University of Massachusetts Amherst ScholarWorks@UMass Amherst Doctoral Dissertations 1896 - February 2014 1-1-1987 Molecular gas in Virgo Cluster spiral galaxies. Jeffrey D. Kenney University of Massachusetts Amherst Follow this and additional works at: https://scholarworks.umass.edu/dissertations_1 Recommended Citation Kenney, Jeffrey D., "Molecular gas in Virgo Cluster spiral galaxies." (1987). Doctoral Dissertations 1896 - February 2014. 1756. https://scholarworks.umass.edu/dissertations_1/1756 This Open Access Dissertation is brought to you for free and open access by ScholarWorks@UMass Amherst. It has been accepted for inclusion in Doctoral Dissertations 1896 - February 2014 by an authorized administrator of ScholarWorks@UMass Amherst. For more information, please contact [email protected]. MOLECULAR GAS IN VIRGO CLUSTER SPIRAL GALAXIES A Dissertation Presented by Jeffrey D. Kenney Submitted to the Graduate School of the University of Massachusetts in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY May 1987 Department of Physics and Astronomy Copyright ® 1987 by Jeffrey D. Kenney All rights reserved ii Molecular Gas in Virgo Cluster Spiral Galaxies A. Dissertation Presented by Jeffrey D. Kenney Approved as to style and content by; Ji^dith S. Young, Ciiairpe^son William A. Dent, Member . Peter Schloerb, Member Stevan7^ E. Strom, Member Robert V. Krotkov, Outside Member Martha P. Hay ne^, Outs ide Member Robert Hal lock, Department Head Department of Physics and Astronomy 111 ACKNOWLEDGEMENTS First and foremost, I'd like to thank Judy Young, who suggested this project (really), and then made me do it (not really). Judy served as advisor extraordinaire and friend. Her willingness to discuss matters, her prompt feedback, and her continual encouragement made writing this thesis almost a pleasure, Steve Strom, Bill Dent, Martha Haynes, Pete Schloerb, and Bob Krotkov all served on my committee, all read the entire 930 page thesis (or so it rmst have seemed), and all provided valuable input, Steve has taught me a lot about galaxies and science. His uncontained enthu- siasm when presented with some surprising fact exemplifies what science should be. It was Bill who gave me a start in radio astronorny and tutored me in the ancient art of data calibration. Bill has given me advice on a variety of subjects during the six years I have known him, for which I am grateful. Martha deserves thanks for her correspondence and visits to Amherst. Her careful work on the HI properties of galaxies has been a source of inspiration. I appreciate Pete's insightful feedback which helped to strengthen several flimsy areas of the tome which follows. helped me write Matty others in the UMass Astronomy department have of a this thesis, although they may not have known it. Discussions Ron Snell. stimulating nature were had with Steve Lord, John Kwan, and well as Linda Tacconi, Lowell Garman, Mark Claussen, Steve Lord, as observe Virgo galaxies both of the Tacconi-Garmans were kind enough to iv for me when I was out of town on inportant business, sick with exotic tropical diseases, or just wanted to play Softball. Dave Taylor and Shuding Xie are to be thanked for their work on the calibration of Quabbin and IRAS data. Particular thanks go to Sally Rule, Jackie Golonka, and Denise Kuzmeskus for their continual help in accomplishing an infinite number of necessary tasks. Their pleasant demeanor made daily visits to the GRC bearable. I am indebted to the FCRAO Scheduling Committees, whose generous allotments of telescope time enabled this project to be completed. Several individuals outside of Amherst are to be acknowledged. Rein Warmels, Jacqueline van Gorkom and Chris Kotanyi supplied HI data prior to publication. John Stauffer provided helpful criticism of a paper describing some preliminary results of this thesis, Rob Kennlcutt did the same, and took the time to explain some essential facts about Hot emission from galaxies. Conversations with Greg Bothun clarified a couple of pertinent Issues. The Boston Red Sox of 1986 kept ny adrenaline flowing at unprecedented levels during a critical period of this work. It is hard to believe that peq)le can actually be paid to do astro- nomy. FCRAO supported me with a stipend and travel money for most of "the thesis years". Judy (remember Judy?) stepped in with financial support during a time in which I would otherwise have been left home- less and starving. I owe even more to ny parents, Phil and Ellie, who have been paying for ma to become an astronomer for nearly 3 decades. long My time as a graduate student will be fondly remembered for as v as my memory lasts. Amherst has been a great place to live, largely because of the people I've come to know and enjoy. Friendships within the department have made the last six years a rich experience. I can only hope to find myself in another place where the people are as amiable and lively as you folks. And then there's Jo, who suggested this project (not really) and has been so encouraging and supportive that it's hard to believe (really). Not only has Jo generally made life a pleasure for me, but she has spent several hundred hours typing (even this acknowledgement), making figures, and preparing the text (which she couldn't understand). Her love has provided the emotional sustenance necessary to complete this undertaking. vi ABSTRACT Molecular Gas in Virgo Cluster Spiral Galaxies (May 1987) Jeffrey D. Kenney B.S. Bates College Ph.D. University of Massachusetts Directed by: Judith S. Young We have obtained C0(J=1-K)) observations with 45" resolution at over 200 positions along the major axes of 42 Virgo cluster spiral galaxies, using the FCRAO 14-meter telescope. Although there is a general corre- lation between the CO flux of a galaxy and its optical diameter, the S^o/'^opt'^ ratio is found to depend on both the morphological type and the HI content. Analyses indicate that for the Sa-Sb and highest lumi- nosity Sc Virgo galaxies, the molecular gas contents and distributions have not been strongly affected by the cluster environment. There is a population of Hl-rich, lower-luminosity (10.9<Bt°<12.0) Sc galaxies in the outer cluster with a mean Sco/^opt'^ ratio a factor of 5 less than the other Sc's. While it also may be that the conver- sion of HI into H2 is enhanced in low mass galaxies by an interaction with the tntracluster medium, these results strongly suggest that the These attainment of an H2-dominated ISM is a function of galaxy mass. vil outer cluster low mass Virgo Sc galaxies have large massive star for- mation rates and high central HI surface densities, indicating that atomic gas plays a direct role in star formation in these systems. Galaxies which are Hl-def icient by a factor of 10 are gas -deficient (HI+H2) by only a factor of 2-3, due to the survival of large quan- tities of molecular gas. The massive-star formation rates, as indi- cated by Ha, radio continuum and far-infrared emission, are also lower by factors of ~2-3 in galaxies which are Hl-deficient by a factor of 10. Gonparison of the radial distributions of HI and H2 indicate that the total gas deficiency is manifested largely by a lack of HI in the outer galaxy. The inner disk regions, although Hl-def icient, are not significantly gas-deficient since the ISM in the inner regions of most of the galaxies in this sample are H2-clominated. The large H2/HI ratios in the inner regions of Virgo spirals indicate that either the lifetime of the molecular phase or the lifetime of GMC complexes is ~2xlO^ years in H2~dominated environments. GO emission has been detected in the center of 2 small-bulge so-so/a Virgo galaxies which remain undetected in HI. These galaxies exhibit the expected aftereffects of a severe stripping event which occurred ~2xl0^ years ago, and may be the first known examples of stripped spirals in the process of turning into SO-like systems. viii TABLE OF CONTENTS ACKNOWLEDGEMENTS ABSTRACT vH L 1ST OF TABLES *.!*.!*.*.!!*.*.!*.'.!*.*.*.!'.*.*. xi i LIST OF FIGURES *.*.!*.!!*.*.!*.*.*.*.!!!!*.!!*. xlii Chapter I. INTRODUCTION 1 1. Introduction to the Introduction 1 2. Evolution of Galaxies Within Clusters 2 3. CO as a Function of Type and Mass and the Role of Molecular Gas In Star Formation 5 4. Summary of Chapters 8 II. CO OBSERVATIONS & THE VIRGO SAMPLE 1. The Telescope System 11 2. Observational Methods 12 3. Pointing 15 4. The Virgo Sample 17 5. Foreground and Background Galaxies & the Structure of the Virgo Cluster 22 III. CO DATA & DERIVED PROPERTIES 1. Introduction 35 2. Summary of CO Data 36 3. Derivation of Global CO Fluxes 79 4. A Comparison of FCRAO and Bell Labs Virgo CO Surveys 92 5. CO Diameters 98 6. CO Asymmetries 104 IV. THE RELATION BETWEEN CO EMISSION AND MOLECULAR GAS MASS 1. Introduction Ill 2. A Virial Theorem Analysis 114 3. The Relation Between CO Intensity and Molecular Gas Surface Density 116 4. The Relation Between CO Flux and Molecular Gas Mass 120 5. Possible Variations In the CO-H2 Proportionality Factor ^22 Ix V. MOLECULAR AND ATOMIC GAS PROPERTIES OF VIRGO SPIRALS 1. Introduction 129 2. Optical and HI Data Used in Analysis 130 3. Comparison of CO Luminosities with Galaxian Mass and Optical Properties 143 4. Comparison of Global CO & HI Fluxes 161 4.1 Introduction 161 4.2 Theoretical Gas Evolution Tracks 163 4.3 Discussion 173 5. Conparison of CO, HI, and Optical Diameters 176 6. Conparison of CO and HI Radial Distributions 183 7.