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Active Galactic Nuclei in Dwarf Galaxies

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Active Galactic Nuclei in Dwarf Galaxies Active Galactic Nuclei in Dwarf Galaxies by Vivienne Francesca Baldassare A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Astronomy and Astrophysics) in The University of Michigan 2017 Doctoral Committee: Associate Professor Elena Gallo, Chair Dr. Laura Ferrarese, Herzberg Institute for Astrophysics Associate Professor Oleg Y. Gnedin Associate Professor Dragan Huterer Associate Research Professor Monica Valluri Vivienne Francesca Baldassare [email protected] ORCID iD: 0000-0003-4703-7276 c Vivienne Francesca Baldassare 2017 “Because survival is insufficient” -Station Eleven by Emily St. John Mandel To Jeremy and Henri. ii ACKNOWLEDGEMENTS Firstly, I am incredibly grateful to my PhD advisor, Elena Gallo, for her mentorship, support, and guidance. Over the last five years, Elena has demonstrated to me how to be a careful, quantitative, and thorough scientist while never losing sight of the larger context of your results. I have benefited greatly from her advice and perspective on many matters, scientific and otherwise. I have been fortunate to be surrounded by many excellent scientists. In particular, I would like to acknowledge my collaborators Amy Reines and Jenny Greene for their mentorship and scientific guidance, which have helped shape my career in astronomy. I am grateful to the other members of my thesis committee – Laura Ferrarese, Oleg Gnedin, Monica Valluri, and Dragan Huterer – for their input throughout my graduate career; their comments and suggestions have improved this thesis and my work overall. My sincerest gratitude is extended to the entire University of Michigan Astronomy Department. It was a pleasure to earn my degree in such a collaborative, supportive, and friendly environment. I am especially grateful for my graduate cohort, who made study sessions more bearable with friendship and nachos. I am grateful for financial support in the form of a National Science Foundation Grad- uate Research Fellowship, and a Predoctoral Fellowship from the Rackham Graduate School at the University of Michigan. I am thankful to my parents, Andrea and Wayne, for their unending support, love, and encouragement, and for always reminding me to “keep fighting”. iii Thank you to my sister and co-conspirator Lily for inspiring me every day to be more bold and confident, and for being the Frodo to my Samwise. Finally, I am especially grateful to have taken this journey alongside my husband, Jeremy Hoskins: my best friend; co-adventurer; and the guardian of my solitude. iv TABLE OF CONTENTS DEDICATION :::::::::::::::::::::::::::::::::::::::::::: ii ACKNOWLEDGEMENTS ::::::::::::::::::::::::::::::::::::: iii LIST OF FIGURES ::::::::::::::::::::::::::::::::::::::::: vii LIST OF TABLES :::::::::::::::::::::::::::::::::::::::::: xiii ABSTRACT :::::::::::::::::::::::::::::::::::::::::::::: xiv CHAPTER I. Introduction ..........................................1 1.1 Background: active galactic nuclei . .1 1.1.1 Brief history of AGNs . .1 1.1.2 AGN structure . .2 1.1.3 Observational signatures of AGNs . .4 1.2 Evolution of galaxies and central massive black holes . .8 1.2.1 Scaling relations . .8 1.2.2 BH mass measurements . 10 1.3 Supermassive black hole formation . 13 1.3.1 Seed formation mechanisms . 13 1.3.2 Observational tests of BH formation theories . 16 1.4 Dwarf galaxies with AGN signatures . 17 1.5 Thesis contents . 20 II. Multi-epoch spectroscopy of dwarf galaxies with optical AGN signatures ........ 22 2.1 Motivations and Aims . 22 2.2 Introduction . 23 2.3 Observations and Data Reduction . 26 2.4 Analysis . 30 2.4.1 Emission line modeling . 30 2.4.2 Stellar velocity dispersions . 33 2.5 Broad line AGN candidates: Results . 34 2.5.1 Transient broad Hα ............................. 39 2.5.2 Persistent broad Hα ............................ 39 2.5.3 Ambiguous galaxies . 44 2.6 Type II supernovae in dwarf galaxies . 45 2.6.1 A Possible SN IIn in RGG J . 51 2.7 Discussion . 52 2.8 Conclusions . 54 2.9 Emission line fitting examples . 55 v III. A 50,000 solar mass black hole in the nucleus of a dwarf galaxy ............. 57 3.1 Motivation and Aims . 57 3.2 Introduction . 58 3.3 Observations and Data Reduction . 59 3.3.1 SDSS . 59 3.3.2 MagE . 60 3.3.3 Chandra X-ray Observatory . 61 3.3.4 Hubble Space Telescope . 61 3.4 Optical spectroscopic analysis . 62 3.4.1 Emission-line modeling . 62 3.4.2 Black hole mass . 66 3.5 X-ray analysis . 68 3.6 Imaging analysis . 68 3.6.1 SDSS Imaging . 68 3.6.2 HST imaging . 71 3.6.3 Comparison of SDSS and HST imaging analyses . 76 3.7 Scaling relations . 78 3.8 Conclusions . 82 IV. X-ray and ultraviolet properties of AGN in dwarf galaxies ................ 83 4.1 Motivation and Aims . 83 4.2 Introduction . 83 4.3 Observations and Analysis . 87 4.3.1 Chandra X-ray Observatory . 91 4.3.2 Hubble Space Telescope . 94 4.3.3 Archival data . 94 4.4 Results . 95 4.4.1 Nuclear X-ray Emission . 95 4.4.2 UV-to-X-ray flux ratios . 96 4.4.3 X-ray hardness ratio . 97 4.5 Discussion . 100 4.5.1 Origin of X-ray emission . 100 4.5.2 Comparison to more massive AGN . 102 4.6 Conclusions . 105 V. Summary and future directions ............................... 112 5.1 Summary . 112 5.2 Future directions . 114 BIBLIOGRAPHY :::::::::::::::::::::::::::::::::::::::::: 116 vi LIST OF FIGURES Figure 1.1 Simplified schematic of an active galactic nucleus (not to scale). Figure inspired by schematic from Urry & Padovani (1995). Depending on the viewing angle, the emission from the broad line region clouds may or may not be visible. .5 1.2 Typical quasar spectral energy distribution from Elvis et al. (1994). .6 1.3 Stellar orbits at the center of the Milky Way. This image was created by Prof. Andrea Ghez and her research team at UCLA and is from data sets obtained with the W. M. Keck Telescopes. 11 2.1 Red channel He-Ne-Ar arc lamp spectrum taken as part of our observations with the Dual- Imaging Spectrograph on the ARC 3.5m telescope. Note that the shape of the instrumental broadening has two components – a narrow core and a broad base. 32 2.2 [SII]λλ6716; 6731 lines from the DIS spectrum of RGG C (NSA 109990). The black line shows the observed spectrum, the red line is our best fit to the two lines, and the solid blue lines show the various components corresponding to our best fit of the two [SII] lines. We constrain the relative heights and widths of the “narrow” and “broad” components and use that model to fit the narrow-lines in the Hα-[NII] complex for DIS observations. 33 2.3 Spectral region of the MagE spectrum of RGG 119 used to measure the stellar velocity dispersion in pPXF. We use a region of the spectrum encompassing the Mg b triplet. The observed spectrum is shown in gray, while the shaded red region represents the range of outputs from pPXF for the chosen combinations of additive and multiplicative polynomials. 34 2.4 Positions of our SDSS broad Hα targets on the BPT diagram (Baldwin et al. 1981) us- ing the classification of Kewley et al. (2006). Each target is plotted in a different color. Note that there are two points for RGG J corresponding to the two SDSS observations. A diamond indicates that broad Hα was present in follow-up spectroscopy (‘persistent’), a square indicates an ambiguous follow-up broad Hα detection, and a circle indicates that broad Hα was not detected in follow-up observations (‘transient’). 35 2.5 The observed Hα-[NII] complex and corresponding best-fit profile for the SDSS, DIS, and OSMOS spectra of RGG C (NSA 109990). In each, the dark gray line represents the observed spectrum. The narrow emission line fit is plotted in green, and the blue shows the fit to broad Hα emission. The overall best-fit model is given in red, and the light gray line below the observed spectrum shows the residual between the observed spectrum and the best fit, offset by an arbitrary amount. This galaxy is classified as having transient broad Hα emission. 40 vii 2.6 The observed Hα-[NII] complex and corresponding best-fit profile for the SDSS and DIS spectra of RGG 9. The dark gray line represents the observed spectrum. The narrow emission line fit is plotted in green, and the blue shows the fit to broad Hα emission. The overall best-fit model is given in red, and the light gray line below the observed spectrum shows the residual between the observed spectrum and the best fit, offset by an arbitrary amount. We classify this galaxy as having persistent broad Hα................ 41 2.7 The observed Hα-[NII] complex and corresponding best-fit profile for the SDSS, MagE, and DIS spectra of RGG 119 (NSA 79874). In each, the dark gray line represents the observed spectrum. The narrow emission line fit is plotted in green, and the blue shows the fit to broad Hα emission. The overall best-fit model is given in red, and the light gray line below the observed spectrum shows the residual between the observed spectrum and the best fit, offset by an arbitrary amount. We classify this galaxy as having persistent broad Hα............................................... 42 2.8 Position of low-mass AGNs on the relation between black hole mass and stellar velocity dispersion. The MBH − σ? relations determined in Gultekin¨ et al. (2009), McConnell & Ma (2013), and Kormendy & Ho (2013) are plotted. We also show points for systems with dynamical BH mass measurements as compiled by Kormendy & Ho (2013) (pseudobulges are shown as gray squares, while classical bulges are plotted as gray circles). The black hole mass and stellar velocity dispersion for RGG 119 (NSA 79874; shown as a purple circle) were measured in this work.
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