Dust Within the Central Regions of Seyfert Galaxies

Georgia State University ScholarWorks @ Georgia State University Physics and Astronomy Dissertations Department of Physics and Astronomy 8-6-2007 Dust within the Central Regions of Seyfert Galaxies Rajesh Deo Follow this and additional works at: https://scholarworks.gsu.edu/phy_astr_diss Part of the Astrophysics and Astronomy Commons, and the Physics Commons Recommended Citation Deo, Rajesh, "Dust within the Central Regions of Seyfert Galaxies." Dissertation, Georgia State University, 2007. https://scholarworks.gsu.edu/phy_astr_diss/18 This Dissertation is brought to you for free and open access by the Department of Physics and Astronomy at ScholarWorks @ Georgia State University. It has been accepted for inclusion in Physics and Astronomy Dissertations by an authorized administrator of ScholarWorks @ Georgia State University. For more information, please contact [email protected]. Dust Within the Central Regions of Seyfert Galaxies by Rajesh Deo Under the Direction of D. Michael Crenshaw ABSTRACT We present a detailed study of mid-infrared spectroscopy and optical imaging of Seyfert galaxies with the goal of understanding the properties of astronomical dust around the central supermassive black hole and the accretion disk. Specifically, we have studied Spitzer Space Telescope mid-infrared spectra of 12 Seyfert 1.8-1.9s and 58 Seyfert 1s and 2s available in the Spitzer public archive, and the nuclear dust morphology in the central 500 pc of 91 narrow and broad-line Seyfert 1s using optical images from the Hubble Space Tele- scope. We have also developed visualization software to aid the understanding of the geometry of the central engine. Based on these studies, we conclude that the nuclear regions of Seyfert galaxies are fueled by dusty spirals driven by the large-scale stellar bars in the host galaxy. The accumulation of dusty gas in the central kiloparsec leads to enhanced star formation. In this case, the circumnuclear starburst and the central engine compete for dominance in the heating of the circumnuclear dust. Emission from the heated dust is most clearly seen in the mid-infrared. We find that the spectra of Seyfert 2s show the most variety in the continuum shapes due to different starburst contri- butions. We find that the spectra of Seyfert 2s that are devoid of starburst contribution are dominated by a single thermal component at a temperature of T ∼ 170 K. We also find that the mid-IR continua of Seyfert 1.8/1.9 galaxies are more like those of starburst-dominated Seyfert 2s than Seyfert 1s, contrary to expectations. We discuss the implications of these findings in the context of the Unified Model of AGN and the secular evolution of Seyfert nuclei. Index Words: astronomy, galaxies, spectroscopy, infrared, mid-infrared, dust, active galaxies, Seyfert galaxies, torus, nuclear spirals, narrow-line region, Spitzer Space Telescope, Hubble Space Telescope. Dust Within the Central Regions of Seyfert Galaxies by Rajesh Deo A DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in the College of Arts and Sciences Georgia State University 2007 Copyright Rajesh Deo 2007 Dust Within the Central Regions of Seyfert Galaxies by Rajesh Deo Major Professor: Prof. D. Michael Crenshaw Committee: Prof. Douglas R. Gies Prof. Steven B. Kraemer Prof. H. Richard Miller Prof. William H. Nelson Prof. Paul J. Wiita Electronic version approved: Office of Graduate Studies College of Arts & Sciences Georgia State University July, 2007 iv I would like to dedicate this dissertation to the memory of my father, and to my mother who has struggled against all odds in her life, so that I can comprehend this world. Acknowledgments This dissertation has benefited from a number of people at the Department of Physics and Astronomy at Georgia State University (GSU). First and foremost of all, I would like to thank my dissertation adviser, Prof. D. Michael Crenshaw for accepting me to work with him, bearing my shortcomings, teaching me important lessons and believing in me in the time of my need. I sincerely admire his ability to be critical without being overbearing, to believe in simple common-sense explanation first before invoking more complicated approaches and to strip a problem down to its bare essentials. I hope I can reproduce such simplicity in my future work. I would like to greatly thank Prof. S. B. Kraemer; he generously provided us with his Spitzer data on Seyfert 1.8/1.9s and without his good criticism of my research, there would not have been the important results that I present in this dissertation. I sincerely thank all the astronomy faculty at GSU who have instructed me. I would particularly like to thank Prof. Douglas Gies, who helped by contacting Prof. Ron Buta at the University of Alabama in regard to my questions about Hubble classification of galaxies. I would like to thank Prof. Buta for providing us access to the “De Vaucouleur’s Atlas of Galaxies” in its electronic form, as the Georgia State Library does not have a copy of the Third Revised Catalog of Galaxies. Prof. Hal McAlister kindly sent me for the Michelson Summer School during the summer of 2003 where I was introduced to the new field of optical interferometry, and I am very thankful to him for that. Prof. Paul Wiita has been a source of encouragement v vi to a generation of graduate students of Indian origin, and his expertise in astrophysics was the main reason I chose to come to GSU over other schools; he has been helpful in many ways since then. I would like to thank Prof. Bill Bagnuolo, for the occasional discussions about image processing algorithms and Fourier transforms. I would also like to thank our department chair, Prof. H. Richard Miller, for decreasing my lab teaching duties while I took care of the departmental cluster of Linux machines. I am greatly indebted to him, as he personally helped me in finding accommodation when I first came to Atlanta from India. I am also very grateful to Prof. Todd Henry for his excellent planetary system class. I would like to thank the previous senior graduate students and system managers, John McFarland and Dave Berger. I would like to thank John McFarland in particular for the large number of scripts and utility tools he wrote to manage the network of Linux machines. These tools were of great help when the task of maintaining systems was given to me. I would also like to thank our department systems administrator, Duke Windsor, for letting me maintain the Astronomy cluster of Linux machines and pursuing our requests for new hardware as quickly as possible when needed. Foremost of all, I would like to thank the entire Astronomy community at GSU for bearing with my approach to systems administration. A number of fellow graduate students have helped me in my tasks at GSU. In particular, collaborations with Alvin Das, Jay Dunn and Nick Collins at CUA have resulted in authorship on four papers and I am grateful to them. I would like to thank former graduate student Ginny McSwain for her guidance during graduate courses and matters of a career in Astronomy. I would like to thank Weichun Jao and Alvin Das for giving me a copy of their dissertation templates. I would like to thank Deepak Raghavan for the occasional discussions on the finer points of programming in IDL. Finally, I would like to thank all the rest of the graduate students, past and present, for making my experience an enjoyable one at GSU. Contents Abstract Acknowledgments v List of Tables xi List of Figures xiv Abbreviations xv 1 Introduction to Active Galaxies 1 1.1 ActiveGalaxies .......................... 2 1.1.1 Anatomy of an Active Nucleus . 3 1.1.2 Taxonomy of AGN . 6 1.1.3 AGNs studied in this dissertation . 13 1.1.4 TheUnifiedModelofAGN . 18 1.1.5 Astronomical dust and its properties . 25 1.2 Overview of this dissertation . 32 1.2.1 Geometrical modeling of NLR orientation . 32 1.2.2 HST Imaging of Nuclear Spirals in NLS1s . 34 1.2.3 Spitzer Spectroscopy of Seyfert 1.8-1.9s . 37 2 Geometry of the Narrow-Line Region 39 2.1 PreviousStudies ......................... 40 vii viii 2.2 TheDesignoftheProgram . 43 2.3 ApplicationsoftheProgram . 47 3 HST Imaging of Nuclear Spirals in NLS1s 52 3.1 Secondary bars and nuclear spirals . 52 3.1.1 Secondary/Nuclear bars . 54 3.1.2 NuclearSpirals ...................... 56 3.2 Narrow-line Seyfert 1s and AGN fueling . 58 3.3 SampleSelection ......................... 61 3.4 Image Analysis and Classification . 69 3.4.1 Nuclear Morphology Classification . 71 3.5 Results............................... 73 3.6 Implications ............................ 78 3.7 Summary ............................. 81 4 Mid-IR Spectroscopy of Seyfert Galaxies 94 4.1 EarlyInfraredStudies . 94 4.2 TheInfraredContinuum . 96 4.3 ISOSpectroscopy ......................... 98 4.3.1 IRContinua........................ 99 4.3.2 SpectralFeatures . .101 4.3.3 PAHFeatures .......................101 4.3.4 FineStructureLines . .103 4.3.5 Silicate Features . 104 4.3.6 Molecular Features . 104 4.4 Ionization/Obscuration in the Mid-IR . 105 4.5 Diagnostic Diagrams in the Mid-IR . 107 5 Spitzer/IRS Instrument and Data Analysis 111 5.1 Spitzer Space Telescope . 111 5.2 IRS Instrument Characteristics . 113 ix 5.3 Notes on IRS Data Reductions . 115 5.4 Datareductionprocess . .117 6 Mid-IR Spectra of Seyfert 1.8/1.9s 119 6.1 Spectra of Seyfert 1.8/1.9s . 124 6.2 Spectra of Type 1 and Type 2 Seyferts . 124 7 Spectral Diagnostics from Mid-IR Spectra 141 7.1 Spitzer Studies of Seyfert Galaxies . 141 7.2 Measurements and Data Tables . 144 7.3 Diagnostics with Spitzer/IRS . 154 7.4 Implications ............................158 8 Conclusions 167 8.1 OrientationGeometryoftheNLR .

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