Physical and chemical conditions in methanol maser selected hot-cores and UCHII regions

Abstract

We present the results of a targeted 3-mm spectral line survey towards the eighty-three 6.67 GHz methanol maser selected star forming clumps observed by Purcell et al. 2006. In addition to the previously reported measurements of HCO+ (1 - 0), H13CO+ (1 - 0), and CH3CN (5 - 4) & (6 -5), we used the Mopra antenna to detect emission lines of N2H+ (1 - 0), HCN (1 - 0) and HNC (1 - 0) towards 82/83 clumps (99 per cent), and CH3OH (2 - 1) towards 78/83 clumps (94 per cent). The molecular line data have been used to derive virial and LTE masses, rotational temperatures and chemical abundances in the clumps, and these properties have been compared between sub-samples associated with different indicators of evolution. The greatest differences are found between clumps associated with 8.6 GHz radio emission, indicating the presence of an Ultra-Compact HII region, and `isolated' masers (without associated radio emission), and between clumps exhibiting CH3CN emission and those without. In particular, thermal CH3OH is found to be brighter and more abundant in Ultra-Compact HII (UCHII) regions and in sources with detected CH3CN, and may constitute a crude molecular clock in single dish observations. Clumps associated with 8.6 GHz radio emission tend to be more massive and more luminous than clumps without radio emission. This is likely because the most massive clumps evolve so rapidly that a Hyper-Compact HII or UCHII region is the first visible tracer of star-formation. The gas-mass to sub-mm/IR luminosity relation for the combined sample was found to be L proportional to M**0.68, considerably shallower than expected for massive main-sequence stars.

References in corpus (2)

• Multi-wavelength observations of Southern Hot Molecular Cores traced by methanol masers - I. Ammonia and 24 GHz Continuum Data
• Physical and chemical conditions in methanol maser selected hot-cores and UCHII regions

Cited by in corpus (7)

• The Onset of Massive Star Formation: The Evolution of Temperature and Density Structure in an Infrared Dark Cloud
• Physical and chemical conditions in methanol maser selected hot-cores and UCHII regions
• VLA Survey of Dense Gas in Extended Green Objects: Prevalence of 25 GHz Methanol Masers
• Observations of Cyanopolyynes toward Four High-Mass Star-Forming Regions Containing Hot Cores
• Chemical evolution of Red MSX Sources in the southern sky
• New detections of HC${}_5$N toward hot cores associated with 6.7 GHz methanol masers
• Chemical evolution of N2H+ in six massive star-forming regions