Molecular Environments of Class II Methanol Masers

Abstract

This dissertation explores the environments of massive star forming regions traced by 6.7 GHz Class II methanol masers. This has been done using molecular line observations of a complete sample of 6.7 GHz Class II masers from the Methanol Multibeam survey. The lines used include the CS, 44 GHz Class I maser and NH$_3$ (1,1), (2,2) and (3,3) inversion transitions. Class I maser emission was detected toward 66\% of sources containing both CS and Class II maser emission. For sources containing NH$_3$ (1,1) and Class II maser emission 79 \% were found to have an associated Class I maser, with 89 \% detected in sources with NH$_3$ (2,2) emission and an increased Class I detection of 91 \% for sources with NH$_3$ (3,3) and Class II maser emission. This suggests that sources with NH$_3$ emission, and particularly those with NH$_3$ (3,3) emission are more likely to be associated with regions containing both Class I and Class II methanol masers.The average FWHM of the CS emission is found to be 4.3 kms$^{-1}$, the NH$_3$ (1,1), (2,2) and (3,3) transitions have line widths of 2.7 kms$^{-1}$, 3.1 kms$^{-1}$ and 4.6 kms$^{-1}$ respectively. The line widths of the NH$_3$ (1,1) emission suggest that the sources are at an evolutionary stage between massive protostellar collapse and the initiation of an UCHII region. The line widths of the NH$_3$ (3,3) emission are considerably larger than those of the NH$_3$ (1,1). This cannot be attributed solely to thermal broadening and may be indicating greater turbulence or more NH$_3$ (3,3) sub-structure along the line of sight. The sources with detected NH$_3$ (3,3) emission appear to be more turbulent than those sources without a NH$_3$ (3,3) detection.

Date of Award	1 Aug 2012
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Gary Fuller (Supervisor)