Journal
ASTROPHYSICAL JOURNAL LETTERS
Volume 811, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/2041-8205/811/2/L28
Keywords
dust, extinction; galaxies: star formation; magnetohydrodynamics (MHD)
Categories
Funding
- NASA Einstein Postdoctoral Fellowship
- SYMPATICO grant from the French Agence Nationale de la Reserche [ANR-11-BS56-0023]
- DIM ACAV
- NSF Graduate Research Fellowship
- NSF Early Career Development (CAREER) Award [AST-1056780]
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The shape of the probability distribution function (PDF) of molecular clouds is an important ingredient for modern theories of star formation and turbulence. Recently, several studies have pointed out observational difficulties with constraining the low column density (i.e., A(V) < 1) PDF using dust tracers. In order to constrain the shape and properties of the low column density PDF, we investigate the PDF of multiphase atomic gas in the Perseus molecular cloud using opacity-corrected GALFA-HI data and compare the PDF shape and properties to the total gas PDF and the N(H-2) PDF. We find that the shape of the PDF in the atomic medium of Perseus is well described by a lognormal distribution and not by a power-law or bimodal distribution. The peak of the atomic gas PDF in and around Perseus lies at the HI-H-2 transition column density for this cloud, past which the N(H-2) PDF takes on a power-law form. We find that the PDF of the atomic gas is narrow, and at column densities larger than the HI-H-2 transition, the HI rapidly depletes, suggesting that the HI PDF may be used to find the HI-H-2 transition column density. We also calculate the sonic Mach number of the atomic gas by using HI absorption line data, which yield a median value of M-s = 4.0 for the CNM, while the HI emission PDF, which traces both the WNM and CNM, has a width more consistent with transonic turbulence.
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