Variation of the Lifetime and Fragmentation Scale in Molecular Clouds as an Indication of Ambipolar Diffusion

Ambipolar diffusion likely plays a pivotal role in the formation and evolution of dense cores in weakly-ionized molecular clouds. Linear analyses show that the evolutionary times and fragmentation scales are significantly greater than the hydrodynamic (Jeans) values even for clouds with mildly supercritical mass-to-flux ratio. We utilize values of fragmentation scales and growth time corresponding to typical ionization fractions within a molecular cloud and apply them to the observations of the lifetime of prestellar cores and the number of embedded cores forming in a parent clump. We fit the observations of prestellar cores in the Aquila cloud identified with Herschel and obtain a range of estimated lifetimes of cores to be in the range 0.1 to a few Myr.

We also model the number of such embedded cores forming in a parent clump as found in the Perseus star-forming complex identified with the Submillimeter Array (SMA). The model makes different predictions than the standard Jeans analysis, and its concurrence with the observations provides a means to understand the formation and evolution of dense cores in molecular clouds.