HI in the M31/M33 Environment A thesis presented to the faculty of the College of Arts and Sciences of Ohio University In partial fulfillment of the requirements for the degree Master of Science Nicole L. Free November 2010 © 2010 Nicole L. Free. All Rights Reserved. 2 This thesis titled HI in the M31/M33 Environment by NICOLE L. FREE has been approved for the Department of Physics and Astronomy and the College of Arts and Sciences by Felix J. Lockman Adjunct Professor of Physics and Astronomy Joseph C. Shields Professor of Physics and Astronomy Benjamin M. Ogles Dean, College of Arts and Sciences 3 ABSTRACT FREE, NICOLE L., M.S., November 2010, Physics and Astronomy HI in the M31/M33 Environment (70 pp.) Director of Thesis: Felix J. Lockman and Joseph C. Shields With recent debate about a reported neutral hydrogen, HI, streamer between M33 and M31, we set out to determine the existence of the HI streamer. Using the National Radio Astronomy Observatory’s 100 m Green Bank Telescope, with 9.1´ angular resolution, we mapped the HI in the region from Wright’s Cloud and M33 through the location of the streamer features, as reported by Braun and Thilker (2004). To verify the findings of Braun and Thilker, we also performed pointed observations at two of the three local maxima within their maps. From our observations, we were able to confirm the existence of the three local maxima points. The three features have column densities ranging from 2.3 to 5.4 , with most being of the order of magnitude of the latter. The masses of the features range from 6.6 to 2.2 . All of the features appear to have more structure and be more compact than previously thought. After examining the Wright’s Cloud region to determine if there was any comparable Galactic HI in the region, it was found that these features are inconsistent with the Galactic High Velocity Clouds in the area of observation. Though the origin of the streamer features cannot concretely be set, with the Pan-Andromeda Archeological Survey’s (PAndAS) findings of optical evidence of recent interaction between M33 and M31, the origin of the features from such an interaction remains probable. 4 Approved: _____________________________________________________________ Felix J. Lockman Adjunct Professor of Physics and Astronomy Approved: _____________________________________________________________ Joseph C. Shields Professor of Physics and Astronomy 5 ACKNOWLEDGMENTS I would like to express my heartfelt thanks to all those who have helped and supported me through the completion of this thesis. My advisors Joseph Shields and Jay Lockman for their guidance and encouragement. The other members of my committee, Nancy Sandler and Kenneth Hicks, for their guidance. Don Roth, without whom I would probable still be working out some computer problems. The National Radio Astronomy Observatory and the Department of Physics and Astronomy at Ohio University for my financial support. All of my wonderful classmates and fellow astronomy students for their friendship and assistance. Chris and Kate Willis, my dear friends, for their continued love, support, and understanding. Heath Kersell for his love and friendship which have brought joy to even the longest homework assignments. My family, Dwight Free, Mary Ann Wisherd, and Bill and Colleen Grissom for their love, guidance, and continual encouragement. Natalie Free, my beloved sister, whose love and support are one of the greatest blessings in my life. My late grandmother, Phyllis Wilt, for her love, support, and never ceasing belief in me. To the Lord God for His steadfast love. 6 TABLE OF CONTENTS Page Abstract ............................................................................................................................... 3 Acknowledgments............................................................................................................... 5 List of Tables ...................................................................................................................... 8 List of Figures ..................................................................................................................... 9 Chapter 1: Introduction ..................................................................................................... 10 1.1 21 Centimeter Neutral Hydrogen ...................................................................... 12 1.2 High Velocity Clouds ....................................................................................... 14 1.3 The Magellanic Stream ..................................................................................... 16 1.4 Wright’s Cloud ................................................................................................. 19 1.5 M33 ................................................................................................................... 20 Chapter 2: Observations and Data Reduction ................................................................... 27 2.1 Observations ..................................................................................................... 27 2.1.1 Pointed Observations ....................................................................................... 27 2.1.2 Maps ................................................................................................................. 28 2.2 Data Reduction ................................................................................................. 31 2.2.1 GBTIDL ........................................................................................................... 33 2.2.2 IdlToSdfits ....................................................................................................... 34 2.2.3 AIPS ................................................................................................................. 34 2.2.4 Python .............................................................................................................. 35 2.2.5 CASA ............................................................................................................... 37 Chapter 3: Results and Discussions .................................................................................. 38 3.1 Analytical Tools and Procedure ........................................................................ 38 3.2 Completeness of Study ..................................................................................... 40 3.2.1 Velocity ............................................................................................................ 40 3.2.2 Position ............................................................................................................ 40 3.2.3 HI Column Density and Mass .......................................................................... 41 3.3 M31/M33 Stream .............................................................................................. 42 3.3.1 Braun I ............................................................................................................. 46 7 3.3.2 Braun II ............................................................................................................ 50 3.3.3 Braun III ........................................................................................................... 53 Chapter 4: Conclusions ..................................................................................................... 55 4.1 Milky Way High Velocity Clouds .................................................................... 55 4.2 High Velocity Clouds Originating from M31 ................................................... 56 4.3 Association with M31 Dwarf Galaxies ............................................................. 56 4.4 M31/M33 HI Stream ......................................................................................... 57 4.5 Future Considerations ....................................................................................... 58 References ......................................................................................................................... 60 Appendix: Automatic Residual Instrumental Baseline Removal Python Script .............. 63 8 LIST OF TABLES Page Table 1: Characteristics of M33, M31, AND I, and AND XV ………………………...... 22 Table 2: Distance Between M31/M33 Stream Elements and Local Group Galaxies … 22 Table 3: NHI and MHI Sensitivity Limits ……………………………………………… 41 Table 4 A: M31/M33 Stream Features ………………………………………...…….... 42 Table 4 B: Continuation of M31/M33 Stream Features …………………………...….. 43 Table 4 C: Continuation of M31/M33 Stream Features ……………………...……….. 44 Table 4 D: Continuation of M31/M33 Stream Features …...………………………….. 45 9 LIST OF FIGURES Page Figure 1: Optical and Radio Image of the M81 System ................................................ 13 Figure 2: Magellanic System ......................................................................................... 17 Figure 3: Filaments and CHVCs of the Magellanic Stream .......................................... 19 Figure 4: Braun and Thilker (2004) HI Survey Map ..................................................... 23 Figure 5: Putman et al. (2009) M33 HI Map ................................................................. 24 Figure 6: PAndAS Survey Map ………………………………………………………. 25 Figure 7: PAndAS Map With Newly Discovered Dwarf Galaxies …....……………... 26 Figure 8: Gridding Regions and Locations of Pointed Observations ………………… 30 Figure 9: Green Bank Telescope …………..……….……………………………..….. 32 Figure 10: Diagram