Transport-driven super-Jeans fragmentation in dynamical star-forming regions

ABSTRACT The Jeans criterion is one cornerstone in our understanding of gravitational fragmentation. A critical limitation of the Jeans criterion is that the background density is assumed to be a constant, which is often not true in dynamic conditions such as star-forming regions. For example, during the formation phase of the high-density gas filaments in a molecular cloud, a density increase rate ̇ implies a mass accumulation time of t ₀₂₂= / ̇= - ( (v) ) ^-1. The system is non-stationary when the mass accumulation time becomes comparable to the free-fall time t ₅₅ = 1 / G. We study fragmentation in non-stationary settings, and find that accretion can significantly increase in the characteristic mass of gravitational fragmentation (λJeans, aac = λJeans (1 + tff/tacc) 1/3, m ₉₄₀₍ₒ, \, ₀₂₂ = m ₉₄₀₍ₒ (1 + t ₅₅ / t ₀₂₂) ). In massive star-forming regions, this mechanism of transport-driven super-Jeans fragmentation can contribute to the formation of massive stars by causing order-of-magnitude increases in the mass of the fragments.