Stellar Populations across the NGC 4244 Truncated Galactic Disk
Stellar Populations across the NGC 4244 Truncated Galactic Disk
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NGC 4244 截断银盘上的恒星族群
DOI：
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发表时间：
2007
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影响因子：
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通讯作者：
D. Zucker
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作者：
R. D. de Jong;A. Seth;D. Radburn;E. Bell;T. Brown;J. Bullock;S. Courteau;J. Dalcanton;H. Ferguson;P. Goudfrooij;S. Holfeltz;B. Holwerda;C. Purcell;J. Sick;D. Zucker
我们使用哈勃太空望远镜ACS研究附近的，几乎边缘的星系NGC 4244在其外盘表面密度突破解决恒星种群。恒星测光使我们能够研究不同恒星群体的分布，并达到很低的等效表面亮度。我们发现，断裂发生在相同的半径为年轻，中年和老年恒星。突破点以外的恒星密度急剧下降，每5千秒差距至少下降600倍。破裂发生在相同的半径上，与盘上方的高度无关，但在中平面最尖锐，在大高度处几乎消失。这些结果表明，截断不太可能是由星星形成阈值单独引起的：尽管存在着潜在的扰动，如由内部过程引起的气体的坍缩和重新分布，但从小于1亿年到10亿年前，该阈值必须保持相同的径向位置。截断形成的动力学解释更有可能，例如由于杆或密度波的角动量重新分配，或暗物质subhalos的轰击引起的恒星加热和剥离。后一种解释也与我们在星系周围看到的小弥散分量在数量上一致。
We use the Hubble Space Telescope ACS to study the resolved stellar populations of the nearby, nearly edge-on galaxy NGC 4244 across its outer disk surface density break. The stellar photometry allows us to study the distribution of different stellar populations and reach very low equivalent surface brightnesses. We find that the break occurs at the same radius for young, intermediate-age, and old stars. The stellar density beyond the break drops sharply by a factor of at least 600 in 5 kpc. The break occurs at the same radius independent of height above the disk, but is sharpest in the midplane and nearly disappears at large heights. These results make it unlikely that truncations are caused by a star formation threshold alone: the threshold would have to keep the same radial position from less than 100 Myr to 10 Gyr ago, in spite of potential disturbances such as infall and redistribution of gas by internal processes. A dynamical interpretation of truncation formation is more likely, such as due to angular momentum redistribution by bars or density waves, or heating and stripping of stars caused by the bombardment of dark matter subhalos. The latter explanation is also in quantitative agreement with the small diffuse component we see around the galaxy.