THE H i PROBABILITY DISTRIBUTION FUNCTION and the ATOMIC-TO-MOLECULAR TRANSITION in MOLECULAR CLOUDS

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Abstract

We characterize the column-density probability distribution functions (PDFs) of the atomic hydrogen gas, H i, associated with seven Galactic molecular clouds (MCs). We use 21 cm observations from the Leiden/Argentine/Bonn Galactic H i Survey to derive column-density maps and PDFs. We find that the peaks of the H i PDFs occur at column densities in the range ∼1-2 1021 (equivalently, ∼0.5-1 mag). The PDFs are uniformly narrow, with a mean dispersion of (∼0.1 mag). We also investigate the H i-to-H2 transition toward the cloud complexes and estimate H i surface densities ranging from 7 to 16 at the transition. We propose that the H i PDF is a fitting tool for identifying the H i-to-H2 transition column in Galactic MCs.

Original languageEnglish (US)
Article number102
JournalAstrophysical Journal
Volume829
Issue number2
DOIs
StatePublished - Oct 1 2016
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • ISM: clouds
  • ISM: individual objects (Orion A, Rosette)
  • ISM: structure
  • dust, extinction
  • photondominated region (PDR)

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