Speaker
Dr
Nicola Schneider
(LAB Bordeaux)
Description
Since long, there are claims that stars form only above certain thresholds of (column) density, and that the rate of star formation (SFR) in a galaxy can be linked to physical properties of the interstellar gas from which stars are forming. With the Herschel photometric maps (70-500 micron) of Galactic clouds, it is now possible to determine rather precisely their column density structure, and at the same time their pre- and protostellar content. Probability distribution functions of column density (PDFs) turned out to be one of the most important tools to estimate the relative importance of gravity, turbulence, and radiative feedback governing the cloud's density structure. From a large number of studies, based on Herschel key- and open time programs, I will show that 1. PDFs are a qualitative and quantitative measure of turbulence and gravity influencing a cloud, 2. the PDF shape depends on the gravitational collapse behaviour of filamentary clouds, 3. the determination of 'threshold' values requires a careful examination of observational biases such as line-of-sight contamination, and 4. that there is no global Kennicutt-Schmidt scaling law (power-law relation between the star-formation rate surface density and the gas surface density).
Author
Dr
Nicola Schneider
(LAB Bordeaux)