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A Search for Dark Galaxies Through the AGES

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A Search for Dark Galaxies Through the AGES A search for dark galaxies through the AGES by Robbie Richard Auld A thesis submitted to Cardiff University for the degree of Doctor of Philosophy May 2007 UMI Number: U584983 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 U584983 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 coi ' * ndidature for any degree. Signed Date STATEMENT 1 The work presented in this thesis is all my own work carried out under the joint supervision of Dr. J. I. Davies and Dr. W. J. G. de Blok, with the exception of the following: I did not take the optical, NIR, Ha, or HI observations for Chapter 2, although all subsequent data reduction and analysis is my own. The optical, NIR, and Ha data were kindly made available by Dr. Eric Bell. Dr. W. J. G. de Blok took the HI observations. The optical spectroscopy data from Loiano, presented ced by Dr. L. Cortese. 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. ACKNOWLEDGMENTS Jane, for all your support and love during our difficult time apart, thank you. You have always been there for me, thank you so much. And thank you for being so patient with me during my lengthy writing-up period. I love you. Mum and Dad, thanks for all your love and ’where’s the thesis?’ support. Thanks also to Jon and Erwin for your guidance, advice and free drinks throughout the three years. Without your support and tutelage I would not have made it this fax. I feel privileged to have worked with you both and hope that this thesis does you both justice. Thanks to the other members of the group; Diego, Luca, Marco, Mike, Rhodri, Rhys, Rory, Sabina & Sarah for some very entertaining group meetings and discussions. Thanks also to my officemates, Simon, Luca and Rory for enduring my endless questions and terrible jokes. Finally, thanks to everyone else who’ve helped me enjoy my time in the department (and in the pub); James, Bruce, Mike Z., Gustav, Tim, Rich, Pete, Rhianne, Dave, Dimitris and everyone else. This research makes use of data taken with the 305 m radio telescope at Arecibo, Puerto Rico. The Arecibo Observatory is part of the National Astronomy and Ionoshpere Cen­ tre, which is operated by Cornell University under a cooperative agreement with the National Science Foundation. This research makes use of data taken with The Australian Telescope Compact Array. The Compact Array is part of the Australian Telescope National Facility (ATNF). ATNF is funded by the Commonwealth of Asutralia for operations as a national facility managed by CSIRO. This research makes use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research also makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. ABSTRACT The work I have performed for this thesis covers a number of different areas of astronomy. My work on the LSBs is an in-depth exploration of the gas morphology and kinematics of these unusual objects. The focus is on the star forming abilities of the galaxy sample, but the HI observations also reveal a rich variety of gas morphology and motion, which are not necessarily apparent at other wavelengths. As well as being LSB, they are neutral gas-rich objects. As such they are more suited to being detected by HI surveys than by optical surveys. The Arecibo Galaxy Environment Survey (AGES) is a survey that expects to detect a large number of this type of galaxy and a large proportion of the thesis has been dedicated to my involvement with the survey. This has included designing and implementing the observing strategy, testing the data reduction pipeline, producing the final data, testing their quality and examining the efficiency of the survey detection methods. I have demonstrated some uses the AGES data can be put to; from discovering hitherto undetected galaxies, through measuring the cosmic distribution of neutral hydrogen, to evaluating the cosmic significance of dark galaxies. The last point forms the central theme throughout the thesis. Of the 69 detections made by AGES in the first two datacubes, 55 do not have previous Hi measurements and 26 are previously uncatalogued. An Hi mass function (HIMF) was produced from the first galaxies detected by AGES. The best fit line to the data was a Schechter function with the parameters: a = —1.28 it 0.17, = 0.0076 ± 0.0027 and M* = 7.7 it 1.8 x 109 M q . Using the HIMF the calculated value for the space density of neutral hydrogen was found to be pni = 7.5q3 x 1 0 7M q Mpc-3, which is consistent with previous measurements. The overall contribution of HI to the Universal energy density was calculated from this value and found to be VLhi = 4.1};3 x 10-4, confirming previous measurements of this value. Assuming the two candidates axe indeed optically dark, based on this value the contribu­ tion of dark galaxies was calculated to be 4% to their respective mass bins, and less than 0.5% overall. The number density was found to be ndark ~ 6-6 x 10-4 Mpc-3. Hence it would appear that dark galaxies are not numerous enough nor of substantial mass to be able to account for the ‘missing mass’ or to be able to fully represent the high number of dark matter haloes produced by CDM simulations. Contents 1 Introduction 1 1.1 General Properties of the Universe ...................................................... 1 1.2 Cold Dark M atter ..................................................................................... 6 1.3 Star Formation Thresholds ..................................................................... 13 1.3.1 The Toomre-Q Criterion ............................................................ 13 1.3.2 The Shear-modified Toomre-Q................................................... 16 1.3.3 Constant Hi star formation threshold ...................................... 17 1.4 Selection Effects ........................................................................................ 21 1.4.1 Low Surface Brightness Galaxies ............................................ 24 1.5 Hi Surveys .............................................................................................. 26 1.5.1 Radio Astronomy ........................................................................ 26 1.5.2 The 21-cm line of h y d ro g en ...................................................... 27 1.5.3 The Hi Mass Function ............................................................... 29 1.5.4 Single Beam HI S urv eys ............................................................ 31 1.5.5 Multibeam HI Surveys ................................................................ 34 1.6 Dark Galaxies........................................................................................... 40 i ii___________________________________________________________ CONTENTS 2 The conditions for star formation in LSBs 47 2.1 Introduction ................................................................................................ * 47 2.2 History of star formation thresholds in LSBs ...................................... 48 2.3 The galaxy s a m p le ................................................................................... 56 2.4 Observations and data reduction ............................................................ 57 2.4.1 R-band, 72-band and Ha d a t a .................................................... 57 2.4.2 A-band d a ta .................................................................................... 58 2.4.3 HI d a t a ........................................................................................... 59 2.5 Galaxy properties ...................................................................................... 61 2.5.1 Optical properties ........................................................................... 61 2.5.2 Hi morphology and d y n a m ics .................................................... 68 2.5.3 HI Rotation c u rv e s ....................................................................... 80 2.6 Combined HI and optical data ............................................................... 81 2.6.1 Mass-to-light ra tio s ....................................................................... 81 2.6.2 The Kennicutt Star Formation Threshold ................................. 83 2.6.3 The constant density star formation threshold ....................... 87 2.7 Discussion .................................................................................................. 89 2.8 C onclusions ..............................................................................................
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