A molecular line and continuum study of water maser sources

Change log
Jenness, Timothy 

Recent observations at the James Clerk Maxwell Telescope (JCMT) and elsewhere have identified a class of very deeply embedded, possibly protostellar, sources which are not associated with any of the traditional indicators of star formation, such as HII regions and near-infrared emission, but which do lie close to otherwise isolated H2O masers.

This thesis describes a search, based on catalogues of known water maser positions, for new deeply embedded cores similar to those found in S106 and M17. In addition to millimetre molecular line and submillimetre continuum observations, 22 GHz and 8 GHz radio observations have been made of a number of the sources in order to obtain more accurate maser positions and to search for any associated compact HII regions. Observing sources such as these in less active star forming regions provides a cleaner environment in which to examine the maser excitation and the ongoing process of star formation.

A sample of 44 water maser sources was observed from which submillimetre continuum emission was detected from 40 (91 per cent). The most striking feature of the data is the close association of the masers with the submillimetre cores: the data are consistent with masers occurring within 6000 AU of the embedded core. The results can be summarised as follows:

o High temperature gas has been detected, and most of the submillimetre cores have mean densities greater than 10^6 /cm^3.

o The masers have low velocities with respect to the molecular cloud and are uniformly distributed within 6600 AU of the submillimetre core.

o The isotropic maser luminosity is proportional to the far-infrared luminosity over more than 5 orders of magnitude.

o There is no obvious correlation between the near-infrared spectral class and the maser emission.

o Where a radio spectral index is known the majority of sources are optically thin HII regions. The bulk of the remainder are undetected and have a flux density less than 1 mJy.

o Masers not associated directly with a submillimetre core show explicit evidence for shocks.

Embedded cores \emph{have} been detected with this survey and the maser emission is consistent with collisionally excited pump models.

astronomy, facilities: James Clerk Maxwell Telescope, water masers, star formation
Doctor of Philosophy (PhD)
Awarding Institution
University of Cambridge