4.7 Article

Exploring the Properties of Warm and Cold Atomic Hydrogen in the Taurus and Gemini Regions

期刊

ASTROPHYSICAL JOURNAL
卷 880, 期 2, 页码 -

出版社

IOP PUBLISHING LTD
DOI: 10.3847/1538-4357/ab2b9f

关键词

ISM: clouds; ISM: structure; radio lines: ISM

资金

  1. Australian Research Council (ARC) DECRA Fellowship [DE170101086]
  2. Collaborative Research Council 956 - Deutsche Forschungsgemeinschaft (DFG)
  3. National Science Foundation Astronomy and Astrophysics Postdoctoral Fellowship [AST-1801471]
  4. NSF
  5. University of California
  6. University of Wisconsin
  7. Australian Research Council [DE170101086] Funding Source: Australian Research Council

向作者/读者索取更多资源

We report Arecibo 21 cm absorption-emission observations to characterize the physical properties of neutral hydrogen (H I) in the proximity of five giant molecular clouds (GMCs): Taurus, California, Rosette, Mon OB1, and NGC 2264. Strong H I absorption was detected toward all 79 background-continuum sources in the similar to 60 x 20 square degree region. Gaussian decompositions were performed to estimate temperatures, optical depths, and column densities of the cold and warm neutral medium (CNM and WNM). The properties of individual CNM components are similar to those previously observed along random Galactic sightlines and in the vicinity of molecular clouds, suggesting a universality of cold H I properties. The CNM spin temperature (T-s) histogram peaks at similar to 50 K. The turbulent Mach numbers of CNM components vary widely, with a typical value of similar to 4, indicating that their motions are supersonic. About 60% of the total H I gas is WNM, and nearly 40% of the WNM lies in thermally unstable regime 500-5000 K. The observed CNM fraction is higher around GMCs than in diffuse regions, and increases with increasing column density (N-H (I)) to a maximum of similar to 75%. On average, the optically thin approximation (N-H I*) underestimates the total column density by similar to 21%, but we find large regional differences in the relationship between N-H I and the required correction factor, f = N-H (I)/N-H I*. We examine two different methods (linear fit off versus log(10)(N-H I*) and uniform T-s) to correct for opacity effects using emission data from the GALFA-H I survey. We prefer the uniform T-s method because the linear relationship does not produce convincing fits for all subregions.

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