再访双极Galerkin（NGC 4038/4039）：ACS和NICMOS对一次典型合并的观察
The Antennae Galaxies (NGC 4038/4039) Revisited: ACS and NICMOS Observations of a Prototypical Merger
摘要：
ACS和NICMOS已经被用来获得NGC 4038/4039（“彗星”）的新HST图像。这些新的观测使我们能够更好地区分紧凑的星团和单个恒星，根据大小和颜色。我们利用这种能力将星系团光度函数在我们以前的WFPC 2结果基础上扩展了大约两个星等，发现它仍然是一个单一的幂律，dN/dL propto L^alpha，其中alpha=-2.13+/-0.07，直到观测极限Mv~-7。类似地，对于年龄t<3x10^8年的星系团，质量函数是一个单一的幂律dN/dM propto M^beta，其中beta=-2.10+/-0.20，对应于10^4到10^5 Msun的质量下限，取决于子样本的年龄范围。因此，光度函数和质量函数的幂律指数本质上是相同的。中等年龄星团的光度函数（即，在环、尾和外部区域发现的约1亿~ 3亿年的天体）在Mv~-6以下没有弯曲或翻转，这与弛豫驱动的星系团破裂模型相一致，该模型预测在Mv~-4之前不应该观察到翻转。对不同环境中单个~0.5 kpc大小区域的分析表明，α和β值之间存在良好的一致性，与系统中集群总人口的结果相似。研究的几个地区显示出年龄梯度的证据，有些老的集群似乎引发了年轻集群的形成。结B周围的区域是一个特别有趣的例子，一个大约1000万~ 5000万年前的星团，估计质量约为10^6 Msun，显然引发了沿着尘埃带的几个更年轻、更大质量（高达5x10^6 Msun）的星团的形成。
英文摘要：
The ACS and NICMOS have been used to obtain new HST images of NGC 4038/4039 ("The Antennae"). These new observations allow us to better differentiate compact star clusters from individual stars, based on both size and color. We use this ability to extend the cluster luminosity function by approximately two magnitudes over our previous WFPC2 results, and find that it continues as a single power law, dN/dL propto L^alpha with alpha=-2.13+/-0.07, down to the observational limit of Mv~-7. Similarly, the mass function is a single power law dN/dM propto M^beta with beta=-2.10+/-0.20 for clusters with ages t<3x10^8 yr, corresponding to lower mass limits that range from 10^4 to 10^5 Msun, depending on the age range of the subsample. Hence the power law indices for the luminosity and mass functions are essentially the same. The luminosity function for intermediate-age clusters (i.e., ~100-300 Myr old objects found in the loops, tails, and outer areas) shows no bend or turnover down to Mv~-6, consistent with relaxation-driven cluster disruption models which predict the turnover should not be observed until Mv~-4. An analysis of individual ~0.5-kpc sized areas over diverse environments shows good agreement between values of alpha and beta, similar to the results for the total population of clusters in the system. Several of the areas studied show evidence for age gradients, with somewhat older clusters appearing to have triggered the formation of younger clusters. The area around Knot B is a particularly interesting example, with an ~10-50 Myr old cluster of estimated mass ~10^6 Msun having apparently triggered the formation of several younger, more massive (up to 5x10^6 Msun) clusters along a dust lane.
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