TY - JOUR
T1 - Old stellar population synthesis
T2 - new age and mass estimates for Mayall II G1
AU - Ma, Jun
AU - de Grijs, Richard
AU - Fan, Zhou
AU - Rey, Soo-Chang
AU - Wu, Zhen-Yu
AU - Zhou, Xu
AU - Wu, Jiang-Hua
AU - Jiang, Zhao-Ji
AU - Chen, Jian-Sheng
AU - Lee, Kyungsook
AU - Sohn, Sangmo Tony
PY - 2009
Y1 - 2009
N2 - 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 U B V R I, and infrared J H K S 2MASS data, we construct the most extensive spectral energy distribution of G1 to date, spanning the wavelength range from 1538 to 20 000 . 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 107 M⊙) 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, (1.650.63) × 102 L⊙ 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.
AB - 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 U B V R I, and infrared J H K S 2MASS data, we construct the most extensive spectral energy distribution of G1 to date, spanning the wavelength range from 1538 to 20 000 . 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 107 M⊙) 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, (1.650.63) × 102 L⊙ 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.
KW - galaxies: individual (M31)
KW - galaxies: star clusters
KW - galaxies: stellar content
UR - http://www.scopus.com/inward/record.url?scp=67650671167&partnerID=8YFLogxK
U2 - 10.1088/1674-4527/9/6/003
DO - 10.1088/1674-4527/9/6/003
M3 - Article
AN - SCOPUS:67650671167
SN - 1674-4527
VL - 9
SP - 641
EP - 652
JO - Research in Astronomy and Astrophysics
JF - Research in Astronomy and Astrophysics
IS - 6
ER -