M33中的群集出生线
The cluster birthline in M33
摘要：
我们测试的可靠性红外（IR）发射跟踪恒星形成在个别恒星形成的网站M33，并概述了一种新的方法来测试大质量恒星的分布函数在新形成的集群。我们选择的IR源从斯皮策调查的M33和表明，IR和H α光度不相关。利用GALEX-UV数据补充红外测光，我们估计了源的热光度。对于一个给定的恒星IMF，我们模拟的理论曲线的预期测辐射热的H α光度比，沿星团诞生。我们称之为Lbol-Lbol/LHal平面中的星团诞生线。当Lbol> 3x 10 ^{39}erg/s时，出生线是平坦的，因为所有的星团都对IMF进行了完全采样，并且随着IMF的上端变得不完全采样，出生线向较低的亮度增加。对M33的观测表明，年轻的孤立星系团在很大范围的Lbol上都接近理论出生线。对于低质量的星团，亮度与Halpha发射不成比例，老化使星团移动到出生线以上。最适合出生线的是一个随机抽样的IMF，其中星团中质量最大的恒星的质量不受星团质量的严格限制。我们还发现M33中年轻星团的红外光度与它们的热光度不成正比。这种不规则性可能是M33中尘埃丰度较低且不均匀的结果。
英文摘要：
We test the reliability of infrared (IR) emission to trace star formation in individual star-forming sites of M33, and outline a new method for testing the distribution function of massive stars in newly formed clusters. We select IR sources from the Spitzer survey of M33 and show that the IR and Halpha luminosities are not correlated. Complementing the infrared photometry with GALEX-UV data, we estimate the source bolometric luminosities. For a given stellar IMF we simulate a theoretical curve for the expected bolometric-to-Halpha luminosity ratio, along which stellar clusters are born. We call this the cluster birthline in the Lbol--Lbol/LHal plane. The birthline is flat for Lbol>3x10^{39}erg/s because all clusters fully sample the IMF and it increases toward lower luminosities as the upper end of the IMF becomes incompletely sampled. The observations of M33 show that young isolated clusters lie close to the theoretical birthline for a wide range of Lbol. The luminosity is not proportional to Halpha emission for low mass clusters and aging moves clusters above the birthline. The best fit to the birthline is for a randomly sampled IMF, in which the mass of most massive star in a cluster is not strictly limited by the cluster's mass. We also find that the IR luminosity of young stellar clusters in M33 is not proportional to their bolometric luminosity. This irregularity could be the result of low and patchy dust abundance in M33.
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