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arXiv 2103.02049astro-ph.GA
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银河系H II区人口的VLA普查

A VLA Census of the Galactic H II Region Population

William P. Armentrout, Loren D. Anderson, Trey V. Wenger, Dana S. Balser, Thomas M. Bania

备注：
11 pages of text, 146 infrared/radio images of faint HII region candidates
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摘要：

银河系包含数以千计的H II区域候选者，通过其特征的中红外形态识别，但缺乏电离气体示踪剂的检测，如无线电连续谱或无线电复合线发射。因此，这些目标仍然未被确认为H II区域。由于银河系中只有$\sim$ 2500个被证实的H II区域，与具有类似恒星形成率的外部星系相比，银河系的调查少了几千个星云。利用卡尔G. Jansky甚大阵（VLA），我们探索H II区域候选者的样本，以设置银河系H II区域的实际总人口的观测限制。我们的目标是来自银河系H II区域WISE星表中红外直径小于80 $^{\prime\prime}$的$245^{\circ}\geq\ell\geq90^{\circ}$之间的所有红外识别的“无线电安静”源。我们检测到无线电连续发射从50%的目标H II区域的候选人，提供了强有力的证据表明，大多数无线电安静的候选人是真正的H II区域。我们测量的峰值和综合无线电通量密度和比较推断莱曼连续通量使用OB-星模型。我们的结论是，大约光谱类型B2和更早的恒星能够创建H II区域与类似的红外和无线电连续形态的O-星创建的更明亮的H II区域。根据我们对“无线电静默”源的50%探测率，我们为银河系H II区的人口设定了$\sim$ 7000的下限。因此，银河系中绝大多数的H II区仍有待发现。

英文摘要：

The Milky Way contains thousands of H II region candidates identified by their characteristic mid-infrared morphology, but lacking detections of ionized gas tracers such as radio continuum or radio recombination line emission. These targets thus remain unconfirmed as H II regions. With only $\sim$2500 confirmed H II regions in the Milky Way, Galactic surveys are deficient by several thousand nebulae when compared to external galaxies with similar star formation rates. Using sensitive 9 GHz radio continuum observations with the Karl G. Jansky Very Large Array (VLA), we explore a sample of H II region candidates in order to set observational limits on the actual total population of Galactic H II regions. We target all infrared-identified "radio quiet" sources from the WISE Catalog of Galactic H II regions between $245^{\circ}\geq\ell\geq90^{\circ}$ with infrared diameters less than 80$^{\prime\prime}$. We detect radio continuum emission from 50% of the targeted H II region candidates, providing strong evidence that most of the radio quiet candidates are bona fide HII regions. We measure the peak and integrated radio flux densities and compare the inferred Lyman continuum fluxes using models of OB-stars. We conclude that stars of approximately spectral type B2 and earlier are able to create H II regions with similar infrared and radio continuum morphologies as the more luminous H II regions created by O-stars. From our 50% detection rate of "radio quiet" sources, we set a lower limit of $\sim$7000 for the H II region population of the Galaxy. Thus the vast majority of the Milky Way's H II regions remain to be discovered.

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