（U）LIRGs中光选星形成结的特性
Characterization of optically-selected star forming knots in (U)LIRGs
摘要：
本文介绍了32个低Z（U）激光激发光散射光栅（LIRGs）典型样品中光学选择致密天体（节点）的一般性质（光度函数、质量、大小、年龄等）的综合表征。我们使用哈勃太空望远镜在F435W和F814W波段的ACS图像。样本中的星系代表了不同的相互作用阶段，覆盖了很宽的光度范围（11.46 \leq log（L_IR（Lsun））\leq 12.54）。平均大小为32 pc，探测到的近3000节中的大部分由星团复合体组成。一些结（~15%）是如此蓝色，它们的颜色表明一个年轻的（即，<3000万年）和几乎无菌的人口。这些蓝结的质量与它们的半径M \propto R ^{1.91 \pm 0.14}有着明显的相关性，类似于在M51和巨分子云中发现的星团复合体。这表明，在任何给定的半径，结内的恒星形成与气体密度成正比。所有节点的恒星形成的特点是光度函数（LF）的节点与斜率接近2。然而，我们看到一个轻微的显著迹象表明，LF随着互动过程的发展而发展，从早期到高级合并阶段变得更加陡峭。由于样本大小的影响，我们可能是采样结在ULIRG本质上更明亮（x4）比在不太明亮的系统。它们的大小和质量也很可能是z \gtrsim 1的星系团的特征。在合并后的结平均更大（x 1.3 - 2），更明亮（2等）的I波段，和0.5等红比那些在早期阶段的系统。简要讨论了两种情况：（1）在最先进的合并中可能存在相对较高的灭绝;（2）质量较小的星系团的溶解和/或它们合并成质量更大的演化超星系团。
英文摘要：
(abridged)We present a comprehensive characterization of the general properties (luminosity functions, mass, size, ages, etc) of optically selected compact stellar objects (knots) in a representative sample of 32 low-z (U)LIRGs. We use ACS images from the Hubble Space Telescope in F435W and F814W bands. The galaxies in the sample represent different interaction phases and cover a wide luminosity range (11.46 \leq log (L_IR (Lsun)) \leq 12.54). With a median size of 32 pc, most of the nearly 3000 knots detected consists of complexes of star clusters. Some of the knots (~15%) are so blue that their colors indicate a young (i.e., < 30 Myr) and almost extinction-free population. There is a clear correlation of the mass of these blue knots with their radius, M \propto R^{1.91\pm0.14}, similar to that found in complexes of clusters in M51 and in Giant Molecular Clouds. This suggests that the star formation within the knots is proportional to the gas density at any given radius. The star formation of all the knots is characterized by luminosity functions (LFs) of the knots with slopes close to 2. Though, we see a marginally significant indication that the LF evolves with the interaction process, becoming steeper from early to advanced merger phases. Due to size-of-sample effects we are probably sampling knots in ULIRGs intrinsically more luminous (x4) than in less luminous systems. They also have sizes and are likely to have masses characteristic of clumps in galaxies at z \gtrsim 1. Knots in post-mergers are on average larger (x 1.3-2), more luminous (2 mag) in the I-band, and 0.5 mag redder than those in systems in earlier phases. Two scenarios are briefly discussed: (1) the likely presence of relatively high extinction in the most advanced mergers; (2) the dissolution of the less massive clusters and/or their coalescence into more massive, evolved superclusters.
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