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

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 rho(center dot) implies a mass accumulation time of t(acc)= rho/rho(center dot)= -rho(del & sdot;(rho v(->)))(-1). The system is non-stationary when the mass accumulation time becomes comparable to the free-fall time t(ff)=1/G rho. We study fragmentation in non-stationary settings, and find that accretion can significantly increase in the characteristic mass of gravitational fragmentation (lambda(Jeans, aac) = lambda(Jeans)(1 + t(ff)/t(acc))(1/3), m(Jeans,acc)= m(Jeans)(1+t(ff)/t(acc))). 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.