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The Interstellar Medium the Edge-On Galaxies Ngc 3044

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The Interstellar Medium the Edge-On Galaxies Ngc 3044 THE INTERSTELLAR MEDIUM AND DISK-HALO INTERACTION OF THE EDGE-ON GALAXIES NGC 3044 AND NGC 5775 Siow-Wang Lee A t hesis presented to the Depart ment of P hysics in fulfilment of the reqiiirement for the degree of Doctor of Philosophy Kingston, Ontario, Canada, 1998 @ Siow-Wang Lee, 1998 Acquisitions and Acquisitions et Bibliogmphic Services services bibliographiques 395 Wellington Street 395, nie Wellington OttawaON K1A ON4 ômwa ON K1A ON4 Caneda Canade The author has granted a non- L'auteur a accordé une licence non exclusive licence aîlowing the exclusive permettant a la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or sel1 reproduire, prêter, distribuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la forme de microfiche/film, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fiom it Ni la these ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. Abstract This thesis studies the interstellu medium (ISM) and the disk-halo interaction of two spiral galaxies, NGC 3044 and NGC 5775. These two galaxies are both edge-on and infrared-bright, but NGC 3044 is isolated and NGC 5775 is currently interacting with a companion. We found HI supershells in both of these galaxies. The purpose of this study is to examine the different components of the ISM, to compare their distributions within each galaxy, to relate the ISM to the formation of supershells and to test the ISM disk-halo mode1 envisaged in Norman and Ikeuchi (1989). Such a comprehensive study of the ISM in galaxies known to host large-scale structures has never before been done. Our work therefore contributes to the understanding of the formation of these structures with respect to the global structure of the ISM. We have found large-scale vertical structures of neutral hydrogen gas emerging from the disk of both galaxies. We have obtained observational data which trace the distributions of the different components of the ISM, including emission from neutral hydrogen, molecular gas, energetic cosmic rays, dust and ionized gas. For both galaxies, we find normal global ISM parameters such as total mass, density, luminosity and star formation rate (SFR) for starburst galaxies of their class (SBc), in spite of the existence of a global asym- metry in the gas distribution in NGC 3044 and the current interaction of NGC 5775 wi t h its companion. This indicates that the formation of large-scale structures does not require extreme conditions, since these galaxies are normal by al1 account. We found expanding supershell signatures in 4 of the high latitude features in . 11 NGC 3044 and 2 in NGC 5775. Assuming a one time energy injection by supernovae at the centre of an expanding feature, most of the expanding features would require the equivalent of tens of thousands of supernovae. For both galaxies, we show that the current SFR and available Ha luminosity do not preclude the existence of supergiant star clusters that can produce this many supernovae. However, the largest super star clusters observed in some galaxies contain a factor of 2-3 less massive stars than required to form the largest supershells in the two galaxies study here. We suggest that assistance from instability of magnetic field lines rnay be necessary to alleviate the extreme energy requirements. For NGC 3044, the formation of supershells by impacting clouds rnay be ruled out based on the ages of the supershells and the lack of a source of high velocity clouds around the galaxy. For NGC 5775, at least 2 high-latitude features are related to the neutral hydrogen bridge connecting it with its interacting cornpanion. However, some of the other features strongly indicate an interna1 origin. For this galaxy, a combination of cloud impacts and massive stars may be working together to produce the high-latitude features observed. An ISM disk-halo interaction model proposed by Norman and Ikeuchi (1989) en- visages the ISM of a galaxy to be in one or more of three stages: the three-phase stage, in which hot gas fills the ISM; the Chimney stage in which hot gas fills only a srnall volume of ISM via the channels provided by the hollow and broken-topped supershells (the so-called Chimneys); and the two-phase stage in which the super- shells are not able to break out of the neutral gas layer. By constraining the degee of clumping of supernovae in OB associations and the ambient gas density, the model predicts that both galaxies are very likely to be in the Chimney phase, consistent with what we would infer from the fact that supershells are observed. iii Statement of Originality The contents of this thesis are solely the work of the author, under the supervision of Dr. Judith A. Irwin, except for the following: The '*CO J=1+0 data for NGC 5775 were obtained and reduced (but not analyzed) by Gotz Golla. The HI results were taken from Irwin (1994) with permission. The radio continuum results were obtained from Sorathia (1994) for NGC 3044 and Duric et al. (1997) for NGC 5775 with permission. The HIRES images were product of the Infrared Processing and Analysis Center (IPAC) in Pasadena California. The Ha images were supplied by R. Grashuis and N. Duric (for NGC 3044) and R.-J. Dettmar (for NGC 5775). Acknowledgment First and foremost 1 would like to thank my supervisor, Judith Irwin, whom 1 admire a great deal for her dedication, professionalism, encouragement, understanding and kindness. 1 have learned much from you, Judith, and not just in Astronomy. To my PhD cornmittee members, Dave Hanes, Lamy Widrow and Marsha Singh, my gratitude. To Dick Henriksen, thanks for your humour, it brightened my days! To Dr. Chia Tze Tit at the National University of Singapore for encouraging me to pursue this degree. 1 am deeply grateful to you. A big thank you to Kathy Perrett, my friend and office-mate, for her friendship, and most of al1 her accommodation and endurance in these last few months! It also gives me great pleasure to thank my friends Steve Butterworth, JJ Kavelaars, Ed Thommes, Qingqing Qiu, Annie Hsu, Denise King, Jayanne English, Brian Frei, Paul Miyagawa, Brian King and Noha Salem, amongst others. You made my stay in Kingston and Queen's so mernorable. Steve and JJ also helped me solve many computer related problems. 1 have also enjoyed the rnany fruitful discussions about Astronomy and other subjects with Denise and Jayanne. To al1 the staff members of the Physics Department, thank you for your help over the years. 1 would also like to express my sincere gratitude to the staff of the Joint Astronomy Centre and the Herzberg Institute of Astrophysics for their help in observing at the JCMT,in software support and data reductions. My appreciation to Dr. Gotz Golla, for giving me the 12C0 J=l-tO data for NGC 5775 from SEST and for your help in general. A special thanks goes to Marcia Knutt, rny good friend, for being there and for understanding me. 1 treasure our friendship. Finally, this thesis would not have been possible without the support (be it moral, scientific, cornputer or domestic!) of my husband, David Wing. 1 can not thank you enough, Dave. This research has made use of the NASA1/IPACZ Extragalactic Database which is operated by the Jet Propulsion Laboratory, Caltech, under contract with the National Aeronautics and Space Administration. This research has also made use of NASA's Astrophysics Data System Abstract Service. 1 would also like to acknowledge the National Research Council of Canada (NRC) for supporting my many observing trips. This research is made possible by the Natural Sciences and Engineering Research Council of Canada (NSERC) through the graduate student support. l National Aeronautics and Space Administration lhfrared Processing and Analysis Center Table of Contents Abstract Statement of Originality Acknowledgment v List of Tables xii List of Figures xiv Introduction 1 1.1 General Structure of the Intersteliar Medium . 1 1.2 Observational Evidence of Disk-Halo Interactions . 4 1.3 The Origin of Supershells - Two Popular Models . 7 1.3.1 Stellar Winds and Supernovae Explosions . 7 1.3.2 The Impacting Cloud Mode1 . 13 1.4 Summary and Discussion of This Project . 16 2 Observations and Data Reductions 19 2.1 HI Observations and Data Reduction . 19 2.2 CO Observations and Data Reduction . 20 2.2.1 Data Processing . 29 vii 2.2.2 Data Sampling .......................... 30 2.3 Radio Continuum Data .......................... 31 2.4 High Resolution Infrared Astronomical Satellite Data (HIRES) .... 37 2.5 The Ha Observations of NGC 3044 and NGC 5775 .......... 30 3 NGC 3044 3.1 Introduction ................................ 3.2 Observations ................................ 3.3 The HI Distribution in NGC 3044 .................... 3.3.1 The HI Channel Maps ...................... 3.3.2 The Column Density Maps .................... 3.3.3 The Velocity Field ........................ 3.3.4 The HI Global Profile ...................... 3.3.5 Data Cube Modeling and Results ................ 3.4 The CO Distribution in NGC 3044 ................... 3.4.1 CO Spectra ........... ................. 3.4.2 Position-Velocity Diagram .................... 3.4.3 Integrated Intensity ........................ 3.4.4 CO Line Ratios .......................... 3.4.5 The Molecular Gas Mass ..................... 3.5 The Radio Continuum Emission in NGC 3044 ............. 3.6 The Far Infrared Ernission in NGC 3044 ................ 3.7 The Ha Emission in NGC 3044 ....................
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