静态孤立：光学致密矮星系ADBS 113845 + 2008的极度扩展的HI晕
Quiescent Isolation: The Extremely Extended HI Halo of the Optically Compact Dwarf Galaxy ADBS 113845+2008
摘要：
我们提出了新的光学成像和光谱学和HI谱线的矮星系ADBS 113845 + 2008（以下简称ADBS 1138）的成像。这个贫金属（Z~30%Z_Sun）的“后星暴”系统是迄今为止已知的任何星系中最紧凑的恒星分布之一（B波段指数尺度长度= 0.57 kpc）。与致密的恒星成分形成鲜明对比的是，中性气体的范围非常广;在10^19 cm ^-2能级（> 44个B带标度长度）上，HI的径向距离约为25 kpc。与文献中类似的“巨盘”矮星系的测量结果相比，ADBS 1138具有已知最大的HI-光学尺寸比。恒星部分位于HI的一个破碎环的中心附近，该环直径约为15 kpc;在这个结构中，柱密度的峰值在约3.5 x 10^20 cm ^-2水平。在这个环的中心，在一个相对较低的HI柱密度的区域，我们发现正在进行的恒星形成跟踪H α发射。我们将旋转曲线采样到翻转点;这限制了星系的暗物质晕的大小，它比发光成分（恒星+气体）至少重15倍。为了解释这些神秘的属性，我们研究“由内而外”和“由外而内”的进化场景。恒星形成的能量计算表明，“反馈”从集中的恒星形成是不能够产生的环结构，我们认为，这是一个系统中的大HI磁盘是在静态隔离发展。从全球范围来看，这个系统在将中性气体转化为恒星方面效率极低。
英文摘要：
We present new optical imaging and spectroscopy and HI spectral line imaging of the dwarf galaxy ADBS 113845+2008 (hereafter ADBS 1138). This metal-poor (Z~30% Z_Sun), "post-starburst" system has one of the most compact stellar distributions known in any galaxy to date (B-band exponential scale length =0.57 kpc). In stark contrast to the compact stellar component, the neutral gas is extremely extended; HI is detected to a radial distance of ~25 kpc at the 10^19 cm^-2 level (>44 B-band scale lengths). Comparing to measurements of similar "giant disk" dwarf galaxies in the literature, ADBS 1138 has the largest known HI-to-optical size ratio. The stellar component is located near the center of a broken ring of HI that is ~15 kpc in diameter; column densities peak in this structure at the ~3.5x10^20 cm^-2 level. At the center of this ring, in a region of comparatively low HI column density, we find ongoing star formation traced by H alpha emission. We sample the rotation curve to the point of turn over; this constrains the size of the dark matter halo of the galaxy, which outweighs the luminous component (stars + gas) by at least a factor of 15. To explain these enigmatic properties, we examine "inside-out" and "outside-in" evolutionary scenarios. Calculations of star formation energetics indicate that "feedback" from concentrated star formation is not capable of producing the ring structure; we posit that this is a system where the large HI disk is evolving in quiescent isolation. In a global sense, this system is exceedingly inefficient at converting neutral gas into stars.
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