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arXiv 1402.3029astro-ph.GAastro-ph.CO
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M33中的星团：更新的UBVRI光度学、年龄、金属丰度和质量

Star clusters in M33: updated UBVRI photometry, ages, metallicities, and masses

Zhou Fan, Richard de Grijs

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32 pages, 12 figures, 2 tables, accepted for publication in ApJS
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摘要：

M33星团的光度特征还远未完成。在本文中，我们提出了均匀的$UBVRI$测光的708个星团和集群候选人在M33的基础上档案图像从本地组银河系巡天，其中涵盖0.8度$^2$沿星系的主轴。我们的测光包括387，563，616，580，和478个对象在$UBVRI$波段，分别，其中276，405，430，457，和363没有以前公布的$UBVRI$测光。我们的测光与所有滤光片的先前测量结果（如有）一致。我们采用斯隆数字巡天$ugriz$测光作为补充，并在可用的情况下采用2微米全天巡天近红外$JHK$测光。我们拟合了671个星团和候选星团的光谱能量分布，根据更新的{ \sc秒差距}简单恒星种群合成模型推导出它们的年龄、金属丰度和质量。我们的$χ^2$最小化程序的结果表明，只有205的671个星团（$31\%$）的年龄超过2 Gyr，这代表了一个小得多的集群人口比在M31（$56\%$），这表明M33是由年轻的星团（$<1$ Gyr）。我们研究了M33、M31、银河系和大麦哲伦星云中疏散星团和球状星团的质量分布。其平均值分别为$\log(M_{\rm cl}/M_{\odot})=4.25$、5.43、2.72和4.18。开放到球状星团的比例在银河系中最高，在M31中最低。我们的集群年龄，质量和金属丰度的比较表明，我们的结果基本上是一致的，与以前的研究（在共同的对象是可用的）;差异可以追溯到所采用的模型，所使用的拟合方法和随机抽样效果的差异。

英文摘要：

The photometric characterization of M33 star clusters is far from complete. In this paper, we present homogeneous $UBVRI$ photometry of 708 star clusters and cluster candidates in M33 based on archival images from the Local Group Galaxies Survey, which covers 0.8 deg$^2$ along the galaxy's major axis. Our photometry includes 387, 563, 616, 580, and 478 objects in the $UBVRI$ bands, respectively, of which 276, 405, 430, 457, and 363 do not have previously published $UBVRI$ photometry. Our photometry is consistent with previous measurements (where available) in all filters. We adopted Sloan Digital Sky Survey $ugriz$ photometry for complementary purposes, as well as Two Micron All-Sky Survey near-infrared $JHK$ photometry where available. We fitted the spectral-energy distributions of 671 star clusters and candidates to derive their ages, metallicities, and masses based on the updated {\sc parsec} simple stellar populations synthesis models. The results of our $χ^2$ minimization routines show that only 205 of the 671 clusters ($31\%$) are older than 2 Gyr, which represents a much smaller fraction of the cluster population than that in M31 ($56\%$), suggesting that M33 is dominated by young star clusters ($<1$ Gyr). We investigate the mass distributions of the star clusters---both open and globular clusters---in M33, M31, the Milky Way, and the Large Magellanic Cloud. Their mean values are $\log(M_{\rm cl}/M_{\odot})=4.25$, 5.43, 2.72, and 4.18, respectively. The fraction of open to globular clusters is highest in the Milky Way and lowest in M31. Our comparisons of the cluster ages, masses, and metallicities show that our results are basically in agreement with previous studies (where objects in common are available); differences can be traced back to differences in the models adopted, the fitting methods used, and stochastic sampling effects.

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