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arXiv 1503.01846astro-ph.GA
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附近富含气体星系的HI发射和吸收

HI emission and absorption in nearby, gas-rich galaxies

S. N. Reeves, E. M. Sadler, J. R. Allison, B. S. Koribalski, S. J. Curran, M. B. Pracy

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18 pages, 8 figures
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摘要：

我们提出了一个有针对性的搜索干预HI吸收附近的六个，气体丰富的星系使用澳大利亚望远镜紧凑阵列（ATCA）的结果。搜索的视线具有10-20千秒差距的碰撞参量。通过瞄准附近的星系，我们也能够映射它们的HI发射，使我们能够直接将吸收线检测率与扩展的HI分布联系起来。在六个星系中的四个中，连续谱的视线与HI盘相交，但没有检测到干涉吸收。在这四个星系中，我们发现其中三个未被探测到是背景源太暗的结果。在第四种情况下，我们发现，自旋温度的覆盖因子（$T_{\mathrm{S}}/f$）的比率必须远远高于预期（$\gtrsim$ 5700 K），以解释未检测。我们讨论了背景连续源的结构可能会影响HI吸收在我们的样品中的检测率，以及未来调查的可能影响。未来的工作，包括扩大样本，VLBI观测，将使我们能够更好地调查预期的检测率，和背景源结构的影响，对未来的调查结果。

英文摘要：

We present the results of a targeted search for intervening HI absorption in six nearby, gas-rich galaxies using the Australia Telescope Compact Array (ATCA). The sightlines searched have impact parameters of 10-20 kpc. By targeting nearby galaxies we are also able to map their HI emission, allowing us to directly relate the absorption-line detection rate to the extended HI distribution. The continuum sightlines intersect the HI disk in four of the six galaxies, but no intervening absorption was detected. Of these four galaxies, we find that three of the non-detections are the result of the background source being too faint. In the fourth case we find that the ratio of the spin temperature to the covering factor ($T_{\mathrm{S}}/f$) must be much higher than expected ($\gtrsim$5700 K) in order to explain the non-detection. We discuss how the structure of the background continuum sources may have affected the detection rate of HI absorption in our sample, and the possible implications for future surveys. Future work including an expanded sample, and VLBI observations, would allow us to better investigate the expected detection rate, and influence of background source structure, on the results of future surveys.

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