and mass estimates for Mayall II = G1. Research in Astronomy and Astrophysics, 9 (6). pp. 641-652. ISSN 1674-4527.

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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 JHK_S 2MASS data, we construct the most extensive spectral energy distribution of G1 to date, spanning the wavelength range from 1538 to 20 000 Å. 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 10^7_⊙) indicate that G1 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) × 10^2_⊙ 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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Additional Information:© Institute of Physics and IOP Publishing Limited 2009. Received 11 September 2008, accepted for publication 16 January 2009. 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 research 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.
Funding AgencyGrant Number
National Natural Science Foundation10873016
National Natural Science Foundation10803007
National Natural Science Foundation10473012
National Natural Science Foundation10573020
National Natural Science Foundation10633020
National Natural Science Foundation10673012
National Natural Science Foundation10603006
National Basic Research Program of China2007CB815403
Korea Science and Engineering FoundationUNSPECIFIED
NASANAS 5-26555
Subject Keywords:galaxies: individual (M31); galaxies: star clusters; galaxies: stellar content
Issue or Number:6
Record Number:CaltechAUTHORS:20090909-131123014
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Official Citation:Old stellar population synthesis: new age and mass estimates for Mayall II = G1 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 and Sangmo Tony Sohn 2009 Res. Astron. Astrophys. 9 641-652 doi: 10.1088/1674-4527/9/6/003.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15700
Deposited By: Tony Diaz
Deposited On:10 Sep 2009 16:50
Last Modified:03 Oct 2019 01:01

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