Paul Ruffle at Starry Night
PhD Thesis

The effects of dust grains in two dissimilar regions at opposite ends of the Milky Way

A thesis submitted to The University of Manchester for the degree of
Doctor of Philosophy
in the Faculty of Engineering and Physical Sciences

2006

Paul Ruffle
School of Physics and Astronomy

I examine the detected effects of dust grains in two dissimilar regions at opposite ends of the Milky Way: firstly in explaining anomalous extinction values towards the Galactic bulge through observations of Planetary Nebulae (PNe); and secondly in explaining the apparent photon-dominated regions (PDRs) observed in metal-poor molecular clouds at the Galactic edge. Angular diameters, fluxes and extinction of compact PNe are derived from observations, providing evidence for steeper extinction towards the Bulge. I suggest that for the inner Galaxy the low-density warm ionized medium is the site of the anomalous extinction, and that low values of extinction can also be derived using dust models with a turnover radius of 0.08 microns. I then go on to examine the chemistry of Edge Clouds 1 and 2 (EC1 & EC2), molecular clouds with the largest galactocentric distances in the Milky Way. I present observations of both clouds and these are used to determine their physical characteristics. Chemical models are used to reproduce the abundances in EC2 and they indicate: heavy elements may be reduced by a factor of five relative to the solar neighbourhood; very low extinction due to a high gas to dust ratio; an enhanced cosmic ray ionisation rate; and a high UV field compared to local interstellar values. Observed high abundances of the radicals C2H and CN are typical of PDRs, but at the Galactic edge, metal abundances are expected to be much reduced. In addition, although EC2 does contain young stars, there is no evidence of the late-type stars which produce dust grains, thereby justifying the assumption of a high ratio of UV flux to grain surface area. Finally, I note that shocks from an old supernova remnant may be the source of the structure and dynamics observed in EC2.

Downloadable PDFsContentsPage
Complete ThesisComplete 380 page document (14 MB)1
Contents, Abstract, etcAbstract7
Declaration8
Copyright Statement9
Dedication11
Acknowledgements12
The Author14
Supporting Publications15
Chapter 1Our Dusty Universe17
Part I: Chapters 2-7Determination of extinction towards the Galactic bulge25
Chapter 2Planetary Nebulae27
2.1Overview27
2.2Introduction28
2.3Observations and data processing32
2.4Filter wavelength shift with angle of incidence41
Chapter 3PNe Diameter Determinations43
3.1Method43
3.2Image restoration45
3.3Results49
3.4Discussion52
Chapter 4PNe Flux Determinations63
4.1Method63
4.2Results and error factors68
Chapter 5PNe Extinction Determinations77
5.1Theory77
5.2Method I80
5.3Method II82
5.4Brightness temperature83
5.5Results84
Chapter 6Discussion: Extinction91
6.1Evidence for anomalous extinction91
6.2Extinction and the warm ionized medium94
6.3Grain sizes96
Chapter 7PNe Conclusions99
7.1Angular diameters99
7.2Fluxes99
7.3Extinction100
7.4Further work101
Part II: Chapters 8-13Metal-poor molecular gas in Galactic edge clouds103
Chapter 8Galactic Edge Clouds105
8.1Overview105
8.2Introduction106
8.3Spectral line observations of EC2114
8.2Spectral line observations of EC1122
8.5Spectral line data reduction129
8.6Spectral line mapping of EC2132
8.7Dust mapping of EC2 and EC1137
Chapter 9Analysis of EC2 Observations141
9.1Beam deconvolution141
9.2Ammonia as a thermometer143
9.3Determination of temperature147
9.4Determination of density148
9.5Determination of molecular abundances153
9.6Determination of dust to gas ratio and mass157
Chapter 10Analysis of EC1 Observations163
10.1Summary163
Chapter 11Molecular Cloud Comparisons167
11.1Molecular abundances relative to HCO+167
11.2Molecular abundances relative to H2168
11.3Comparison with local molecular clouds168
11.4Comparison with translucent clouds169
11.5Comparison of EC1 with EC2169
Chapter 12Chemical Modelling of EC2173
12.1Method173
12.2Results175
12.3Fractional abundances over time181
Chapter 13Edge Cloud Conclusions199
13.1Edge Cloud 2199
13.2Edge Cloud 1203
13.3Further edge cloud work204
Part III: Appendices A-O Appendices205
Appendix AAdditional PNe image plots207
Appendix BEC2 map observations at the JCMT 15m telescope May-July 2005211
Appendix CEC2 observations at the ARO 12m telescope February - June 2002233
Appendix DEC2 observations at the ARO 12m telescope Nov 2002 & Feb 2003241
Appendix EEC2 observations at the ARO 12m telescope April 2004247
Appendix FEC2 observations at the JCMT 15m telescope June 2004251
Appendix GEC2 observations at the ARO 12m telescope Feb-Mar 2005255
Appendix HEC2 observations at the MPIfR 100m Dec 2002, May 2004, Nov 2005275
Appendix IEC2 observations at the ARO 12m telescope Dec 2005 - Jan 2006281
Appendix JEC1 observations at the ARO 12m telescope April 2004293
Appendix KEC1 observations at the ARO 12m telescope March 2005317
Appendix LEC1 observations at the OSO 20m telescope May 2005335
Appendix MEC1 observations at the MPIfR 100m telescope Oct-Nov 2005341
Appendix NPermanent electric dipole moments345
Appendix OEC2 Chemical Model Results349
List of FiguresList of Figures359
List of TablesList of Tables367
ReferencesReferences371
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