The Sequential Growth of Star Formation Seeds in the Galactic Snake: Infrared Dark Cloud G11.11-0.12

We present Submillimeter Array (SMA) 1.3 and 0.88 mm broad band observations, and Very Large Array (VLA) observations in NH3 (J,K) = (1,1) up to (5,5), as well as H2O and CH3OH maser lines toward the two most massive molecular clumps in Infrared Dark Cloud (IRDC) G11.11-0.12, also known as the Snake nebula. The sensitive high-resolution images reveal hierarchical fragmentation from the ~1pc clump scale down to ~0.01pc condensation scale. At each fragmenting scale, the mass of the fragments is orders of magnitude larger than the Jeans mass. This is common to all four IRDC clumps we studied, suggesting that turbulence plays a dominant role in the initial stages of clustered star formation. Masers, shock heated NH3 gas, and outflows indicate intense ongoing star formation in some cores while none of such signatures are found in others. Furthermore, chemical differentiation between cores reflects a sequential growth of these star formation seeds. The same applies to condensations and clumps. The mass function of the resolved condensations is consistent with a power law with an index of alpha = 2.0+/-0.2 and a turnover at 2.7 solar mass. Our combined SMA+VLA observations of several IRDC clumps have presented so far the deepest view of the early stages prior to the hot core phase, revealing snapshots of physical and chemical properties at various stages along an apparent evolutionary sequence, subject to further tests by detailed modeling.