STAR-FORMING GAS IN YOUNG CLUSTERS

Initial conditions for star formation in clusters are estimated for protostars whose masses follow the initial mass function from 0.05 to 10 solar masses. Star-forming infall is assumed equally likely to stop at any moment, due to gas dispersal dominated by stellar feedback. For spherical infall, the typical initial condensation must have a steep density gradient, as in low-mass cores, surrounded by a shallower gradient, as in the clumps around cores. These properties match observed column densities in cluster-forming regions when the mean infall stopping time is 0.05 Myr and the accretion efficiency is 0.5. The infall duration increases with final protostar mass, from 0.01 to 0.3 Myr, and the mass accretion rate increases from 3 to 300 x 10(-6) solar masses yr(-1). The typical spherical accretion luminosity is similar to 5 solar luminosities, reducing the luminosity problem to a factor of similar to 3. The initial condensation density gradient changes from steep to shallow at radius 0.04 pc, enclosing 0.9 solar masses, with mean column density 2 x 10(22) cm(-2) and with effective central temperature 16 K. These initial conditions are denser and warmer than those for isolated star formation.