Linking the Power Sources of Emission-Line Galaxy Nuclei from the Highest to the Lowest Redshifts A dissertation presented to the faculty of the College of Arts and Sciences of Ohio University In partial fulfillment of the requirements for the degree Doctor of Philosophy Anca Constantin August 2004 c 2004 Anca Constantin All Rights Reserved This dissertation entitled Linking the Power Sources of Emission-Line Galaxy Nuclei from the Highest to the Lowest Redshifts BY ANCA CONSTANTIN has been approved for the Department of Physics and Astronomy and the College of Arts and Sciences by Joseph C. Shields Associate Professor of Physics and Astronomy Leslie A. Flemming Dean, College of Arts and Sciences CONSTANTIN, ANCA. Ph.D. August 2004. Physics Linking the Power Sources of Emission-Line Galaxy Nuclei from the Highest to the Lowest Redshifts (185pp.) Director of Dissertation: Joseph C. Shields This dissertation searches for common grounds for the diversity of properties ex- hibited by the emission-line nuclei of galaxies, from large look-back times to the local universe. I present results of (1) a program of high signal-to-noise spectroscopy for > 44 z ∼ 4 quasars using the MMT and Keck observatories; (2) a detailed analysis of the ultraviolet and optical spectral behavior of 22 Narrow Line Seyfert 1 (NLS1) galaxies based on archival Hubble Space Telescope (HST) spectra; (3) an in-depth > investigation of the proposed link between NLS1s and z ∼ 4 quasars, by means of comparison of composite spectra, and a Principal Component Analysis; (4) a sim- ulation of Seyferts/quasars designed to explore the role of dust in modifying their observed spectral energy distribution; and (5) a sensitive search for accretion signa- tures in a large sample of nearby emission-line galaxy nuclei, employing a quantitative comparison of the nebular line flux ratios in small (HST) and large (ground-based) apertures. The low and high redshift quasars are found very similar in their emission char- acteristics, although differences exist. In particular, the data bolster indications of > supersolar metallicities in the luminous, z ∼ 4 sources, which support scenarios that assume substantial star formation concurrent or preceding the quasar phenomena. Because high-z sources are more metal enriched and more spectroscopically hetero- geneous than the NLS1s, a close connection between these objects remains doubtful. The results show that NLS1s have redder UV-blue continua than those measured in other quasars and Seyferts. The sources with UV line absorption are in general less powerful and show redder spectra, indicating that a luminosity-dependent dust absorption may be important in modifying their continua. A receding-torus –like ge- ometry seems to explain these trends and other observed correlations between quasar luminosity and continuum slope. Finally, in most of the nearby emission-line nuclei, the expected increased AGN-like behavior at smaller scales is not seen, although the nuclear emission is resolved. This suggests that these sources are not necessarily powered by accretion onto a compact object, and that the composite model proposed for the LINER/H II transition nuclei (that assumes a central accreting-type nucleus surrounded by star-forming regions) is not generally supported. Approved Joseph Shields Associate Professor of Physics and Astronomy To my parents, Ludmila and Timis Pana Acknowledgments Finishing up this work and writing it down took a lot of teaching, learning, and... a little playing. I am the one who learned, mostly. There are, however, quite a few people that made this process not only possible, but also smooth, engaging and gratifying, and I want to thank them, especially for putting up with me for all these years. My greatest salutation goes to my advisor, Joe Shields, for giving me the oppor- tunity to work on such interesting projects, and for all his support, sage counsel and patience. Most of all, I am hopeful that I learned to be at least half as patient and tactful as he was with me. Joe, you rank 1st in my role model teacher list. (I’ll let you know of any change, albeit very unlikely. In the meantime, I count on your advice.) Special thanks go to my dissertation committee members, especially for their thoughtful reading of my work, and extend to all physics and astronomy faculty at Ohio University, who, through their catching enthusiasm and genuine comity, have been constant sources of encouragement. Would I be so lucky as to plunge in similarly friendly environments in my future jobs? I really hope so, but I’ve heard it is hard to find such places... Speaking of places, and people: Don Roth, you are above words of appreciation for being there when I needed you. “Herschel” was good to me, however, much better after you “talked” to “him” first, especially about IRAF and its accompanying bugs. Of course, many warm thanks are for my fellow astro and physics colleagues, from whom I benefited invaluable intellectual stimulation, technical assistance, and of course comfort that comes from true friendship. Robert, we have spent three years of enchanting “office mate-ism.” Gabi and Andi, you had great influence (mostly good) on me, starting with choosing Ohio University as grad school, and with your help and hospitality that I so much needed in my first year in Athens, that will never be forgotten. Flori, God sent you in my way to show me what good souls are like. Bassem, you believed in me and showed me how “simple” things (particularly the codes) are. Steven, your “on deck” presence for everybody is highly appreciated. I felt honored to be trusted with your drafts. Yurii, you are so unique, I’m looking forward to seeing you again. Mangala, it has been so easy to talk to you. David and Laura, I didn’t hear you much, but your silent presence remained sensed. Keep up the good work and try to let others know about it. Swati, Manasvita, Justin, Zack, and the whole astrogroup, you have been such an enjoyable team; the wonderful greetings (with the flowers) sent to me on that January 5th meant a huge deal. May your life in the LAIR be full of adventure. Suhita and Aparna, there was always too little time spent with you, especially lately. You made India come to me. My WIPHA allies, to which I gladly add Ruth, Heather, Ennice, Karen, and Tracy, your patronage, care, and generosity overwhelmed me. The many others, whose names I will forgo mentioning here, you collectively filled up my years in Athens with zing. Cristoi, I owe you my greatest debt, for everything we’ve been (and will be) through together. Your passion for life continuously inspires me. Above all, thanks Mia for choosing us, and for appearing at the right moment, with the right smile. I know you would answer with all the candor of your heart: “moecome.” My first two years of graduate education were supported through a teaching assis- tantship appointment from Ohio University. Support for my fifth year was provided through the John Cady Graduate Fellowship. For the rest of the time spent in grad school, I benefited from financial assistance from Prof. Shields (and Prof. Statler, for one summer, if I recall correctly) through external grants. The Ohio University Graduate Student Senate is acknowledged for partial funding awarded to attend the 203rd Meeting of the American Astronomical Society, held in January, 2004, in At- lanta, Georgia. The financial burden of many other meetings, summer schools and workshops was generously supported by Prof. Shields through his grants. Contents Abstract 4 Acknowledgements 7 List of Figures 11 List of Tables 17 1 Introduction 18 1.1 Rationale ................................. 18 1.2 ActiveGalacticNuclei .......................... 19 1.2.1 The Nucleus Types and their Oddities . 20 1.2.2 The Central Power Source of Low Luminosity Nuclei . 22 1.3 LimitationsofPreviousWork . 24 1.4 Thiswork ................................. 26 2 Emission-Line Properties of z > 4 Quasars 27 2.1 Introduction................................ 27 2.2 Observations&dataanalysis . 28 2.3 Spectroscopicproperties . 39 2.3.1 Generalcharacteristics . 39 2.3.2 OIandNV............................ 45 2.3.3 The EW vs. Luminosity correlation . 47 2.3.4 Selectionbiases .......................... 51 2.4 Discussion................................. 54 2.5 Conclusions ................................ 57 3 Ultraviolet and optical properties of Narrow-Line Seyfert 1 galaxies 59 3.1 Introduction................................ 59 3.2 The NLS1 sample & data processing . 61 3.3 TheNLS1compositespectra. 68 3.3.1 Overallcontinuum ........................ 69 9 10 3.3.2 ReddeningandAbsorption. 72 3.3.3 TheUVspectrum......................... 75 3.3.4 Theopticalcomposite . 75 3.3.5 EmissionLines .......................... 77 3.4 Are NLS1s the analogues of high z QSOs? ............... 88 3.4.1 Direct comparison of composite spectra . 90 3.4.2 Principal Component Analysis . 93 3.5 Conclusions ................................ 97 4 Dust Reddening and the AGN Spectral Energy Distribution 99 4.1 Introduction................................ 99 4.2 Themodel:recedingtorus . 103 4.2.1 Simulationparameters . 104 4.3 Results................................... 110 4.3.1 Anoteofcaution ......................... 118 4.3.2 The fraction of obscured accretion power . 119 4.4 Summary&Conclusions . 120 5 The Power Sources of the Low Luminosity Emission-Line Galaxy Nuclei 122 5.1 Introduction................................ 122 5.2 The nuclei sample & data processing . 125 5.2.1 Thedata.............................. 125 5.2.2 Measurements of emission-lines . 131 5.2.3 New evidence for broad emission . 139 5.2.4 General nuclear properties of the sample . 144 5.3 Is the nuclear emission resolved? . 149 5.4 The nebular excitation and the central engines . ..... 152 5.5 Discussion ................................. 158 5.5.1 TheremarkablenucleusofNGC4736 . 161 5.6 Summary&Conclusions . 164 6 Summary 167 6.1 BasicResults ............................... 167 6.1.1 Nuclear activity at the highest redshifts . ... 167 6.1.2 Getting closer to home: the NLS1 galaxies .