The "Nessie" Nebula is a filamentary infrared dark cloud (IRDC) with a large aspect ratio of over 150:1 (1.5 • × 0.01 • , or 80 pc × 0.5 pc at a kinematic distance of 3.1 kpc). Maps of HNC (1-0) emission, a tracer of dense molecular gas, made with the Australia Telescope National Facility Mopra telescope, show an excellent morphological match to the mid-IR extinction. Moreover, because the molecular line emission from the entire nebula has the same radial velocity to within ±3.4 km s −1 , the nebula is a single, coherent cloud and not the chance alignment of multiple unrelated clouds along the line of sight.The Nessie Nebula contains a number of compact, dense molecular cores which have a characteristic projected spacing of ∼ 4.5 pc along the filament. The theory of gravitationally bound gaseous cylinders predicts the existence of such cores, which, due to the "sausage" or "varicose" fluid instability, fragment from the cylinder at a characteristic length scale. If turbulent pressure dominates over thermal pressure in Nessie, then the observed core spacing matches theoretical -2predictions. We speculate that the formation of high-mass stars and massive star clusters arises from the fragmentation of filamentary IRDCs caused by the "sausage" fluid instability that leads to the formation of massive, dense molecular cores. The filamentary molecular gas clouds often found near high-mass starforming regions (e.g., Orion, NGC 6334, etc.) may represent a later stage of IRDC evolution.

We have observed 37 Infrared Dark Clouds (IRDCs), containing a total of 159 clumps, in highdensity molecular tracers at 3 mm using the 22-meter ATNF Mopra Telescope located in Australia. After determining kinematic distances, we eliminated clumps that are not located in IRDCs and clumps with a separation between them of less than one Mopra beam. Our final sample consists of 92 IRDC clumps. The most commonly detected molecular lines are (detection rates higher than 8%): N 2 H + , HNC, HN 13 C, HCO + , H 13 CO + , HCN, C 2 H, HC 3 N, HNCO, and SiO. We investigate the behavior of the different molecular tracers and look for chemical variations as a function of an evolutionary sequence based on Spitzer IRAC and MIPS emission. We find that the molecular tracers behave differently through the evolutionary sequence and some of them can be used to yield useful relative age information. The presence of HNC and N 2 H + lines do not depend on the star formation activity. On the other hand, HC 3 N, HNCO, and SiO are predominantly detected in later stages of evolution. Optical depth calculations show that in IRDC clumps the N 2 H + line is optically thin, the C 2 H line is moderately optically thick, and HNC and HCO + are optically thick. The HCN hyperfine transitions are blended, and, in addition, show self-absorbed line profiles and extended wing emission. These factors combined prevent the use of HCN hyperfine transitions for the calculation of physical parameters. Total column densities of the different molecules, except C 2 H, increase with the evolutionary stage of the clumps. Molecular abundances increase with the evolutionary stage for N 2 H + and HCO + . The N 2 H + /HCO + and N 2 H + /HNC abudance ratios act as chemical clocks, increasing with the evolution of the clumps.

ALMA will revolutionize our understanding of star formation within our galaxy, but before we can use ALMA we need to know where to look. The Millimeter Astronomy Legacy Team 90 GHz (MALT90) Survey is a large international project to map the molecular line emission of over 2,000 dense clumps in the Galactic plane. MALT90 serves as a pathfinder mission for ALMA, providing a large public database of dense molecular clumps associated with high-mass star formation. In this proceedings, we describe the survey parameters and share early science highlights from the survey, including (1) a comparison between galactic and extragalactic star formation relations, (2) chemical trends in MALT90 clumps, (3) the distribution of high-mass star formation in the Milky Way, and (4) a discussion of the "Brick", the target of successful ALMA Cycle 0 and Cycle 1 proposals.

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We have used deep near-infrared observations with adaptive optics to discover a distributed population of low-mass protostars within the filamentary Infrared Dark Cloud G34.43+00.24. We use maps of dust emission at multiple wavelengths to determine the column density structure of the cloud. In combination with an empirically verified model of the magnitude distribution of background stars, this column density map allows us to reliably determine overdensities of red sources that are due to embedded protostars in the cloud. We also identify protostars through their extended emission in the K band which comes from excited H 2 in protostellar outflows or reflection nebulosity. We find a population of distributed low-mass protostars, suggesting that low-mass protostars may form earlier than, or contemporaneously with, high-mass protostars in such a filament. The low-mass protostellar population may also produce the narrow line-width SiO emission observed in some clouds without high-mass protostars. Finally, we use a molecular line map of the cloud to determine the virial parameter per unit length along the filament and find that the highest mass protostars form in the most bound portion of the filament, as suggested by theoretical models.