Ian Stephens (BU)

Ian Stephens colloquium --MALT90 and Interferometric Observations of High-Mass Star-Forming Clumps with Unusua

Marsfield Lecture Theatre

Abstract

The Millimeter Astronomy Legacy Team 90 GHz (MALT90) survey
has detected high-mass star-forming clumps with “anomalous”
N2H+/HCO+(1-0) integrated intensity ratios that are either unusually
high (“N2H+ rich”) or unusually low (“N2H+ poor”). With 3 mm
observations from the Australia Telescope Compact Array (ATCA), we
imaged two N2H+ rich clumps, G333.234-0.061 and G345.144-00.216, and
two N2H+ poor clumps, G351.409+00.567 and G353.229+00.672. In these
clumps, the N2H+ rich anomalies arise from extreme self-absorption of
the HCO+ line. G333.234-0.061 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. Unexpectedly, the higher mass
core is at an earlier evolutionary stage than the lower mass core,
which may suggest that two different epochs of high-mass star
formation can occur in close proximity. Through careful analysis of
the ATCA observations and MALT90 clumps (especially the G333, NGC
6334, and NGC 6357 star formation regions), we find that N2H+ poor
anomalies arise at clump-scales and is caused by lower relative
abundances of N2H+ due to the distinct chemistry of H II regions or
photodissociation regions.