Revisiting Integrated Star Formation Law. II.

This offset is seen even when a common conversion factor between CO intensity and molecular hydrogen surface density is applied, and it is confirmed when disk surface densities of interstellar dust are used as proxies for gas measurements. Tests for possible systematic biases in the starburst data fail to uncover any spurious sources for such a large offset. We tentatively conclude that the global Schmidt law in galaxies, at least as it is conventionally measured, is bimodal or possibly multimodal.

Possible causes may include changes in the small-scale structure of the molecular interstellar medium or the stellar initial mass function. A single n ~1.5 power law still remains as a credible approximation or "recipe" for analytical or numerical models of galaxy formation and evolution.