Physics
Scientific paper
Dec 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt.........9t&link_type=abstract
PhD Thesis, Department of Physics, Queen Mary and Westfield College, University of London, UK, 1999.
Physics
5
Scientific paper
The vast majority of star formation occurs in regions dominated by high-mass stars, such as the Orion complex. Through their hii regions, these massive stars profoundly affect the surrounding molecular gas, and quite probably trigger further star formation. This thesis presents the results of a submillimetre study of the interface between the Lagoon Nebula, M8, a large hii region in the southern hemisphere, and its associated molecular cloud. Continuum maps of M8 were obtained at wavelengths of 450 microns and 850 microns with SCUBA on the JCMT, and at 1.3 mm with the MPIfR 37-channel array at IRAM. A new subroutine was added to the data reduction facility for SCUBA (SURF); when skydip data are analysed to calculate the atmospheric opacity, this subroutine estimates the error in the fitted opacity. The performance of the subroutine is discussed, based on the M8 map data. The continuum maps are analysed by fitting gaussian profiles to the clumpy structure (on the 0.1 pc scale). Discrepancies between the fitted profiles at different wavelengths suggest that there are very considerable errors in this fitting process. There are a number of possible sources of contamination of the continuum emission, both non-thermal (free-free emission and molecular line emission) and thermal (greybody emission from hotter dust associated with the hii region and PDRs on the surfaces of the clumps). The likely magnitude of contamination from these sources is assessed: Line contamination is likely to be the largest, comprising between 10% and 50% of the detected continuum flux. The greybody emission from PDRs is likely to be in the range 10--20%. The other sources of contamination are unlikely to be larger than the calibration error (~10%). Partial maps of the Lagoon Nebula were obtained at the JCMT in the J = 3-2 transitions of various isotopomers of CO. These data are used to estimate the temperatures of the clumps, and to estimate their densities independently of the continuum emission. Using the gas temperatures to estimate the dust temperatures in the clumps, the mean empirical emissivity index, m, is estimated to be 1.4+/- 0.3. Taking into account the likely effect of molecular line contamination, the underlying dust emissivity index, β, is estimated to be 1.7+/- 0.5. The clump masses are estimated from continuum fluxes; above about 6 Modot, the clump mass spectrum can be fitted by a power-law: dN/dM ~ M-α, where α≅ 1.66+/- 0.45. The power-law index is found using Kolmogorov-Smirnov (KS) statistics, and the confidence interval of the index is estimated by Monte Carlo resampling and KS statistics. This determination is consistent with other studies on similar spatial scales using molecular line tracers, but is not consistent with recent studies at smaller scales using continuum emission as a tracer. This suggests firstly that molecular and continuum determinations of clump mass spectra are in agreement, and secondly that the clump mass spectrum is not spatially scale-free. The likely evolution of the clumps, exposed to the UV field of massive stars, is discussed according to published analyses of similar structures. The external pressure on the clumps appears to be systematically higher than the internal pressure, suggesting that shock fronts have not yet penetrated the clumps. Despite large uncertainties in the mass estimates, the clumps seem to be gravitationally unstable, but it is not clear whether or not they can collapse before being photoevaporated by the UV field. The clumps are similar in nature to, but probably at an earlier stage of their evolution than, the `fingers' in the Eagle Nebula; the effects of the UV field may be eventually be sufficient to produce a new stellar generation in these structures.
No associations
LandOfFree
The Structure and Evolution of the Lagoon Nebula: Star Formation in the Sagittarius Arm does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The Structure and Evolution of the Lagoon Nebula: Star Formation in the Sagittarius Arm, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Structure and Evolution of the Lagoon Nebula: Star Formation in the Sagittarius Arm will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1583751