EPoS Contribution
EPoS Contribution
Probability distribution function (PDF) of the atomic and molecular hydrogen of the giant filament GMF38.1-32.4

Simon Bihr
MPIA, Heidelberg, DE
Probability distribution functions (PDFs) of the column density of hydrogen are a common tool to examine molecular clouds. Due to turbulent motions, the initial PDFs are expected to have a log-normal shape and evolve into a power-law tail due to collapse and gravitational forces. To date, such studies are mostly limited to the molecular content of the cloud. In my talk, I will present a study of the giant filament GMF38.1-32.4, in which we calculate column density PDFs of the atomic as well as the molecular content and study the corresponding kinematics. We extracted a long HI self absorption (HISA) feature, which correlates partly with CO emission. The column density of the cold absorbing HI is on the order of 1020-1021 cm-2. In contrast to this, the column density of the molecular hydrogen, traced with CO, is an order of magnitude higher. The shape of the atomic PDF can be fit by a log normal shape, indicating turbulent motion as the main driver. This interpretation is supported by the measured linewidth of delta v(FWHM) = 6-8 km/s. This and further observations in the framework of the THOR survey (The HI, OH, Recombination Line Survey of the Milky Way) of cold absorbing HI will be an important characterization of the transition between the atomic and molecular phase and influence simulations as well as theoretical studies.
Caption: The column density PDFs of the atomic as well as the molecular hydrogen. The atomic hydrogen is determine via extracting an HI self absorption (HISA) feature and assuming a spin temperature. The molecular hydrogen is traced via 13CO observations from the GRS survey, assuming optically thin emission and assuming an appropriate excitation temperature. The grey curves indicate a log-normal shape.
H. Beuther, MPIA, DE
K.G. Johnston, U Leeds, GB
M. Rugel, MPIA, DE
J. Ott, NRAO, US
L.D. Anderson, WVirginia U, US
and the THOR team
Suggested Session: Molecular Clouds