POX 186: A Dwarf Galaxy in the Process of Formation?
POX 186: A Dwarf Galaxy in the Process of Formation?
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POX 186：正在形成过程中的矮星系？
DOI：
10.1086/344297
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
W. Vacca
中科院分区：
文献类型：
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作者：
M. Corbin;W. Vacca
我们展示了用哈勃太空望远镜的行星相机2获得的“超致密”蓝矮星POX 186的U波段、V波段和I波段的深层图像。我们还利用空间望远镜成像光谱仪获得了该物体的近紫外线光谱，并将其与新的地面光谱相结合。图像证实该星系非常小，最大范围仅为300pC，光度约为10-4L*，估计质量约为107M☉。它的形态是高度不对称的，西侧有一条可能是潮汐起源的物质尾巴。U波段图像显示，这条尾巴是恒星最近形成的物质流的一部分。然而，星系中的大多数恒星形成都集中在一个中心致密(d~10-15 pc)的星团中。我们估计这个星系团的总质量约为105M☉，正在以低于0.05Yr-1的速度形成恒星，最大年龄为数百万年。银河系的外部区域明显比星系团更红，V-I颜色与K和M恒星占主导地位的星系群一致。通过对光谱的分析，我们发现该星系的金属丰度Z≃为0.06Z☉，并含有大量的内部尘埃[E(B-V)≃0.28]；这两个值都与先前的估计一致。虽然这些结果排除了早先关于POX 186是一个原星系的猜测，但它的形态、质量和活跃的恒星形成表明，它代表着最近(约108年内)两个星系下大小(约100 pC)的恒星之间的碰撞。因此，POX 186可能是一个非常小的矮星系，从动力学上讲，它仍处于形成过程中。这一解释得到了这样一个事实的支持，即它位于一个空洞中，因此它的形态不能解释为与更大质量的星系相遇的结果。这么小的恒星团块可能代表了星系形成的分层模型所需的积木，这些结果也支持了最近的星系形成图，即质量最小的天体是最后形成的。
We present deep U-, V-, and I-band images of the "ultracompact" blue dwarf galaxy POX 186 obtained with the Planetary Camera 2 of the Hubble Space Telescope. We have also obtained a near-ultraviolet spectrum of the object with the Space Telescope Imaging Spectrograph and combine this with a new ground-based optical spectrum. The images confirm the galaxy to be extremely small, with a maximum extent of only 300 pc, a luminosity of ~10-4L*, and an estimated mass of ~107 M☉. Its morphology is highly asymmetric, with a tail of material on its western side that may be tidal in origin. The U-band image shows this tail to be part of a stream of material in which stars have recently formed. Most of the star formation in the galaxy is, however, concentrated in a central, compact (d ~ 10-15 pc) star cluster. We estimate this cluster to have a total mass of ~105 M☉, to be forming stars at a rate of less than 0.05 yr-1, and to have a maximum age of a few million years. The outer regions of the galaxy are significantly redder than the cluster, with V-I colors consistent with a population dominated by K and M stars. From our analysis of the optical spectrum we find the galaxy to have a metallicity Z ≃ 0.06 Z☉ and to contain a significant amount of internal dust [E(B-V) ≃ 0.28]; both values agree with previous estimates. While these results rule out earlier speculation that POX 186 is a protogalaxy, its morphology, mass, and active star formation suggest that it represents a recent (within ~108 yr) collision between two clumps of stars of subgalactic size (~100 pc). POX 186 may thus be a very small dwarf galaxy that, dynamically speaking, is still in the process of formation. This interpretation is supported by the fact that it resides in a void, so its morphology cannot be explained as the result of an encounter with a more massive galaxy. Clumps of stars this small may represent the building blocks required by hierarchical models of galaxy formation, and these results also support the recent "downsizing" picture of galaxy formation in which the least massive objects are the last to form.
DOI：
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发表时间：
1985
期刊：
--
影响因子：
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作者：
Related Objects;J. Tran;D. Kunth;T. Thuan
通讯作者：
Related Objects;J. Tran;D. Kunth;T. Thuan