by Ian Stephens (Boston University)

The Millimetre Astronomy Legacy Team 90 GHz (MALT90) Mopra survey has detected high-mass star-forming clumps with anomalous N ₂ H ⁺ /HCO ⁺ (1-0) integrated intensity ratios that are either unusually high (“N ₂ H ⁺ rich”) or unusually low (“N ₂ H ⁺ poor”). With 3 mm observations from the ATCA, two N ₂ H ⁺ rich clumps and two N ₂ H ⁺ poor clumps were imaged. In these clumps, the N ₂ H ⁺ rich anomalies arise from extreme self-absorption of the HCO ⁺ line. G333.234-00.061 (above) contains two of the most massive protostellar cores known with diameters of less than 0.1 pc, separated by a projected distance of only 0.12 pc. The white contours and the blue color scale show the 3 mm continuum, blue contours show the 8 micron Spitzer IRAC emission, and the X symbols mark locations of many different types of masers. These extreme self-absorbed high-mass star-forming clumps observed with Mopra may indicate the locations of the most massive star-forming sites.