University of Groningen
Nowhere to hide: identifying AGN in the faint radio sky
Radcliffe, Jack Frederick
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Radcliffe, J. F. (2019). Nowhere to hide: identifying AGN in the faint radio sky. University of Groningen.
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Nowhere to Hide:
Identifying AGN in the faint radio sky
Proefschrift
ter verkrijging van de graad van doctor aan de Rijksuniversiteit Groningen
op gezag van de
rector magnificus prof. dr. E. Sterken en in overeenstemming met
de beslissing van het College voor Promoties. en
ter verkrijging van de graad van Doctor of Philosophy aan de Faculty of Engineering and Physical Sciences van de
University of Manchester
De openbare verdediging zal plaatsvinden op dinsdag 23 april 2019 om 11:00 uur
door
Jack Frederick Radcliffe geboren op 27 oktober 1991 te Shrewsbury, Verenigd Koninkrijk
Promotores Prof. dr. P.D. Barthel Prof. dr. M.A. Garrett Co-promotores Dr. R.J. Beswick Dr. T.W.B. Muxlow Beoordelingscommissie Prof. dr. C. Jackson Prof. dr. J.P. McKean Prof. dr. R.A. Windhorst Prof. dr. A.A. Zijlstra
Kapteyn Institute - PhD thesis 2019 ISBN: 978-94-034-1507-9
ISBN: 978-94-034-1506-2 (electronic version)
The work described in this thesis was performed in the research group at the Kapteyn Astro-nomical Institute at the University of Groningen, the Netherlands, and the Jodrell Bank Centre for Astrophysics at the University of Manchester, United Kingdom.
Cover design: J.F. Radcliffe
Cover image credits: (AGN inset) Centaurus A - (Optical) ESO / WFI; (Submillimetre) MPIfR / ESO / APEX / A.Weiss et al.; (X-ray) NASA / CXC / CfA / R.Kraft et al.
(AGN inset) 3C66B - NRAO / AUI 2006. (AGN inset) 3C31 - NRAO / AUI 2006. (AGN inset) 3C296 - NRAO / AUI 2006.
(Lovell telescope) - Pete Birkinshaw, cc-by-2.0 (edited by J.F. Radcliffe). (WSRT) - ASTRON 2017 (edited by J.F. Radcliffe).
(Background) GOODS-N - NASA, ESA, G. Illingworth (University of California, Santa Cruz), P. Oesch (University of California, Santa Cruz; Yale University), R. Bouwens and I. Labbé (Leiden University), and the Science Team.
‘Man is not worried by real problems so much as by his imagined anxieties about real problems’ — Epictetus
Contents
List of Figures ix
List of Tables xiii
Summary xv
Samenvatting xix
1 Introduction 1
1.1 Motivation . . . 1
1.2 Very Long Baseline Interferometry. . . 3
1.2.1 Wide-field VLBI . . . 6
1.2.2 Fundamentals of radio interferometry . . . 6
1.2.3 Challenges . . . 12
1.2.4 Solutions . . . 16
1.2.5 Open Issues . . . 19
1.3 Active Galactic Nuclei . . . 20
1.3.1 The key components . . . 21
1.3.2 The role of AGN in galaxy evolution . . . 22
1.3.3 Identifying the AGN contribution . . . 28
1.3.4 Radio and the role of high resolution surveys . . . 33
1.3.5 Science goals . . . 36
Bibliography . . . 37
2 Multi-source self-calibration 43 2.1 Introduction . . . 45
2.2 HDF-N wide-field VLBI observations . . . 47
2.3 Multi-source self-calibration . . . 49 2.4 Results . . . 53 2.5 Future applications . . . 54 2.6 Conclusions . . . 57 Bibliography . . . 57 v
vi Contents
3 Nowhere to Hide - I. Initial catalogue and radio properties 59
3.1 Introduction . . . 61
3.2 Observations & data reduction . . . 63
3.2.1 EVN observations. . . 63
3.2.2 Source detection methodology . . . 69
3.2.3 VLA observations . . . 72
3.3 EVN primary beam correction . . . 72
3.4 Catalogue description . . . 74
3.5 Results and discussion . . . 80
3.5.1 Redshifts . . . 80
3.5.2 Astrometry . . . 80
3.5.3 Comparison to other VLBI surveys . . . 81
3.5.4 Radio properties of the VLBI selected population . . . 83
3.6 Conclusions . . . 89
3.A Astrometry of J1234+619 . . . 90
Bibliography . . . 92
4 Nowhere to Hide - II. AGN selection techniques and host galaxy prop-erties 95 4.1 Introduction . . . 97
4.2 Observations and catalogues . . . 99
4.2.1 Infra-red . . . 102
4.2.2 X-rays . . . 104
4.2.3 Radio . . . 105
4.2.4 Host morphologies . . . 105
4.3 AGN classification techniques . . . 106
4.3.1 Optical / UV . . . 106 4.3.2 Infra-red . . . 108 4.3.3 X-rays . . . 115 4.3.4 Radio excess. . . 117 4.3.5 Radio variability . . . 121 4.3.6 Radio morphologies . . . 122 4.3.7 Summary . . . 122
4.4 Uniqueness and overlap of AGN between different wavelengths . . . . 128
4.4.1 The VLBI-selected sample and the nature of this population . . 128
Contents vii
4.5 Radio emission in RE-AGN . . . 136
4.5.1 Stacking procedure . . . 136
4.5.2 Stacking results . . . 138
4.5.3 Stacking discussion . . . 139
4.6 Conclusions . . . 142
4.A Detailed descriptions of VLBI detected objects . . . 143
4.A.1 Previous VLBI detections. . . 147
4.A.2 New VLBI detections . . . 153
4.A.3 Non-detection: J123642+621545 . . . 161
Bibliography . . . 162
5 The transient and variableµJy radio sky across multiple decades 167 5.1 Introduction . . . 169
5.2 Data . . . 171
5.2.1 VLA observations . . . 171
5.2.2 JVLA observations . . . 173
5.2.3 Off-axis source removal . . . 174
5.2.4 Imaging . . . 175
5.3 Defining a variable sample . . . 176
5.3.1 Source extraction . . . 176
5.3.2 uv coverage . . . 180
5.3.3 Reference frequency . . . 180
5.3.4 Absolute flux scaling . . . 182
5.3.5 Variability definition . . . 182 5.3.6 Summary . . . 184 5.4 Results . . . 185 5.4.1 Variable sources. . . 185 5.4.2 Transient sources . . . 187 5.5 Discussion . . . 189
5.5.1 Comparison to other variability surveys . . . 189
5.5.2 Sources of variability . . . 190
5.5.3 J123742.33+621518.27 - a possible radio supernova? . . . 195
5.5.4 Transient upper limits . . . 199
5.6 Conclusions . . . 201
Bibliography . . . 202
6 Conclusions 205 6.1 Chapter 2: Multi-source self-calibration . . . 205 6.2 Chapter 3: Nowhere to Hide - I. Initial catalogue and radio properties . 206
viii Contents
6.3 Chapter 4: Nowhere to Hide - II. AGN selection techniques and host galaxy properties . . . 207 6.4 Chapter 5: The transient and variable µJy radio sky across multiple
decades . . . 208 Bibliography . . . 209
7 Future prospects 211
7.1 Extending multi-source self-calibration: CASA and direction dependent calibration . . . 211 7.2 VLBI-selected AGN in the microJy flux regime . . . 213 7.3 Identifying radio AGN for the MIGHTEE survey . . . 215 7.4 AGN feedback using integrated EVN and e-MERLIN observations . . . 215 7.5 SKA-VLBI . . . 217 Bibliography . . . 217
List of Figures
1 The faint radio sky above the Green Bank radio telescope. . . xv
2 The 76m Lovell Telescope . . . xvi
3 The Great Observatories Origins Deep-North (GOODS-N) as seen by the Hubble Space Telescope . . . xviii
4 De zwakke radiohemel boven de Green Bank-telescoop in de VS. . . xix
5 De Westerbork Synthesis Radio Telescoop (WSRT) . . . xx
6 Het veld Great Observatories Origins Deep-North (GOODS-N) . . . xxii
1.1 Composition of the extragalactic radio source populations from Padovani et al. (2015) . . . 2
1.2 The individual telescopes that make up the European VLBI Network and Very Long Baseline Array . . . 4
1.3 A diagram of a two element radio interferometer . . . 7
1.4 Illustration of time smearing. . . 14
1.5 An example of interferometer non-coplanarity. . . 15
1.6 An example wide-field VLBI survey using the multiple phase centre correlation technique to target the starburst galaxy M82. . . 18
1.7 Simplified diagram illustrating the main components of Active Galactic Nuclei from Heckman & Best (2014) . . . 23
1.8 Scaling relations between the central supermassive black hole and host galaxy properties which infers a co-evolution. . . 24
1.9 An example of negative AGN feedback in MS0735.6+7421 (McNamara et al., 2005) . . . 26
1.10 AGN selection using emission line ratios and infra-red selection tech-niques. . . 31
1.11 The star formation rate density (SFRD) history from Novak et al. (2017). 34 2.1 The point source model of J123646+621405 and theuv-stacked 1 Jy source used for self-calibration . . . 46
2.2 Noise distribution profiles used to determine the detection threshold. . 48
x List of Figures
2.3 Compact radio source J123659+621833 before and after MSSC. . . 50
2.4 Diagram of the MSSC algorithm and its implementation in AIPS. . . 55
3.1 Sources / sub-fields targeted by these GOODS-N observations. . . 66
3.2 R.m.s. sensitivity for our 1.6 GHz EVN observations after primary beam correction. . . 67
3.3 Composite image of 1.4 GHz WSRT radio-KPNO optical overlay of the GOODS-N field, centred on the HDF-N (Garrett et al., 2000), surrounded by postage stamp images of the 1.6 GHz 31 VLBI detected sources presented in this chapter. . . 70
3.4 Redshift distribution for our detected VLBI sources. . . 78
3.5 Relative astrometric precision between Muxlow et al. (2005) and the EVN observations. . . 82
3.6 Radio power vs. redshift for our VLBI sources. . . 85
3.7 Brightness temperature distribution with respect to redshift. . . 87
3.8 Sky distribution of sources observed with e-MERLIN at 5 GHz. . . 90
4.1 Multi-wavelength coverage of a sub-set of observations in the GOODS-N field . . . 100
4.2 Spitzer IRAC AGN selection criteria for the VLBI detected sample. . . . 111
4.3 The Stern et al. (2005) IRAC selection scheme and the WISE 3-band AGN identification schemes . . . 113
4.4 The KI and KIM selection schemes (Messias et al., 2012). . . 116
4.5 AGN selection using the monochromatic radio excess parameters,q24 andq100 . . . 118
4.6 The total radio excess parameterqTIRfor those VLBI sources with FIR counterparts. . . 120
4.7 The breakdown of the AGN classification schemes with a VLBI-selected AGN sample. . . 130
4.8 The photon index against redshift for the X-ray detections illustrating the increase in obscuration at thez ∼ 2overdensity. . . 132
4.9 IR colour-colour plots for various AGN samples and classification techniques using a matched area with X-ray, IR and radio coverage. . . 133
4.10 The radio excess parameter (q24) for all of the 1.5 GHz VLA sources with24µmcounterparts. . . 134
4.11 Radio stacking on X-ray bright but radio quiet AGN. . . 137
4.12 q24against redshift for a sample of radio-quiet X-ray AGN. . . 140
4.13 HST F125W near-IR imaging of the host galaxies of the VLBI detected sources . . . 144
List of Figures xi
4.14 CFHT observations of the host galaxies of VLBI detected sources in the near-IR (Ks band) . . . 147 4.15 1.5 GHz observations of FR-I source J123656+615659 . . . 161 4.16 The host galaxy of VLBI variable source J123642+621545 . . . 162 5.1 1◦× 1◦ image of the 1996 VLA data illustrating the source removal
routine outlined in Section 5.2.3 . . . 172 5.2 Summary of the various source extraction tests performed usingPYBDSF. 177 5.3 Comparison between the 1.4 GHz (corrected using the in-band spectral
indices) and the 1.52 GHz fluxes of the JVLA 2018 epoch. . . 181 5.4 The two epoch comparison of the variability statistic,Vs, to the
modu-lation index,m. . . 183 5.5 Light curves for the variable candidates. . . 188 5.6 Spitzer IRAC AGN selection criteria for the variable candidate sample. 196 5.7 Type II supernovae / LLAGN candidate. . . 197 5.8 The transient normalised areal densities, and upper limits, with respect
to flux density. . . 200 7.1 Implementation of MSSC to provide direction-dependent calibration
for VLBI observations. . . 212 7.2 Theuv-coverages for the integrated EVN e-MERLIN observations of
the GOODS-N field (EVN project code EG078G; Radcliffe et al. in prep.). 214 7.3 J123642+621331 (z ∼ 2), a composite star-burst and AGN candidate
imaged using a combination of VLA, e-MERLIN and EVN data. . . 216 7.4 The angular resolution at 1.5 GHz provided by the current suite of
List of Tables
1.1 An overview of key strengths and weaknesses of AGN selection in multiple wavebands. . . 29 2.1 Comparison between standard phase referencing, single source
self-calibration and MSSC self-calibration techniques. . . 52 3.1 EG078B observing strategy. . . 64 3.2 1.6 GHz VLBI and 1.5 GHz VLA properties of the VLBI detected sources 75 3.3 Derived VLA & VLBI radio properties of the 31 GOODS-N AGN. . . 77 3.4 Phase calibrators used in the 5 GHz eMERLIN observations . . . 91 3.5 Positions and relative offsets of J1234+619 . . . 91 4.1 Multi-wavelength data available in the GOODS-N field that are used
in this analysis. . . 101 4.2 The number of multi-wavelength VLBI counterparts and the waveband
sensitivities. . . 107 4.3 IR AGN colour-colour selection scheme definitions. . . 109 4.4 AGN classification schemes. . . 123 4.5 A summary of the stacking resulted based upon the weighted mean
radio stack of X-ray selected AGN. . . 139 5.1 A summary of the individual VLA/JVLA epochs utilised in this chapter 170 5.2 A summary of the multi-wavelength properties and AGN classification
for the variable candidates. . . 191
