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A Search for Low Surface Brightness Dwarf Galaxies in Different Environments

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A Search for Low Surface Brightness Dwarf Galaxies in Different Environments A search for low surface brightness dwarf galaxies in different environments. by Sarah Roberts A thesis submitted to Cardiff University for the degree of Doctor of Philosophy 2005 UMI Number: U584747 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI U584747 Published by ProQuest LLC 2013. Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 DECLARATION This work has not previously been accepted in substance for any degree and is not being concurrently submitted in candidature for any degree. Signed Date ... STATEMENT 1 The work presented in this thesis is all my own work carried out under the super­ vision of Dr. Jonathan Davies with the exception of the following: the detection algorithm was provided to me by Sabina Sabatini and the optical MGS field data was taken by Liske et al. (2003). D a te . ± . ! l Z . Q £ . STATEMENT 2 I hereby give consent for my thesis, if accepted, to be available for photocopying and for inter-library loan, and for the title and summary to be made available to outside organisations. Signed D a te .^1....!.?:... ACKNOWLEDGEMENTS There are lots of people I have to thank in this thesis, both for their academic and thier personal support. My biggest thanks goes to Dr. Jon Davies, my PhD supervisor. He has helped, encouraged,ad vised, pushed and prodded me throughout my PhD, and I owe him quite a few beers for it! He was the best supervisor a student could ask for, and I really do count myself lucky to have been his student - Diolch yn fawr Jon! Next I’d like to thank my officemates for making coming into Uni so enjoyable! Thanks Simon for your mischevious sense of humour, knowledge of all things astronomi­ cal, and endless supply of chewing gum! Thanks Robbie for your words of HI wisdom, for reading through my thesis and helping make it so much better, and also for the relaxing games of Keyball! Rory - thanks for making our observing trip much more entertaining with your musical and table-tennis talents! Also, not forgetting my old office mate and friend, Sabina, who, when I first started my PhD, was always there to help me out with whatever problems or questions I had, no matter how busy she was at the time. Grazie Sabina! I also have to thank the gang from the Terminal room - Kris and Tim for their help when I needed it, and Dave and Hannah for their help with all my computing questions. You have the patience of Saints! (Thanks also for the duelling pistols!!) Also, thanks to Gustav for helping me out with all my statistics and programming problems - tack sa mycket for alltig Gustav! And Haley, thank you so much for reading through my thesis at the end - I’m sure you had better things to do with your time! You’re a seren! A big thanks also to Paul Roche for giving me a job whilst I was writing up, which meant that I could afford to buy food and pay my rent! And thanks to Edward, Fraser and Dave for keeping me amused and unstressed towards the end of my thesis writing - you're great workmates to be sure! To Wing I’d like to say a massive ‘xie xie’ for all your support and encouragement whilst I was finishing this thesis. You really did help me through it. Wo ai ni. Finally, I’d like to thank my brothers, Huw and Gwyn, and my parents for all their encouragement throughout my PhD. To mum and dad especially - thank you for everything. I can finally do what you keep telling me to do and relax! To mum and dad ABSTRACT Current theories of large scale structure and galaxy formation predict the existence of numerous low mass dark matter haloes in the Universe today. If these haloes contain sufficient stars they should be detectable as low luminosity stellar systems or dwarf galaxies. We have searched for these objects in four regions of increasing density - the general field, the area around a giant spiral galaxy, the low density Ursa Major cluster, and the high density Virgo cluster. Using identical deep optical data covering a total of 60°2 and probing fainter magnitudes than has been done previously, we used identical selec­ tion and detection methods to compare the dwarf galaxy populations in these different environments. We found substantially more dwarfs per giant galaxy in the Virgo cluster (~20:1) compared to the field environment (6:1 max). A comparison of the HI properties and (B-I) colours for the objects for which we had additional data also showed that in general, the cluster objects axe redder and gas poor compared to the objects in the field. We discuss the possible mechanisms which may have resulted in creating a pop­ ulation of cluster dwarf galaxies, which would explain the high number density which we found in our data. It is likely that a combination of tidal interactions and transfor­ mation of infalling dlrrs into dEs will result in the large population of cluster dwarfs. Conclusive evidence regarding their formation must now be obtained by a more detailed investigation of their stellar populations. The lack of dwarf galaxies in the field region is likely to be due to the effect of inefficient star formation in the field environment compared to the cluster. Thus the low mass dark matter haloes predicted by CDM models must still be ‘dark’ and can only be identified by further deep HI studies of the field environment, and future gravitational lensing studies of substructure. Contents 1 Introduction 1 1.1 The beginnings of Extra-galactic Astronomy ....................................... 1 1.2 The Galaxy Luminosity Function .......................................................... 3 1.3 Dwarf galaxy populations: Theory vs.Observations ............................. 8 1.3.1 T h eo ry .............................................................................................. 8 1.3.2 Observations ................................................................................. 23 1.3.3 Feedback mechanisms .................................................................... 29 1.4 Summary .................................................................................................... 37 2 The Environments 41 2.1 Virgo cluster ................................................................................................. 41 2.2 UMa c lu s te r................................................................................................. 48 2.3 Field - The Millennium Galaxy S t r i p .................................................... 54 2.4 M 101.............................................................................................................. 56 2.4.1 Area covered by our da ta ............................................................... 58 2.5 S u m m a ry .................................................................................................... 59 3 D ata 63 i ii___________________________________________________________ CONTENTS 3.1 Introduction ............................................................................................... 63 3.2 Instruments - optical ............................................................................... 65 3.2.1 Wide Field S u rv e y ...................................................................... 65 3.2.2 SDSS............................................................................................... 70 3.3 Instruments - HI ..................................................................................... 70 3.3.1 A re c ib o ......................................................................................... 70 3.3.2 HI Jodrell All Sky Survey (HIJASS) ...................................... 72 3.4 Summary .................................................................................................. 73 3.4.1 Optical d a ta ................................................................................... 73 3.4.2 HI d a t a ......................................................................................... 74 4 Detection and Selection 75 4.1 The Optical Detection Algorithm .......................................................... 77 4.1.1 Background fluctuation flattening ............................................. 77 4.1.2 Removal of other astronomical objects e.g. stars, bright galaxies, etc ..................................................................................... 78 4.1.3 Convolution of image with specifically designed filters .... 80 4.1.4 Classification of candidates .......................................................... 82 4.1.5 Application of selection c r ite r ia ................................................ 83 4.1.6 Eye-ball confirmation ................................................................... 83 4.2 Optical Selection Criteria ......................................................................... 84 4.2.1 Original sim ulation ...................................................................... 84 4.2.2 Influence of seeing ...................................................................... 90 CONTENTS ___________________________________________________________ hi 4.3 HI Detection and Selection.......................................................................
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