2016ApJ...833...23N

The scaling relations and star formation laws for molecular cloud complexes (MCCs) in the Milky Way are investigated. MCCs are mostly large (R > 50 pc), massive (∼106 \textM_☉) gravitationally unbound cloud structures. We compare their masses M_gas, mass surface densities Σ_Mgas_, radii R, velocity dispersions σ, star formation rates (SFRs), and SFR densities Σ_SFR with those of structures ranging from cores, clumps, and giant molecular clouds, to MCCs, and galaxies, spanning eight orders of magnitudes in size and 13 orders of magnitudes in mass. This results in the following universal relations:σ\simR^0.5,M_gas\simR²,Σ_SFR∼Σ_Mgas1.5^,SFR\simMgas_^0.9,∧\SFR∼σ^2.7. Variations in the slopes and coefficients of these relations are found at individual scales, signifying different physics acting at different scales. Additionally, there are breaks at the MCC scale in the σ–R relation and between starburst and normal star-forming objects in the SFR–M_gas and Σ_SFR-Σ_Mgas_ relations. Therefore, we propose to use the Schmidt-Kennicutt diagram to distinguish starburst from normal star-forming structures by applying a Σ_Mgas_ threshold of ∼100 \textM_☉ pc^–2 and a Σ_SFR threshold of 1 \textM_☉ yr^–1 kpc^–2. Mini-starburst complexes are gravitationally unbound MCCs that have enhanced Σ_SFR (>1 \textM_☉ yr^–1 kpc^–2), probably caused by dynamic events such as radiation pressure, colliding flows, or spiral arm gravitational instability. Because of dynamical evolution, gravitational boundedness does not play a significant role in regulating the star formation activity of MCCs, especially the mini-starburst complexes, which leads to the dynamical formation of massive stars and clusters. We emphasize the importance of understanding mini-starbursts in investigating the physics of starburst galaxies.