NGC 5253星团系统。I.标准模型和红外过量源
The NGC 5253 star cluster system. I. Standard modelling and infrared-excess sources
摘要：
利用高分辨率哈勃太空望远镜的数据，我们重新研究了矮星暴星系NGC 5253中丰富星团人口的基本属性（年龄，质量和消光值）。与以前的研究相比，分辨率的增益在两个空间维度上都是两个因素的顺序，而我们的可访问波长范围超越了以前的研究，通过将近紫外和近红外（IR）通带。我们应用光谱合成处理的基础上，两个不同的简单的恒星星族模型套件，我们的一组中，宽带和H-α图像，以获得更好的物理理解的IR过剩通量的一个子集的年轻的集群（30 149）。需要说明的是，我们的模型是基于完全采样的恒星质量函数，NGC 5253星系团中主要是大量相对低质量（M_cl <=几个10^4 Msun）的天体，年龄从几× 10^6到几× 10^7年不等，这与宿主星系的星暴年龄非常吻合。红外线过剩的星系团几乎都是在这个年轻的年龄范围内发现的，质量可达几× 10^4 M太阳。相对低质量的NGC 5253星团中的红外过量很可能是由随机采样效应和由于存在明亮的红色或前主序星而导致的颜色变化引起的。我们还发现了少量的中等年龄（~ 1 Gyr）、~10^5 Msun的星团，以及多达12个大质量、~10 Gyr的球状星团。它们的存在支持了NGC 5253是一个非常活跃的星系，经历了多个团簇形成的观点。
英文摘要：
Using high-resolution Hubble Space Telescope data, we reexamine the fundamental properties (ages, masses and extinction values) of the rich star cluster population in the dwarf starburst galaxy NGC 5253. The gain in resolution compared to previous studies is of order a factor of two in both spatial dimensions, while our accessible wavelength range transcends previous studies by incorporation of both near-ultraviolet and near-infrared (IR) passbands. We apply spectral synthesis treatments based on two different simple stellar population model suites to our set of medium-, broad-band and H-alpha images to gain an improved physical understanding of the IR-excess flux found for a subset of young clusters (30 of 149). With the caveat that our models are based on fully sampled stellar mass functions, the NGC 5253 cluster population is dominated by a significant number of relatively low-mass (M_cl <= a few 10^4 Msun) objects with ages ranging from a few x 10^6 to a few x 10^7 yr, which is in excellent agreement with the starburst age of the host galaxy. The IR-excess clusters are almost all found in this young age range and have masses of up to a few x 10^4 Msun. The IR excess in the relatively low-mass NGC 5253 clusters is most likely caused by a combination of stochastic sampling effects and colour variations due to the presence of either luminous red or pre-main-sequence stars. We also find a small number of intermediate-age (~ 1 Gyr-old), ~10^5 Msun clusters, as well as up to a dozen massive, ~10 Gyr-old globular clusters. Their presence supports the notion that NGC 5253 is a very active galaxy that has undergone multiple episodes of star cluster formation.
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