| Description |
The formation of stars is a crucial process that controls the chemistry and dynamics of the interstellar medium, as well as evolution of entire galaxies. Infrared and sub-millimeter observations provide information about the star formation rate and molecular gas content, and thereby constrain the Kennicutt-Schmidt (KS) relationship. Using recent survey data, I will demonstrate variations in the KS relationship in local galaxies. Hierarchical and Bayesian statistical methods allow for a robust treatment of uncertainties, both in the assumed conversion factors and observational noise, and can reveal intrinsic variations between the individual galaxies within a sample. I show that the KS relationship varies between galaxies, and that most galaxies portray a sublinear KS trend. This is indicative of an increasing gas depletion time with increasing molecular content. These results indicate that CO observations do not solely trace star forming clouds, but also a diffuse molecular component. Other recent molecular line observations also reveal a significant diffuse gas fraction, reaching up to 30% or more of the total molecular content. The diffuse molecular gas fraction is dependent on the index of the KS relation. I also demonstrate that the scaling relationships might be related to the metallicity of the ISM.
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