Paul Ruffle - PhD Thesis 2006

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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 PDFs	Contents	Page
Complete Thesis	Complete 380 page document (14 MB)	1
Contents, Abstract, etc	Abstract	7
	Declaration	8
	Copyright Statement	9
	Dedication	11
	Acknowledgements	12
	The Author	14
	Supporting Publications	15
Chapter 1	Our Dusty Universe	17
Part I: Chapters 2-7	Determination of extinction towards the Galactic bulge	25
Chapter 2	Planetary Nebulae	27
2.1	Overview	27
2.2	Introduction	28
2.3	Observations and data processing	32
2.4	Filter wavelength shift with angle of incidence	41
Chapter 3	PNe Diameter Determinations	43
3.1	Method	43
3.2	Image restoration	45
3.3	Results	49
3.4	Discussion	52
Chapter 4	PNe Flux Determinations	63
4.1	Method	63
4.2	Results and error factors	68
Chapter 5	PNe Extinction Determinations	77
5.1	Theory	77
5.2	Method I	80
5.3	Method II	82
5.4	Brightness temperature	83
5.5	Results	84
Chapter 6	Discussion: Extinction	91
6.1	Evidence for anomalous extinction	91
6.2	Extinction and the warm ionized medium	94
6.3	Grain sizes	96
Chapter 7	PNe Conclusions	99
7.1	Angular diameters	99
7.2	Fluxes	99
7.3	Extinction	100
7.4	Further work	101
Part II: Chapters 8-13	Metal-poor molecular gas in Galactic edge clouds	103
Chapter 8	Galactic Edge Clouds	105
8.1	Overview	105
8.2	Introduction	106
8.3	Spectral line observations of EC2	114
8.2	Spectral line observations of EC1	122
8.5	Spectral line data reduction	129
8.6	Spectral line mapping of EC2	132
8.7	Dust mapping of EC2 and EC1	137
Chapter 9	Analysis of EC2 Observations	141
9.1	Beam deconvolution	141
9.2	Ammonia as a thermometer	143
9.3	Determination of temperature	147
9.4	Determination of density	148
9.5	Determination of molecular abundances	153
9.6	Determination of dust to gas ratio and mass	157
Chapter 10	Analysis of EC1 Observations	163
10.1	Summary	163
Chapter 11	Molecular Cloud Comparisons	167
11.1	Molecular abundances relative to HCO+	167
11.2	Molecular abundances relative to H2	168
11.3	Comparison with local molecular clouds	168
11.4	Comparison with translucent clouds	169
11.5	Comparison of EC1 with EC2	169
Chapter 12	Chemical Modelling of EC2	173
12.1	Method	173
12.2	Results	175
12.3	Fractional abundances over time	181
Chapter 13	Edge Cloud Conclusions	199
13.1	Edge Cloud 2	199
13.2	Edge Cloud 1	203
13.3	Further edge cloud work	204
Part III: Appendices A-O	Appendices	205
Appendix A	Additional PNe image plots	207
Appendix B	EC2 map observations at the JCMT 15m telescope May-July 2005	211
Appendix C	EC2 observations at the ARO 12m telescope February - June 2002	233
Appendix D	EC2 observations at the ARO 12m telescope Nov 2002 & Feb 2003	241
Appendix E	EC2 observations at the ARO 12m telescope April 2004	247
Appendix F	EC2 observations at the JCMT 15m telescope June 2004	251
Appendix G	EC2 observations at the ARO 12m telescope Feb-Mar 2005	255
Appendix H	EC2 observations at the MPIfR 100m Dec 2002, May 2004, Nov 2005	275
Appendix I	EC2 observations at the ARO 12m telescope Dec 2005 - Jan 2006	281
Appendix J	EC1 observations at the ARO 12m telescope April 2004	293
Appendix K	EC1 observations at the ARO 12m telescope March 2005	317
Appendix L	EC1 observations at the OSO 20m telescope May 2005	335
Appendix M	EC1 observations at the MPIfR 100m telescope Oct-Nov 2005	341
Appendix N	Permanent electric dipole moments	345
Appendix O	EC2 Chemical Model Results	349
List of Figures	List of Figures	359
List of Tables	List of Tables	367
References	References	371

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