INVESTIGATING ACTIVE GALACTIC NUCLEI with LOW FREQUENCY RADIO OBSERVATIONS By
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INVESTIGATING ACTIVE GALACTIC NUCLEI WITH LOW FREQUENCY RADIO OBSERVATIONS by MATTHEW LAZELL A thesis submitted to The University of Birmingham for the degree of DOCTOR OF PHILOSOPHY School of Physics & Astronomy College of Engineering and Physical Sciences The University of Birmingham March 2015 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. Abstract Low frequency radio astronomy allows us to look at some of the fainter and older synchrotron emission from the relativistic plasma associated with active galactic nuclei in galaxies and clusters. In this thesis, we use the Giant Metrewave Radio Telescope to explore the impact that active galactic nuclei have on their surroundings. We present deep, high quality, 150–610 MHz radio observations for a sample of fifteen predominantly cool-core galaxy clusters. We in- vestigate a selection of these in detail, uncovering interesting radio features and using our multi-frequency data to derive various radio properties. For well-known clusters such as MS0735, our low noise images enable us to see in improved detail the radio lobes working against the intracluster medium, whilst deriving the energies and timescales of this event. Our excellent field of view allowed us to explore the point-source like radio AGN for a subsample of our clusters. We used additional optical and infra-red data to identify cluster members, remove radio contamination from star forming galaxies, and thus investigate the energetics of the many cluster galaxies. We find that low mass radio-loud AGN can easily quench the star formation at their core, and possibly enough to eject the gas from the system given some assumptions. We compare our observations with the results of cosmological hydrodynamical simulations (cosmo-OWLS), and explore the mechanical and binding energy levels over a large range of galaxy masses. We look at the radio powers of our sample and compare these to the published X-ray cavity powers. We find an improved relation from our integrated luminosities, allowing a more accurate estimation of jet powers when X-ray or radio observations are unavailable. The question of what radio jets are made of is still an unknown variable in AGN physics today. Our observations rule out a relativistic electron/positron plasma, we find that a heavier solution is required. Our deepest low-frequency radio observations of these well-known clusters will yield valuable information about the nature of feedback when combined with X-ray observations of comparable depth. We present results from such combined work in this thesis. Acknowledgements Family Friends Dr. Somak Raychaudhury Prof. Trevor Ponman Dr. Ian Stevens Prof. Matt Jarvis David Stops Dr. Ian McCarthy Dr. Chris Haines Dr. Ishwara Chandra Dr. Ewan O’Sullivan, Dr. Alastair Sanderson, Dr. Samuel George Contents 1 Radio galaxies in clusters 1 1.1 What causes radio emission? ............................ 1 1.1.1 Synchrotron radiation ........................... 2 1.1.2 What causes radio emission in galaxies? ................. 4 1.2 Active galactic nuclei ................................ 4 1.2.1 Basic model of extragalactic radio sources ................ 5 1.2.2 Radio source structures .......................... 5 1.3 Galaxy formation and evolution .......................... 7 1.3.1 Estimating black hole masses ....................... 8 1.3.2 Black hole scaling relations ........................ 10 1.4 Clusters of galaxies ................................. 12 1.4.1 Cool-cores and non-cool-cores ...................... 13 1.4.2 AGN feedback ................................ 14 1.4.3 AGN feedback modes ............................ 16 1.4.4 Environmental effects ........................... 20 1.5 Sample selection ................................... 21 2 Principles of imaging with radio telescopes 23 2.1 Detecting radio waves ................................ 23 2.2 Interferometric imaging ............................... 24 2.3 Sensitivity & uv–coverage ............................. 29 CONTENTS iii 2.4 The GMRT ...................................... 29 2.5 Radio frequency interference ............................ 34 2.6 Data Reduction ................................... 37 2.6.1 Preparation ................................. 37 2.6.2 Flagging & calibration ........................... 38 2.6.3 Imaging ................................... 43 2.6.4 Self-calibration ............................... 45 2.7 Stripe removal .................................... 47 2.8 Wide-field imaging ................................. 50 3 The energetics of the radio AGN population in clusters 52 3.1 Introduction ..................................... 52 3.2 GMRT Radio Observations & Reduction ...................... 54 3.2.1 Observations ................................ 54 3.2.2 Reduction .................................. 55 3.3 The source catalogue ................................ 57 3.3.1 Source extraction .............................. 57 3.3.2 Catalogue cross-correlation and matching ................ 58 3.3.3 Comparison with other radio catalogues ................. 61 3.4 Galaxy properties .................................. 63 3.4.1 LoCuSS ................................... 63 3.4.2 Star formation rates ............................ 64 3.4.3 X-ray data .................................. 66 3.4.4 Stellar masses ................................ 66 3.4.5 Binding energies .............................. 67 3.4.6 Radio analysis ................................ 68 3.4.7 Removing contamination from star-forming galaxy radio emission .. 68 3.4.8 Final AGN radio luminosities ....................... 73 3.5 Radio AGN in the galaxy population ........................ 75 CONTENTS iv 3.5.1 The radio-loud AGN fraction ....................... 75 3.5.2 The heating power of AGN ........................ 84 3.5.3 cosmo-OWLS simulations ......................... 85 3.5.4 Gas ejection by radio galaxies ....................... 88 3.5.5 Heating vs cooling for galaxies ...................... 95 3.6 Conclusions and further work ........................... 97 3.7 Radio AGN and their environment ......................... 100 3.7.1 Radio fraction as a function of its environment ............. 100 3.7.2 Heating vs cooling for clusters ...................... 101 4 The interaction between AGN and the intracluster medium 111 4.1 Cluster energetics .................................. 112 4.2 Spectral ageing .................................... 121 4.3 Radio lobe composition ............................... 125 4.4 Conclusions and further work ........................... 128 5 Low-frequency observations of radio galaxies in rich clusters 130 5.1 2A0335+096 ..................................... 130 5.2 MS0735.6+7421 .................................... 136 5.3 Hydra A ....................................... 147 5.4 Abell 2052 ...................................... 151 5.5 Abell 2218 ...................................... 154 5.6 Hercules A ...................................... 159 5.7 RXJ1720.1+2638 ................................... 162 5.7.1 SDSS J172027.49+263158.7 ......................... 164 5.7.2 SDSS J172107.89+262432.1 ......................... 169 5.8 A brief description of the other cluster observations ............... 172 5.8.1 Abell 478 .................................. 172 5.8.2 RBS797 .................................... 172 LIST OF REFERENCES v 5.8.3 Abell 1795 .................................. 175 5.8.4 Abell 1835 .................................. 175 5.8.5 Abell 2029 .................................. 177 5.8.6 Abell 2597 .................................. 177 6 Conclusions & further work 178 A Synchrotron model fits 181 List of References 192 List of Figures 1.1 Synchrotron emission spectrum .......................... 3 1.2 Images of an FR-I & FR-II source .......................... 7 1.3 Measuring the motion of stars near the galactic centre .............. 9 1.4 M–σ plots ...................................... 11 1.5 The cool-core/non-cool-core cluster bimodality. ................. 15 2.1 The u v w imaging geometry. .......................... 27 ( , , ) 2.2 Using many antennae to make up a large array. ................. 28 2.3 uv–coverage of a 10 minute snapshot of MS0735. ................ 30 2.4 uv–coverage of a 6 hour observation of MS0735. ................. 31 2.5 The GMRT array configuration. .......................... 33 2.6 One of the GMRT dishes in the central square. .................. 35 2.7 The GMRT radio frequency spectrum from 0–500 MHz. ............. 36 2.8 Output from the u�ℐu�u� tool listr ......................... 38 2.9 The tvflg tool .................................... 39 2.10 snplt: phase ..................................... 40 2.11 snplt: amplitude .................................. 40 2.12 Bandpass plot of MS0735 .............................. 41 2.13 Flagging RFI with tvflg .............................. 42 2.14 imagr in interactive mode. ............................. 46 2.15 The snplt after self-calibration ........................... 48 LIST OF FIGURES