From Globular Clusters to Tidal Dwarfs: Structure Formation in the Tidal Tails of Merging Galaxies
From Globular Clusters to Tidal Dwarfs: Structure Formation in the Tidal Tails of Merging Galaxies
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从球状星团到潮汐矮星：合并星系潮汐尾部的结构形成
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发表时间：
2003
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通讯作者：
D. Zaritsky
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作者：
K. Knierman;K. Knierman;S. Gallagher;S. Gallagher;J. Charlton;S. Hunsberger;B. Whitmore;A. Kundu;J. Hibbard;D. Zaritsky
利用哈勃太空望远镜的宽视场行星照相机2（WFPC 2）获得的V和I图像，我们研究了潮汐尾内的致密恒星结构。为了探索星星的形成如何依赖于局部和全球的物理条件，研究了四个经典的“图姆雷序列”合并中的六个潮汐碎片区域：NGC 4038/39（“潮汐”）、NGC 3256、NGC 3921和NGC 7252（“和平的原子”）。这些合并样本的演化序列和尾巴的一系列阶段，并没有嵌入潮汐矮星系。这六条尾巴被发现包含各种各样的恒星结构，大小从球状星团到矮星系不等。从V和I WFPC 2图像中，我们测量了星星团的亮度和颜色。NGC 3256被发现有大量的蓝色星团（0.2 V-I 0.9），特别是在它的西尾，类似于合并的内部区域。相比之下，NGC 4038/39在观测到的尾部区域没有星团，只有不太明亮的点源，可能是个别恒星。NGC 3921和NGC 7252在它们的尾部沿着有少量的星团。一个重要的星团人口显然与NGC 7252东部和西部尾部的突出潮汐矮候选者有关。NGC 3256的西尾并没有根据它的动力学年龄或它的总H I质量来区分。然而，在尾部几乎没有星团的合并星系都有潮汐矮星系，而NGC 3256没有突出的潮汐矮星系。我们推测，潮汐尾中的星星形成可能表现为像沿着尾巴的星系团这样的小结构，也可能表现为像矮星系这样的大结构，但不是两者都有。此外，NGC 3256在所研究的四次合并中具有最高的星星形成率，这可能有助于其潮汐尾中大量的星星团。
Using V and I images obtained with the Wide Field Planetary Camera 2 (WFPC2) of the Hubble Space Telescope, we investigate compact stellar structures within tidal tails. Six regions of tidal debris in the four classic "Toomre sequence" mergers: NGC 4038/39 ("Antennae"), NGC 3256, NGC 3921, and NGC 7252 ("Atoms for Peace") have been studied in order to explore how the star formation depends on the local and global physical conditions. These mergers sample a range of stages in the evolutionary sequence and tails with and without embedded tidal dwarf galaxies. The six tails are found to contain a variety of stellar structures, with sizes ranging from those of globular clusters up to those of dwarf galaxies. From V and I WFPC2 images, we measure the luminosities and colors of the star clusters. NGC 3256 is found to have a large population of blue clusters (0.2 ≲ V-I ≲ 0.9), particularly in its western tail, similar to those found in the inner region of the merger. In contrast, NGC 4038/39 has no clusters in the observed region of the tail, only less luminous point sources likely to be individual stars. NGC 3921 and NGC 7252 have small populations of clusters along their tails. A significant cluster population is clearly associated with the prominent tidal dwarf candidates in the eastern and western tails of NGC 7252. The cluster-rich western tail of NGC 3256 is not distinguished from the others by its dynamical age or by its total H I mass. However, the mergers that have few clusters in the tail all have tidal dwarf galaxies, while NGC 3256 does not have prominent tidal dwarfs. We speculate that star formation in tidal tails may manifest itself either in small structures like clusters along the tail or in large structures such as dwarf galaxies, but not in both. Also, NGC 3256 has the highest star formation rate of the four mergers studied, which may contribute to the high number of star clusters in its tidal tails.