A Search for the Smallest Supermassive Black Holes Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Himel Ghosh, M.A. Graduate Program in Astronomy The Ohio State University 2009 Dissertation Committee: Professor Smita Mathur, Advisor Professor Paul Martini Professor Andrew P. Gould Copyright by Himel Ghosh 2009 ABSTRACT Relations between supermassive black holes (SMBHs) and their host galaxies are now well known, but several questions remain: Do all galaxies harbor SMBHs? Do correlations between BH mass and host galaxy properties extend to lower mass BHs and all galaxy types? Is the galactic bulge or the dark matter halo the defining component for the nuclear BH? Answering these questions requires a study of low mass SMBHs, in particular those that reside in the latest-type spiral galaxies. While the presence of an active galactic nucleus (AGN) provides certain proof of the existence of an SMBH, galaxies that are not previously known to host AGNs may nevertheless have SMBHs at their centers. In other words, a galaxy may appear quiescent when in reality there is an accreting SMBH, if the accretion level is low enough. This thesis presents a search for such SMBHs by looking for the presence of low-level nuclear activity, as evidenced primarily by their x-ray emission, in a well-defined sample of nearby, optically quiescent spiral galaxies. This work demonstrates that traditional methods of identifying AGNs, developed over the course of studying luminous (> 1042 erg s−1) AGNs, are inadequate for ∼ the population of low luminosity AGNs found in nearby galaxies, and develops the ii techniques that must be used instead. These techniques are then applied to an x-ray survey of nearby, face-on spiral galaxies. The survey includes new snapshot observations of 37 galaxies, which are combined with archival data for a further 18 galaxies. Where available, multi-wavelength data are used to help distinguish AGNs from other types of x-ray sources. These observations show the power of x-ray observations in detecting hidden AGNs, and also address the question of the prevalence of SMBHs in spiral galaxies that do not have bulges. This study has uncovered 14 previously unknown AGNs and strong AGN candidates, including two in galaxies of type Sd and Sdm. If the latter are confirmed as bona fide AGNs they will be only the fourth and fifth AGNs known to exist in bulgeless galaxies. iii ACKNOWLEDGMENTS I wish to thank my advisor, Prof. Smita Mathur, for her superb mentoring. She has been at all times supportive and encouraging, always optimistic but realistic, always solicitous but never condescending. It has been a pleasure to work with her, and I have learned much from her both as a scientist and as a person. I am grateful to my family for their moral support during this endeavor, and especially to my wife Pampa for her support, very practical help, and unvarnished advice, all of which were invaluable. Finally I would like to thank the faculty, staff, and other graduate students in the Department of Astronomy for making possible an exciting and enjoyable sojourn that now comes to an end. iv VITA 1996 ........................... A.B. cum laude Physics, Amherst College 1998 ........................... M.A. Astronomy, Columbia University 1998 – 2001 . Computer Specialist, Smithsonian Astrophysical Observatory 2001 – 2003 . Research Astrophysicist, Smithsonian Astrophysical Observatory 2003 – present . Graduate Teaching and Research Associate, The Ohio State University PUBLICATIONS Research Publications 1. J. Kuraszkiewicz, B. J. Wilkes, G. Schmidt, H. Ghosh, P. Smith, R. Cutri, D. Hines, E. M. Huff, J. C. McDowell, and B. Nelson, “The Spectral Energy Distributions of Red 2MASS AGN”, ApJ, 629, 1143, (2009). 2. H. Ghosh, S. Mathur, F. Fiore, and L. Ferrarese, “Low-level Nuclear Ac- tivity in Nearby Spiral Galaxies”, ApJ, 687, 216, (2008). 3. H. Ghosh, R. W. Pogge, S. Mathur, P. Martini, and J. C. Shields, “Chandra Observations of Candidate ‘True’ Seyfert 2 Nuclei”, ApJ, 656, 105, (2007). 4. M. C. Bentz, K. D. Denney, E. M. Cackett, M. Dietrich, J. K. J. Fogel, H. Ghosh, K. D. Horne, C. Kuehn, T. Minezaki, C. A. Onken, B. M. Peterson, R. W. Pogge, V. I. Pronik, D. O. Richstone, S. G. Sergeev, M. Vestergaard, M. G. Walker, and Y. Yoshii, “NGC 5548 in a Low-Luminosity State: Implications for the v Broad-Line Region”, ApJ, 662, 205, (2007). 5. K. D. Denney, M. C. Bentz, B. M. Peterson, R. W. Pogge, E. M. Cack- ett, M. Dietrich, J. K. J. Fogel, H. Ghosh, K. D. Horne, C. Kuehn, T. Minezaki, C. A. Onken, V. I. Pronik, D. O. Richstone, S. G. Sergeev, M. Vestergaard, M. G. Walker, and Y. Yoshii, “The Mass of the Black Hole in the Seyfert 1 Galaxy NGC 4593 from Reverberation Mapping”, ApJ, 653, 152, (2006). 6. M. C. Bentz, K. D. Denney, E. M. Cackett, M. Dietrich, J. K. J. Fogel, H. Ghosh, K. Horne, C. Kuehn, T. Minezaki, C. A. Onken, B. M. Peterson, R. W. Pogge, V. I. Pronik, D. O. Richstone, S. G. Sergeev, M. Vestergaard, M. G. Walker, and Y. Yoshii, “Reverberation-based Mass for the Central Black Hole in NGC 4151”, ApJ, 651, 775, (2006). 7. B. J. Wilkes, K. A. Pounds, G. D. Schmidt, P. S. Smith, R. M. Cutri, H. Ghosh, B. Nelson, and D. C. Hines, “XMM-Newton Observations of Red AGNs”, ApJ, 634, 183, (2005). 8. J. D. Silverman et al. (the ChaMP collaboration), “Hard X-Ray-emitting Active Galactic Nuclei Selected by the Chandra Multiwavelength Project”, ApJ, 618, 123, (2005). 9. H. Ghosh, D. L. DePoy, A. Gal-Yam, B. S. Gaudi, A. Gould, A., C. Han, Y. Lipkin, D. Maoz, E. O. Ofek, B.-G. Park, and 53 coauthors, “Potential Direct Single-Star Mass Measurement”, ApJ, 615, 450, (2004). 10. D.-W. Kim, et al. (the ChaMP collaboration), “Chandra Multiwave- length Project. I. First X-Ray Source Catalog”, ApJS, 150, 19, (2004). 11. D.-W. Kim, et al. (the ChaMP collaboration), “Chandra Multiwave- length Project II: First Results of X-ray Source Properties”, ApJ, 600, 59, (2004). 12. P. J. Green, et al. (the ChaMP collaboration), “The Chandra Multi- wavelength Project:Optical Followup of Serendipitous Chandra Sources”, ApJS, 150, 43, (2004). 13. S. Mathur, B. J. Wilkes, and H. Ghosh, “Chandra Detection of Highest Redshift (z 6) Quasars in X-rays”, ApJL, 570, L5, (2002). ∼ 14. B. J. Wilkes, G. D. Schmidt, R. M. Cutri, H. Ghosh, D. C. Hines, B. Nelson, and P. S. Smith, “The X-ray Properties of 2MASS Red Active Galactic Nuclei”, ApJL, 564, L65, (2002). vi FIELDS OF STUDY Major Field: Astronomy vii Table of Contents Abstract..................................... ii Acknowledgments................................ iv Vita ....................................... v ListofTables .................................. xi ListofFigures.................................. xiii Chapter 1 Introduction ............................ 1 1.1 ScopeoftheDissertation......................... 6 Chapter 2 Proof of Principle: Six Galaxies from the Chandra Archive 7 2.1 Introduction................................ 7 2.2 Sampleselection.............................. 8 2.3 Dataanalysis ............................... 9 2.4 TheGalaxies ............................... 11 2.4.1 NGC3169............................. 11 2.4.2 NGC3184............................. 13 2.4.3 NGC4102............................. 18 2.4.4 NGC4647............................. 26 2.4.5 NGC4713............................. 30 2.4.6 NGC5457(M101) ........................ 33 2.5 Discussion................................. 43 viii Chapter 3 A strong candidate AGN in NGC 4713 ........... 58 3.1 Introduction................................ 58 3.2 Observationsanddataanalysis . 59 3.3 Resultsanddiscussion .......................... 61 3.4 The UV variability of NGC 4713 . 65 Chapter 4 The Chandra Survey: I. The Archival Data ........ 70 4.1 SampleSelection ............................. 70 4.2 Dataanalysis ............................... 71 4.3 TheGalaxies ............................... 73 4.3.1 Group 1: The best AGN candidates . 74 4.3.2 Group 2: Candidates with large uncertainties . 84 4.3.3 Group 3: Nuclei with uncertain or no detection . 88 4.4 Discussion................................. 90 Chapter 5 The Chandra Survey: II. The Detected Nuclei ...... 105 5.1 Introduction................................ 105 5.2 The seven nuclear x-ray sources . 105 Chapter 6 The Chandra Survey: III. The Nondetections ....... 111 6.1 Introduction................................ 111 6.2 Stackinganalysis ............................. 112 6.3 Results................................... 114 6.4 Discussion................................. 120 Chapter 7 Conclusions and Future Directions .............. 135 ix 7.1 Futureresearch .............................. 144 Bibliography ................................... 149 x List of Tables 2.1 Targets and observation parameters . 46 2.1 Targets and observation parameters . 47 2.2 X-rayMeasurements ........................... 48 2.3 NGC5457X-rayMeasurements . 49 2.3 NGC5457X-rayMeasurements . 50 2.3 NGC5457X-rayMeasurements . 51 2.4 X-RaySpectralFits............................ 52 2.4 X-RaySpectralFits............................ 53 2.4 X-RaySpectralFits............................ 54 2.5 Inferred nuclear luminosities . 55 2.5 Inferred nuclear luminosities . 56 2.6 NGC 3184 luminosity in Spitzer bands.................. 57 3.1 Spectral model parameters and goodness of fit.. 69 4.1 Targets and observation parameters . 96 4.1 Targets and observation parameters . 97 4.1 Targets and observation parameters . 98 4.2 X-rayMeasurements