Universität zu Köln

Wagner, Jan Florian (2014). RFI Mitigation for VLBI and Arrays - Water Megamasers in Active Galaxies. PhD thesis, Universität zu Köln.

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Abstract

This thesis studies the central parsec in active galaxies via spectral line observations of OH and water megamasers and millimeter-wave interferometry. The aims are four-fold: 1) measure the mass of the supermassive black hole in active galactic nuclei (AGN) through circumnuclear water maser observations, 2) measure the Hubble constant through circumnuclear water maser observations, 3) mitigate the radio frequency interference that degrades spectral line observations, and 4) probe the innermost regions of AGN by expanding a mm-wavelength interferometer. The current paradigm conjectures that AGN contain a supermassive black hole The high spatial resolution of very long baseline radio interferometry (VLBI) allows to track AGN-launched jets over pc to kilo-pc scales outside an AGN. Within AGN, water megamaser emission mapped by VLBI is an excellent tracer of the sub-pc structure, in particular of the accretion disk. Its rotation curve, traced by water masers, allows an accurate SMBH mass measurement, important for constraining the empirical relation between black hole mass and stellar velocity dispersion in the galactic bulge – current evidence suggest that this MBH–sigma -relation is not universal, indicating differences in SMBH feeding, accretion history and AGN evolution. Disk masers further yield accurate distances to nearby maser galaxies by an almost purely geometric means. This allows measuring the current rate of expansion of the Universe, described by the Hubble constant, H0, an important cosmological parameter. To constrain DE models the key goal of the Megamaser Cosmology Project (MCP; Braatz, NRAO) is to measure H0 to at least 3% precision. Relatively few (~5%) active galaxies have been detected in water masers. In this thesis I carried out a water maser survey in nearby galaxies, some with AGN, some also detected in the dissociation product of water, the neutral hydroxyl radical (OH). Four new water masers were detected, including OH-detected galaxies, such as NGC 4261 famous for its dusty torus. The MCP project by J. Braatz et al. conducts 22 GHz VLBI and single-dish observations of disk maser galaxies. I analyzed the data of three quite different maser galaxies with putative AGN (NGC 23, UGC 3193 and IC 2560). The maser data for NGC 23 suggest either an association with a possibly truncated low-luminosity jet, or exceptionally luminous nuclear /extranuclear star formation masers. The AGN disk water masers in UGC 3193 reveal a large accretion disk with two rings suggestive of a disrupted disk around a low central SMBH mass of about 0.6+-0.2 x 10^6 Msun The disk masers in IC 2560 on the other hand indicate a SMBH mass of 5.4^+0.9_-0.6 x 10^6 Msun, and undermassive in the common MBH-sigma -relation, consistent the trend seen in other water maser galaxies. The IC 2560 disk masers also allowed the Hubble constant to be measured, resulting in an H0 of 67.7^+11.6_-8:9 km/s/Mpc. Combined with recent MCP results (UGC 3789, NGC 6264) this yields a new maser-based Hubble constant of 68.4+-5.3 km/s/Mpc (8%). Spectral lines observations are often degraded by man-made radio frequency interference (RFI). Thus I also discuss two techniques for mitigating RFI. The first was implemented in a popular VLBI software correlator. I evaluate the theoretical and practical performance, also in a VLBI search for 1.6 GHz OH in tori of Cygnus A and NGC 1068. I find the mitigation method to be effective but limited in practice due to the particular software correlator architecture. The second method improves over two existing approaches for antenna arrays, including focal plane arrays. While current instrumentation did not allow an immediate application, e.g., in the maser survey, I find that the method shows great potential for future observations in presence of RFI. Lastly, our recent work on expanding a global sub-millimeter VLBI array has enabled extreme angular resolution, suffcient to resolve the SMBH/disk system and the jet launching region. I present the first 230 GHz VLBI observation of the core region of blazar 3C 279. The work allows extreme-resolution observations of, e.g., Sgr A* and the SMBHs in M87 that will lead to a better understanding of SMBH spin, accretion, and jet launching.

Item Type:	Thesis (PhD thesis)
Translated abstract:	Abstract Language Diese Arbeit untersucht die inneren Parsec (pc) aktiver Galaxien anhand Spektrallinenbeobachtungen und Radiointerferometrie. Aktive Galaxien beherbergen eines der leuchtkräftigsten Objekte des Universums, den Aktiven Galaktischen Kern (engl. AGN), eine kompakte zentrale Region die extreme Leuchtstärken erreichen kann. Die Lehrmeinung vermutet ein supermassives Schwarzes Loch (engl. SMBH) im inneren sub-pc-Bereich eines AGN, mit Materiezufluss aus einer das SMBH umgebenden rotierenden Akkretionsscheibe (AS). Man vermutet außerdem, dass das SMBH/AS-System teilweise durch einen äußeren sub-10 pc Materie-“Torus” verdeckt wird. In einigen AGN stößt die innere Region auch einen relativistischen Materiestrom aus. Die Mechanismen die diesen “Jet” bilden sind umstritten, da die Region bisher nicht direkt beobachtet und bildgebend aufgelöst werden konnte. Mit Radiointerferometrie auf langen Basislinien (engl. VLBI) kann man z.B. der Jet-Materiefluss außerhalb des AGN über mehrere (kilo-)pc verfolgen. Die innere sub-pc -Region kann wiederum durch VLBI-Beobachtungen leuchtstarker Wassermaser (H2O-Emissionslinien) erfasst werden. Wassermaser werden oft in Jet-Nähe, aber auch in der sub-pc AS beobachtet. Die durch “Disk-Maser” abgetastete Rotationskurve der AS erlaubt eine genaue Bestimmung der Masse des zentralen SMBH. Dies liefert wichtige Daten zur empirischen Relation zwischen der SMBH-Masse und der stellaren Geschwindigkeitsdispersion im Zentralbereich der Galaxie (MBH-sigma -Relation). Sie scheint bekanntermaßen nicht universell zu sein. Dies deutet auf Unterschiede in der AGN- und SMBH-Evolution in verschiedenen Galaxientypen hin. Disk-Maser ermöglichen auch eine präzise und nahezu rein geometrische Entfernungsmessung zu Masergalaxien. Anhand der Distanz lässt sich die Expansionsrate des Universums bestimmen, also die Hubble-Konstante, H0, einem wichtigen kosmologischen Parameter. Anders als bei populären Methoden hängt die maserbasierte H0-Messung nicht von teils noch umstrittenen Details der Astrophysik ab. Mit einem exakten Wert für H0 lassen sich konkurrierende Dark Energy (DE) -ähnliche Modelle der theoretischen Physik ausschließen. Deshalb ist das Hauptziel des Megamaser Cosmology Project, für das ich drei recht verschiedene Masergalaxien analysiert haben, die Bestimmung von H0 auf eine Genauigkeit von mindestens 3%. Noch sind relativ wenige Masergalaxien bekannt. In dieser Arbeit habe ich eine Masersuche in aktiven Galaxien, und Galaxien mit Hydroxyl-Radikal (OH) -Spektrallinien (einem Dissoziationsprodukt von Wasser) durchgeführt. Vier neue Detektionen enthielten u.a. einen Disk-Maser, und einen Jet-Maser in der Galaxie NGC 4261, bekannt für ihren Torus. Unter dem MCP-Projekt von J. Braatz et al. habe ich drei recht verschiedene Masergalaxien mit möglichen AGN niedriger Leuchtstärke (NGC 23, UGC 3193 und IC 2560) analysiert. Die Maser in NGC 23 sind entweder mit einem gekürzten Jet von sehr niedriger Leuchtkraft assoziert, oder sind ungewöhnlich leuchtstarke Maser in inneren Sternformationregionen in NGC 23. Die Disk-Maser in UGC 3193 andererseits beschreiben eine weite, gewölbte und unterbrochene AS mit zwei Ringen, die eine SMBH-Masse von nur 0.6+-0.2 x 10^6 Msun umgeben. Die Disk-Maser in IC 2560 deuten wiederum auf eine SMBH-Masse von 5.4^+0.9_-0.6 x 10^6 Msun, untermassiv im Vergleich zu der MBH–sigma -Relation. Dieser Trend ist auch in anderen Masergalaxien sichtbar. Zusätzlich erlaubten die Disk-Maser in IC 2560 eine Messung der Hubble-Konstante von 67.7^+11.6_-8.9 km/s/Mpc. Mit den Resultaten des MCP aus zwei weiteren Galaxien (UGC 3789, NGC 6264) ist der maserbasierten H0-Wert 68.4+-5.3 km/s/Mpc (8%). Spektrallinienbeobachtungen leiden oft unter terrestrischen Störsignalen (engl. RFI). Diese Arbeit enthält deshalb auch zwei Methoden zur RFI-Abwehrung (engl. RFI mitigation). Die erste Methode wurde in einem bekannten VLBI-Softwarekorrelator implementiert und die theoretischen und praktischen Leistung wurde untersucht, auch in einer VLBI-Suche nach 1.6 GHz OH in den Tori von Cygnus A und NGC 1068. Die Methode an sich ist effektiv, aber wegen der Softwarearchitektur des Korrelators konnte die volle Leistungsfähigkeit nicht erreicht werden. Die zweite Methode, RFI-Subtraktion für Antennenarrays, stellt eine Verbesserung zweier Ansätze dar. Die aktuelle Antenneinstrumentation erlaubte zwar keine sofortige Anwendung der Methode, sie zeigte jedoch großes Potential für Beobachtungen mit zukünftigen Arrays und Multi-pixel-Empfängern in der Präsenz von RFI. Um zukünftig auch die innerste AGN-Region um das SMBH bildgebend aufzulösen, das Ziel der des GMVA und der Event Horizon Telescope (EHT) -Kollaboration das zu einem besseren Verständis des SMBH-Spins, Akkretion und der Jet-Entstehung führen wird, arbeiteten wir an einer Erweiterung eines globalen Sub-Millimeter-VLBI-Arrays. Im letzten Kapitel werden die Ergebnisse einer ersten extrem hochauflösenden Testbeobachtung von 3C 279 vorgestellt. German
Creators:	Creators Email ORCID ORCID Put Code Wagner, Jan Florian jan.wagner@iki.fi UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-56332
Date:	26 June 2014
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Physics > Institute of Physics I
Subjects:	Physics
Uncontrolled Keywords:	Keywords Language radio astronomy UNSPECIFIED active galaxies UNSPECIFIED
Date of oral exam:	26 June 2014
Referee:	Name Academic Title Eckart, Andreas Prof. Dr. Zensus, J. Anton Prof. Dr.
References:	G. E. Addison, et al. (2013). ‘Cosmological constraints from baryon acoustic oscillations and clustering of large-scale structure’. ArXiv e-prints . 123 G. B. Airy (1835). ‘On the Diffraction of an Object-glass with Circular Aperture’. Transactions of the Cambridge Philosophical Society 5:283. 13 W. Alef (2004). ‘A Review of VLBI Instrumentation’. In R. Bachiller, F. Colomer, J.-F. Desmurs, & P. de Vicente (eds.), European VLBI Network on New Developments in VLBI Science and Technology, pp. 237–244. 15 A. Alonso-Herrero, et al. (2009). ‘PMAS optical integral field spectroscopy of luminous infrared galaxies. I. The atlas’. A&A 506:1541–1562. 92, 101, 103 A. Alonso-Herrero, et al. (2013). ‘Local Luminous Infrared Galaxies. III. Co-evolution of Black Hole Growth and Star Formation Activity?’. ApJ 765:78. 221 A. Alonso-Herrero, et al. (2012). ‘Local Luminous Infrared Galaxies. II. Active Galactic Nucleus Activity from Spitzer/Infrared Spectrograph Spectra’. ApJ 744:2. 92, 103 N. Andreasian & D. Alloin (1994). ‘More ultraluminous IRAS galaxies as interacting systems.’. A&AS 107:23–28. 84 N. K. Andreasian (1992). ‘Rotation curves of two galaxies with megamaser radiation’. In S. S. Holt, S. G. Neff, & C. M. Urry (eds.), American Institute of Physics Conference Series, vol. 254 of American Institute of Physics Conference Series, pp. 617–620. 84, 85 R. Antonucci (1993). ‘Unified models for active galactic nuclei and quasars’. ARA&A 31:473–521. 4, 5, 6, 92 I. Aretxaga, et al. (1999). ‘Seyfert 1 Mutation of the Classical Seyfert 2 Nucleus NGC 7582’. ApJ 519:L123–L126. 6 M. K. Argo, et al. (2007). ‘OH main line masers in the M82 starburst’. MNRAS 380:596–608. 77 R. Athreya (2009). ‘A New Approach to Mitigation of Radio Frequency Interference in Interferometric Data’. ApJ 696:885–890. 31 J. M. Attridge (2001). ‘86 GHZ Very Long Baseline Polarimetry of 3C 273 and 3C 279 with the Coordinated Millimeter VLBI Array’. ApJ 553:L31–L34. 149, 163 W. A. Baan (2010). ‘Setting the stage - layers of RFI Mitigation’. In RFI 2010 – Proceedings of the RFI mitigation workshop. PoS. 24 W. A. Baan & J. A. Irwin (1995). ‘The Nuclear Structure of NGC 3079’. ApJ 446:602. 77 W. A. Baan, et al. (1982). ‘Broad hydroxyl emission in IC 4553’. ApJ 260:L49–L52. 8 U. Bach, et al. (2002). ‘Proper motion in Cygnus A’. In E. Ros, R. W. Porcas, A. P. Lobanov, & J. A. Zensus (eds.), Proceedings of the 6th EVN Symposium, p. 155. 47, 51 K. Bamba, et al. (2012). ‘Dark energy cosmology: the equivalent description via different theoretical models and cosmography tests’. Ap&SS 342:155–228. 123, 218, 220 A. Baudry & N. Brouillet (1996). ‘Spatial distribution and nature of H 2 O masers in Messier 82.’. A&A 316:188–195. 77 C. Beaudoin, et al. (2013). ‘Receiver Upgrade for the GGAO 12m VLBI system’. In N. Zubko & M. Poutanen (eds.), Proceedings of the 21st Meeting of the European VLBI Group for Geodesy and Astrometry, pp. 13–16. EVGA. 26 V. Belitsky, et al. (2007). ‘Facility heterodyne receiver for the Atacama Pathfinder Experiment Telescope’. In Infrared and Millimeter Waves, 2007 and the 2007 15th International Conference on Terahertz Electronics. IRMMW-THz. Joint 32nd International Conference on, pp. 326–328. 152 J. F. Bell, et al. (2000). ‘Summary of the Elizabeth and Frederick White Conference on radio frequency interference mitigation strategies’. In J. B. . L. Kewley (ed.), The Elizabeth & Fredrick White Conference on Radio Frequency Interference Mitigation Stratergies. 24 J. F. Bell, et al. (2001). ‘Base Band Data for Testing Interference Mitigation Algorithms’. PASA 18:105–113. 31, 32 N. Bennert, et al. (2009). ‘A Search for H2O Megamasers in High-z Type-2 Active Galactic Nuclei’. ApJ 695:276–286. 77, 80 S. Bianchi, et al. (2012). ‘AGN Obscuration and the Unified Model’. Advances in Astronomy 2012. 4, 6, 92 M. D. Bicay, et al. (1995). ‘A multifrequency radio continuum and IRAS faint source survey of markarian galaxies’. ApJS 98:369–440. 101 J. Binney & S. Tremaine (2008). Galactic Dynamics: Second Edition. Princeton University Press. 118, 220, 221 R. D. Blandford & D. G. Payne (1982). ‘Hydromagnetic flows from accretion discs and the production of radio jets’. MNRAS 199:883–903. 6, 149 R. D. Blandford & R. L. Znajek (1977). ‘Electromagnetic extraction of energy from Kerr black holes’. MNRAS 179:433–456. 149 J. A. Braatz, et al. (2009). ‘Cosmology with Water-vapor Megamasers’. In Astro2010: The Astronomy and Astrophysics Decadal Survey, vol. 2010 of ArXiv Astrophysics e-prints, p. 23. 11, 12, 125, 219, 220 J. A. Braatz & N. E. Gugliucci (2008). ‘The Discovery of Water Maser Emission from Eight Nearby Galaxies’. ApJ 678:96–101. 9, 77, 91, 92, 93, 94, 97, 104, 105, 106, 107, 121 J. A. Braatz, et al. (2010). ‘The Megamaser Cosmology Project. II. The Angular-diameter Distance to UGC 3789’. ApJ 718:657–665. 94, 102, 106, 108, 110, 127, 132, 136, 140, 212, 215 J. A. Braatz, et al. (1996). ‘A Survey for H 2O Megamasers in Active Galactic Nuclei. I. Observations’. ApJS 106:51. 126, 146 J. A. Braatz, et al. (1997). ‘A Survey for H 2O Megamasers in Active Galactic Nuclei. II. A Comparison of Detected and Undetected Galaxies’. ApJS 110:321. 9, 77 A. E. Bragg, et al. (2000). ‘Accelerations of Water Masers in NGC 4258’. ApJ 535:73–89. 10, 108, 130, 217 A. F. Bridle & E. W. Greisen (1994). ‘The NRAO AIPS Project – A Summary’. Technical Memo AIPS Memo 87, National Radio Astronomical Observatory, Charlottesville, VA. 36, 49, 94, 111, 130, 134 F. H. Briggs, et al. (2000). ‘Removing Radio Interference from Contaminated Astronomical Spectra Using an Independent Reference Signal and Closure Relations’. AJ 120:3351–3361. 62, 63 F. H. Briggs & J. Kocz (2005a). ‘Overview of technical approaches to radio frequency interference mitigation’. Radio Science 40:5. 24 F. H. Briggs & J. Kocz (2005b). ‘Overview of Technical Approaches to RFI Mitigation’. ArXiv Astrophysics e-prints . 58 A. E. Broderick, et al. (2014). ‘Testing the No-hair Theorem with Event Horizon Telescope Observations of Sagittarius A*’. ApJ 784:7. 175 L. F. Brown, et al. (1989). ‘Global fringe fitting for polarization VLBI’. AJ 97:1522–1531. 172 A. Brunthaler, et al. (2005). ‘Atmosphere-Corrected Phase-Referencing’. In J. Romney & M. Reid (eds.), Future Directions in High Resolution Astronomy, vol. 340 of Astronomical Society of the Pacific Conference Series, p. 455. 95, 112, 133 P. Castangia, et al. (2013). ‘New Compton-thick AGN in the circumnuclear water maser hosts UGC3 789 and NGC 6264’. ArXiv e-prints . 82 H. Chamberlin (1985). Musical Applications of Microprocessors. Hayden Books, 2 edn. 37 R. Chellappa & S. Theodoridis (2013). Academic Press Library in Signal Processing: Volume 3: Array and Statistical Signal Processing. Academic Press. 59 G. Chen & B. Ratra (2011). ‘Median Statistics and the Hubble Constant’. PASP 123:1127–1132. 146 E. Churchwell, et al. (1977). ‘Detection of H2O maser emission in the Galaxy M 33’. A&A 54:969–971. 8 R. Cid Fernandes, et al. (2004). ‘The star formation history of Seyfert 2 nuclei’. MNRAS 355:273–296. 127 M. J. Claussen, et al. (1998). ‘The Water Masers in the Elliptical Galaxy NGC 1052’. ApJ 500:L129. 92 T. Coleman & Y. Li (1996). ‘An Interior Trust Region Approach for Nonlinear Minimization Subject to Bounds’. SIAM Journal on Optimization 6(2):418–445. 118, 137 S. Collin, et al. (2006). ‘Systematic effects in measurement of black hole masses by emission-line reverberation of active galactic nuclei: Eddington ratio and inclination’. A&A 456:75–90. 124 J. J. Condon, et al. (2002). ‘Radio Sources and Star Formation in the Local Universe’. AJ 124:675–689. 47, 106 J. J. Condon, et al. (1998). ‘The NRAO VLA Sky Survey’. AJ 115:1693–1716. 101, 106 J. J. Condon, et al. (1991). ‘Compact starbursts in ultraluminous infrared galaxies’. ApJ 378:65–76. 98 J. E. Conway & P. R. Blanco (1995). ‘H i Absorption Toward the Nucleus of the Powerful Radio Galaxy Cygnus A: Evidence for an Atomic Obscuring Torus?’. ApJ 449:L131. 47, 51, 52 E. A. Corbett, et al. (2003). ‘COLA. II. Radio and Spectroscopic Diagnostics of Nuclear Activity in Galaxies’. ApJ 583:670–688. 94 T. Cornwell & E. B. Fomalont (1989). ‘Self-Calibration’. In R. A. Perley, F. R. Schwab, & A. H. Bridle (eds.), Synthesis Imaging in Radio Astronomy, vol. 6 of Astronomical Society of the Pacific Conference Series, p. 185. 95 S. Crandall & B. Ratra (2013). ‘Median statistics cosmological parameter values’. ArXiv e-prints . 146 J. Dattorro (1997). ‘Effect Design: Part 1 Reverberator and Other Filters’. AES Journal 45(9):660–684. 37, 38 M. L. Davies, et al. (2013). ‘The radio source count at 93.2 GHz from observations of 9C sources using AMI and CARMA’. MNRAS 430:1961–1969. 95 T. M. Davis & C. H. Lineweaver (2004). ‘Expanding Confusion: Common Misconceptions of Cosmological Horizons and the Superluminal Expansion of the Universe’. Publications of the Astron. Soc. Australia 21:97–109. 214, 222 G. de Vaucouleurs, et al. (1991). Third Reference Catalogue of Bright Galaxies. Volume I: Explanations and references. Volume II: Data for galaxies between 0h and 12h. Volume III: Data for galaxies between 12h and 24h. Springer, New York, NY (USA). 83, 105, 126, 212 H. Dejonghe (1987). ‘A completely analytical family of anisotropic Plummer models’. MNRAS 224:13–39. 118, 213, 220 A. Deller (2010). ‘Software correlators as testbeds for RFI algorithms’. In RFI Mitigation Workshop PoS (RFI2010) 35. 34 A. T. Deller, et al. (2011). ‘DiFX-2: A More Flexible, E�cient, Robust, and Powerful Software Correlator’. PASP 123:275–287. 30, 34, 156 F. X. Desert & M. Dennefeld (1988). ‘The link between IRAS spectra and near-infrared emission features in external galaxies’. A&A 206:227–236. 106 J. Dexter & P. C. Fragile (2013). ‘Tilted black hole accretion disc models of Sagittarius A*: time-variable millimetre to near-infrared emission’. MNRAS 432:2252–2272. 4, 175 G. P. di Benedetto (2008). ‘The Cepheid distance to the Large Magellanic Cloud and NGC 4258 by the surface brightness technique and improved calibration of the cosmic distance scale’. MNRAS 390:1762–1776. 212 P. J. Diamond (1995). ‘VLBI Data Reduction in Practice’. In J. A. Zensus, P. J. Diamond, & P. J. Napier (eds.), Very Long Baseline Interferometry and the VLBA, vol. 82 of Astronomical Society of the Pacific Conference Series, p. 227. 50 P. J. Diamond, et al. (1999). ‘Global VLBI Observations of the Compact OH Megamaser Emission from III ZW 35 and IRAS 17208-0014’. ApJ 511:178–184. 53 S. G. Djorgovski, et al. (2008). ‘The Origins and the Early Evolution of Quasars and Supermassive Black Holes’. In H. Kleinert, R. T. Jantzen, & R. Ru�ni (eds.), The Eleventh Marcel Grossmann Meeting On Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories, pp. 340–367. 221 S. S. Doeleman, et al. (2012). ‘Jet-Launching Structure Resolved Near the Supermassive Black Hole in M87’. Science 338:355–. 4, 6, 150, 151, 175 M. A. Dopita & R. S. Sutherland (2003). Astrophysics of the diffuse universe. Springer. 96 R. J. H. Dunn, et al. (2010). ‘The radio properties of a complete, X-ray selected sample of nearby, massive elliptical galaxies’. MNRAS 404:180–197. 61 B. Efron & G. Gong (1983). ‘A Leisurely Look at the Bootstrap, the Jackknife, and Cross-Validation’. The American Statistician 37(1):36–48. 137 M. Elitzur (ed.) (1992). Astronomical masers, vol. 170 of Astrophysics and Space Science Library. 7 M. Elitzur (2007). ‘Recent developments in maser theory’. In J. M. Chapman & W. A. Baan (eds.), IAU Symposium, vol. 242 of IAU Symposium, pp. 7–16. 7 M. Elitzur (2012). ‘On the Unification of Active Galactic Nuclei’. ApJ 747:L33. 6 M. Elitzur & T. de Jong (1978). ‘A model for the maser sources associated with H II regions’. A&A 67:323–332. 9 M. Elitzur & I. Shlosman (2006). ‘The AGN-obscuring Torus: The End of the “Doughnut” Paradigm?’. ApJ 648:L101–L104. 6 S. W. Ellingson (2005). ‘Introduction to special section on Mitigation of Radio Frequency Interference in Radio Astronomy’. Radio Science 40:5. 24 A. P. Fairall (1986). ‘Some new bright southern Seyfert galaxies’. MNRAS 218:453–455. 126 X. Fan, et al. (2006). ‘Constraining the Evolution of the Ionizing Background and the Epoch of Reionization with z˜6 Quasars. II. A Sample of 19 Quasars’. AJ 132:117–136. 4 V. L. Fish, et al. (2011). ‘1.3 mm Wavelength VLBI of Sagittarius A*: Detection of Time-variable Emission on Event Horizon Scales’. ApJ 727:L36. 150, 175 D. J. Fixsen, et al. (1996). ‘The Cosmic Microwave Background Spectrum from the Full COBE FIRAS Data Set’. ApJ 473:576. 141 L. Flöer, et al. (2010). ‘RFI mitigation for the Effelsberg Bonn HI Survey (EBHIS)’. In RFI Mitigation Workshop (RFI2010) 42. 64 D. T. Frayer, et al. (1998). ‘OH satellite-line masers in the nucleus of NGC 253’. AJ 115:559. 77 W. L. Freedman, et al. (2012). ‘Carnegie Hubble Program: A Mid-infrared Calibration of the Hubble Constant’. ApJ 758:24. 123 A. M. Fridman, et al. (2005). ‘The orientation parameters and rotation curves of 15 spiral galaxies’. A&A 430:67–81. 103 P. A. Fridman & W. A. Baan (2001). ‘RFI mitigation methods in radio astronomy’. A&A 378:327–344. 24 D. C. Gabuzda & T. V. Cawthorne (2000). ‘VLBI polarization images of eight compact active galactic nuclei at �=1.3cm’. MNRAS 319:1056–1066. 149, 163 J. F. Gallimore, et al. (2004). ‘The Parsec-Scale Radio Structure of NGC 1068 and the Nature of the Nuclear Radio Source’. ApJ 613:794–810. 47 J. F. Gallimore, et al. (1996). ‘H 2O and OH Masers as Probes of the Obscuring Torus in NGC 1068’. ApJ 462:740. 46, 47, 48, 52, 53, 77, 92 T. Garn, et al. (2007). ‘Deep 610-MHz Giant Metrewave Radio Telescope observations of the Spitzer extragalactic First Look Survey field - I. Observations, data analysis and source catalogue’. MNRAS 376:1251–1260. 39, 54 M. A. Garrett & C. Greenwood (2012). ‘Resolving The Sky (RTS 2012) - Radio Interferometry: Past, Present and Future’. In Resolving The Sky - Radio Interferometry: Past, Present and Future. 16 R. W. Garwood, et al. (1987). ‘Arecibo observations of IRAS galaxies at 21 and 18 centimeters’. ApJ 322:88–100. 83 R. Giovanelli & M. P. Haynes (1993). ‘A survey of the Pisces-Perseus supercluster. VI - The declination zone +15.5 deg to 21.5 deg’. AJ 105:1271–1290. 85 M. Gliozzi, et al. (2003). ‘On the origin of the X-rays and the nature of accretion in NGC 4261’. A&A 408:949–959. 84 J. D. Goldader, et al. (1997). ‘Heavily Obscured Star Formation in the II ZW 96 Galaxy Merger’. AJ 113:1569–1579. 85 O. Gonz´alez-Mart´ın, et al. (2009). ‘Fitting Liner Nuclei within the Active Galactic Nucleus Family: A Matter of Obscuration?’. ApJ 704:1570–1585. 84, 90 J. E. Greene, et al. (2010). ‘Precise Black Hole Masses from Megamaser Disks: Black Hole-Bulge Relations at Low Mass’. ApJ 721:26–45. 11, 104, 121, 124, 125, 127, 138, 145, 196 L. J. Greenhill (2007). ‘Masers in AGN environments’. In J. M. Chapman & W. A. Baan (eds.), IAU Symposium, vol. 242 of IAU Symposium, pp. 381–390. 8 L. J. Greenhill, et al. (2003). ‘A Warped Accretion Disk and Wide-Angle Outflow in the Inner Parsec of the Circinus Galaxy’. ApJ 590:162–173. 6, 83, 84 L. J. Greenhill, et al. (2008). ‘Prevalence of High X-Ray Obscuring Columns among AGNs that Host H2O Masers’. ApJ 686:L13–L16. 78 E. Groten (2004). ‘Fundamental Parameters and Current (2004) Best Estimates of the Parameters of Common Relevance to Astronomy, Geodesy, and Geodynamics by Erwin Groten, IPGD, Darmstadt’. Journal of Geodesy 77(10-11):724–797. 22 M. A. Gurwell, et al. (2007). ‘Monitoring Phase Calibrators at Submillimeter Wavelengths’. In A. J. Baker, J. Glenn, A. I. Harris, J. G. Mangum, & M. S. Yun (eds.), From Z-Machines to ALMA: (Sub)Millimeter Spectroscopy of Galaxies, vol. 375 of Astronomical Society of the Pacific Conference Series, p. 234. 151 R. Güsten, et al. (2006). ‘The Atacama Pathfinder EXperiment (APEX) - a new submillimeter facility for southern skies -’. A&A 454:L13–L16. 151 K. Hada, et al. (2011). ‘An origin of the radio jet in M87 at the location of the central black hole’. Nature 477:185–187. 150 M. P. Haynes, et al. (2011). ‘The Arecibo Legacy Fast ALFA Survey: The ff.40 H I Source Catalog, Its Characteristics and Their Impact on the Derivation of the H I Mass Fu
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/5643