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University of Groningen The Role of Neutral Hydrogen in the Evolution of Nearby Radio Galaxies Struve, Rolf Christian IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 2010 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Struve, R. C. (2010). The Role of Neutral Hydrogen in the Evolution of Nearby Radio Galaxies. s.n. Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license. More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne- amendment. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Download date: 05-10-2021 The Role of Neutral Hydrogen in the Evolution of Nearby Radio Galaxies Proefschrift ter verkrijging van het doctoraat in de Wiskunde en Natuurwetenschappen aan de Rijksuniversiteit Groningen op gezag van de Rector Magnificus, dr. F. Zwarts, in het openbaar te verdedigen op vrijdag 12 november 2010 om 14:45 uur door Rolf Christian Struve geboren op 3 november 1981 te Kiel, Duitsland Promotor: Prof. dr. J. M. van der Hulst Copromotores: Dr. R. Morganti Dr. T. A. Oosterloo Beoordelingscommissie: Prof. dr. P. D. Barthel Prof. dr. J. H. van Gorkom Dr. J. E. Conway ISBN: 978-90-367-4562-8 Printed version ISBN: 978-90-367-4563-5 Electronic version Imagination is more important than knowledge. (Albert Einstein) Cover: The image shows Centaurus A as observed with the Australia Telescope Compact Array at radio wavelengths. The cold gas (neutral hydrogen, orange col- ors) is located in a disk which is roughly perpendicular to the innermost radio lobes (in blue). These lobes get fueled with relativistic plasma by the active black hole in the centre. The background displays the light emission at optical wavelengths (image kindly provided by Robert Gendler). The image on the backside shows the Westerbork Synthesis Radio Telescope observing the univese. Phote taken by me in 2006. Printed by: F&N Boekservice, Amsterdam, the Netherlands Contents 1 Introduction 9 1.1 From Black Holes to Active Galactic Nuclei ................ 9 1.2 Radio Galaxies ................................ 12 1.2.1 Different classes of radio sources .................. 12 1.2.2 Triggering mechanisms ....................... 13 1.2.3 Previous H I work .......................... 16 1.3 This thesis ................................... 17 1.3.1 Open questions and goals of this study .............. 17 1.3.2 Outline of the thesis ......................... 19 2 Large-scale H I structures in and around nearby radio galaxies 21 2.1 Introduction .................................. 22 2.2 Previous environment studies ....................... 23 2.3 The sample .................................. 25 2.3.1 Sample properties .......................... 25 2.3.2 Definition of environment ..................... 26 2.3.3 Companions detected in the optical band ............. 28 2.3.4 Limitations of the sample ...................... 28 2.3.5 Observations and follow-up .................... 32 2.4 Summary of the H I properties of the radio-loud sample ........ 34 2.5 The H I environment: Results ........................ 39 2.6 Discussion ................................... 48 2.7 Summary ................................... 49 2.A Appendix: Tables and total intensity maps ................ 51 3 Centaurus A: morphology and kinematics of the H I 65 3.1 Introduction .................................. 66 3.2 Observations and data reduction ...................... 68 3.3 Results ..................................... 71 3.3.1 The structure of the H I emission .................. 71 3.3.2 H I in absorption ........................... 74 3.3.3 Two newly discovered H I clouds in the environment of Cen- taurus A ............................... 77 3.4 The H I model ................................. 77 3.5 Discussion ................................... 81 6 3.5.1 Modelling implications: The large-scale H I distribution . ... 82 3.5.2 Merger and different phases of radio activity ........... 83 3.6 Summary ................................... 85 3.A Appendix: Channel maps .......................... 87 3.B Appendix: Is Centaurus A special? ..................... 96 3.B.1 Comparison with other early-type galaxies ............ 96 3.B.2 Comparison with other radio galaxies ............... 97 3.B.3 Conclusion .............................. 99 4 A circumnuclear disk of atomic hydrogen in Centaurus A 101 4.1 Introduction .................................. 101 4.2 The ATCA Data ................................ 102 4.3 Broad nuclear H I absorption ........................ 102 4.3.1 A circumnuclear H I disk? ..................... 104 4.3.2 The nature of the absorbed continuum .............. 106 4.4 Conclusions .................................. 108 5 An H I absorbing circumnuclear disk in Cygnus A 109 5.1 Introduction .................................. 110 5.2 Observations ................................. 111 5.3 Results ..................................... 113 5.3.1 Continuum image .......................... 113 5.3.2 H I absorption ............................ 113 5.3.3 Modelling spatial variations in broad line opacity ....... 116 5.4 Discussion ................................... 119 5.4.1 A disk geometry for the broad absorption component ..... 119 5.4.2 Physical properties of the broad absorption component gas .. 120 5.4.3 Constraints on circumnuclear torus properties and relation to the H I disk .............................. 122 5.4.4 The narrow absorption component ................ 124 5.5 Summary ................................... 125 6 Cold gas in massive ETGs: The case of NGC 1167 127 6.1 Introduction .................................. 128 6.2 Observations and data reduction ...................... 130 6.3 Results ..................................... 131 6.3.1 NGC 1167 ............................... 131 6.3.2 The (H I) environment of NGC 1167 ................ 136 6.4 The search for an H I halo .......................... 137 6.4.1 Identifying halo gas ......................... 138 6.4.2 An upper limit to the H I halo ................... 140 6.5 Rotation curve ................................ 140 6.5.1 Large-scale streaming motions ................... 141 6.5.2 Mass models ............................. 144 6.6 Discussion ................................... 144 6.6.1 Formation of the H I disk ...................... 144 7 6.6.2 The absence of an H I halo . .................... 147 6.6.3 Streaming motions, rotation curve and H I density distribution 148 6.7 Summary ................................... 149 6.A Appendix: Channel maps .......................... 150 7 The intriguing radio source B2 0258+35 155 7.1 Introduction .................................. 155 7.2 A 240-kpc radio relic structure ....................... 156 7.3 The nuclear H I absorption ......................... 157 7.3.1 VLA observations and data reduction ............... 157 7.3.2 Results ................................. 158 7.4 Discussion ................................... 164 7.4.1 The circumnuclear gas structure .................. 164 7.4.2 Recurrent phases of radio activity ................. 166 7.5 Summary ................................... 167 8 Summary and future perspectives 169 8.1 H I properties of radio galaxies – results of this thesis .......... 169 8.1.1 300 kpc scale: environment ..................... 169 8.1.2 Tens of kpc scale: disk structures .................. 170 8.1.3 100 pc scale: circumnuclear structures ............... 170 8.1.4 The origin of cold gas in massive early-type galaxies ...... 171 8.2 Main conclusions and open questions ................... 172 8.3 Outlook .................................... 174 Nederlandse samenvatting 187 Acknowledgements 197 8 1 Introduction Approximately 60 years ago, in the late 1940’s, several radar devices – previously used by the military – were transformed into research instruments that offered the possibility to observe and study cosmic objects at previously unexplored frequen- cies. The new instruments introduced a new field in astronomy, which enabled scien- tists to observe the universe with “radio eyes”. First targets were the sun and strong radio emitters located in the Galaxy. However, extragalactic radio emitters were soon detected as well. Among the first three identified extragalactic objects were Virgo A, Centaurus A and Cygnus A (see, e.g., Bolton & Stanley, 1948a,b; Bolton, 1948); these radio emitters are now known to be hosted by galaxies (called “radio galaxies”)1. Yet back in the 1940’s, the nature of these sources was still completely unknown; Walter Baade referred to Centaurus A as a “freak” while Harlow Shapley saw it as a “patho- logical specimen” because
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