Formaldehyde Observations Towards Methanol Maser Sources.
ABSTRACT
Observational works on 4.83 GHz Formaldehyde (H2CO) absorptions and 4.87 GHz H110α radio recombination lines towards 6.7 GHz Methanol (CH3OH) maser sources are presented.
Methanol masers provide ideal sites to probe the earliest stages of massive star formation, while 4.8 GHz Formaldehyde absorptions are accurate probes of physical conditions in dense and low temperature molecular clouds towards massive star forming regions.
Feature similarities between the formaldehyde absorptions and the methanol masers are studied to expand knowledge of events and physical conditions in massive star forming regions.
A total of 176 methanol maser sources were observed for formaldehyde absorptions, and detections were made in 138 of them (corresponding to a detection rate of about 80%). Fifty-three of the formaldehyde absorptions are new discoveries.
We observed strong correlation (r=0.89, ρ=3.78 × 10-47) between the formaldehyde and methanol source velocities, but a weak correlation (r=-0.03, ρ=0.72) between their intensities.
This possibly indicates that the signals arise from about the same regions, but that the mechanisms that enhance their excitations are different.
The strongest formaldehyde absorptions were associated with IRAS (Infrared Astronomical Satellite) sources and IRDCs (Infra-Red Dark Clouds) that have developed HII regions, and that do not have EGOs (Extended Green Objects).
TABLE OF CONTENTS
Certification
Declaration
Acknowledgements
Abstract
Table of Contents
List of Figures
List of Tables
Chapter 1: Introduction
1.1 A General Introduction to Masers….1
1.2 Astrophysical Masers ………2
1.3 Formaldehyde Absorptions and Methanol Masers ….3
1.4 Purpose of Study ………5
Chapter 2: Literature Review
2.1 Association of Formaldehyde Absorptions with Massive Star Forming Regions …..6
2.2 Kinematic Distance Ambiguity Resolutions using Formaldehyde Absorptions ….7
2.3 Observations of Formaldehyde Absorptions ……8
2.4 EGOs and IRDCs ………… 11
Chapter 3: Observations, Analysis and Results
3.1 Observations ……… 13
3.2 Analysis of Data …… 14
3.2.1 GILDAS Commands and Proceedures for Analysis of the Data .. 14
3.2.2 Illustrations of the Line Parameters on Spectral Images …. 17
3.3 Results …. 19
3.4 Resolution of Kinematic Distance Ambiguities ………….. 35
Chapter 4: A Machine Learning Approach
4.1 An Introduction to Machine Learning…. 38
4.2 Data Used … 38
4.3 Method Used ….. 40
4.3.1 The K-means Clustering Algorithm …. 40
4.3.2 Choosing the Number of Clusters in a given set of Observations …….. 41
4.4 Clusters Obtained and Discussions … 44
Chapter 5: Discussions and Conclusions
5.1 Methanol Maser Relations with Formaldehyde Absorptions .. 51
5.2 Other Massive Star Formation Region Tracers …….. 51
5.3 Conclusions and Recommendations for Future Work … 54
References
Appendix 61
INTRODUCTION
1.1 A General Introduction to Masers
The term ‘Maser’ was originally meant to be an acronym for Microwave Amplification by Stimulated Emission of Radiation, but advancements in technology has shifted the usage to encompass emissions from across the electromagnetic spectrum since emissions with frequencies other than in the microwave band (e.g, radio frequencies) have also been observed.
For the sake of this work, we present a brief explanation of the principle governing man-made (or artificial) masers, and then provide a more extended discussion on astrophysical masers, which are naturally occurring masers.
Artificial masers are produced in the laboratory by man for use or application in certain fields. The system basically involves the excitation, and subsequent de-excitation, of a series of atoms or molecules to generate the amplification of photons.
The expectation is that given any two energy levels, the number of molecules in the higher level should be less than the number in the lower level, but under exceptional conditions as discussed shortly, the reverse can be true, and a population inversion is said to exist between the two levels.
Atoms or molecules are excited to higher energy states when they absorb radiations of appropriate frequency corresponding to the energy difference between the energy states.
According to the principles of quantum mechanics, for an atom to be excited from a state with energy, say E1, to a state with energy, say E2, the photon it will absorb should have a frequency, f = (E2-E1)/h, where h is Planck’s constant.
REFERENCES
Anderson, L. D., Bania, T. M. 2009, ApJ, 690, 706
Araya, E., Hofner, P., Churchwell, E., Kurtz, S. 2002, ApJS, 138, 63
Araya, E., Hofner, P., Linz, H., Sewilo, M.,Watson, C., Churchwell, E., Olmi, L., Kurtz, S. 2004, ApJS, 154, 579
Araya, E., Hofner, P., Goss, W. M., Linz, H., Kurtz, S., Olmi, L. 2007, ApJSS, 170, 152 Ball, J. A., Gottlieb, C. A., Lilley, A. E., Radford, H. E. 1970, ApJ, 162, L203
Ball, N. M., Brunner, R. J., Myers, A. D. 2008, ASP Conference Series, 394
Banerji, M., Lahav, O., Lintott, C. J., Abdalla, F. B., Schawinski, K., Bamford, S. P., Beaumont, C., Goodman, A. A., Williams, J. P. 2011, AAS, 43, 217
Bartkiewicz, A., Langevelde, H. J. V. 2012, Proceedings IAU Symposium, 287, 1