On Schmidt's Conjecture and Star Formation Scaling Laws

TL;DR

This paper reviews the historical and recent empirical relations between interstellar gas properties and star formation rates, highlighting the shift from Schmidt's conjecture to a linear relation with dense gas, and discusses implications for galaxy-scale laws.

Contribution

It clarifies the transition from the original Schmidt conjecture to the current understanding of star formation scaling laws across different scales.

Findings

Linear relation between SFR and dense gas in molecular clouds.

No Schmidt relation observed between individual GMCs.

Implications for interpreting the Kennicutt-Schmidt law.

Abstract

Ever since the pioneering work of Schmidt a half-century ago there has been great interest in finding an appropriate empirical relation that would directly link some property of interstellar gas with the process of star formation within it. Schmidt conjectured that this might take the form of a power-law relation between the rate of star formation (SFR) and the surface density of interstellar gas. However, recent observations suggest that a linear scaling relation between the total SFR and the amount of dense gas within molecular clouds appears to be the underlying physical relation that most directly connects star formation with interstellar gas from scales of individual GMCs to those encompassing entire galaxies both near and far. Although Schmidt relations are found to exist within local GMCs, there is no Schmidt relation observed between GMCs. The implications of these results for interpreting and understanding the Kennicutt-Schmidt scaling law for galaxies are discussed.