EPoS Contribution
EPoS Contribution
Star formation rates from Galactic molecular clouds to galaxies

Jan Forbrich
Vienna Univ./SAO, Vienna/Cambridge, Austria/USA
The current picture of star formation has mostly been assembled from detailed observations of nearby star-forming regions. It is, however, unclear to what degree conclusions from such observations are universal and representative for the entire Galaxy. In this presentation, we discuss an extension of the current picture of star formation, as derived from observations in the Galactic neighborhood, to galaxy-wide scales when compared to observations of external galaxies. In particular, we investigate scaling relations between star formation rates and measurements of both dense and total molecular gas masses. We argue that there is a fundamental empirical scaling relation that directly connects the local star formation process with that operating globally within galaxies. Specifically, the total star formation rate in a molecular cloud or galaxy is linearly proportional to the mass of dense gas within the cloud or galaxy. This simple relation, first documented in previous studies, holds over a span of mass covering nearly nine orders of magnitude and indicates that the rate of star formation is directly controlled by the amount of dense molecular gas that can be assembled within a star formation complex. We further show that the star formation rates and total molecular masses, characterizing both local clouds and galaxies, are correlated over similarly large scales of mass and can be described by a linear star formation scaling law, parameterized by the fraction of dense gas contained within the clouds or galaxies. That is, the underlying star formation scaling law is always linear for clouds and galaxies with the same dense gas fraction. These considerations provide a single unified framework for understanding the relation between the standard (nonlinear) extragalactic Schmidt-Kennicutt scaling law, that is typically derived from CO observations of the gas, and the linear star formation scaling law derived from HCN observations of the dense gas.
Charlie Lada, CfA, USA
Joao Alves, Vienna Univ., Austria
Marco Lombardi, Univ. of Milan, Italy
Key publication