LOFAR-UK a Science Case for UK Involvement in LOFAR
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LOFAR-UK A science case for UK involvement in LOFAR Assembled and edited on behalf of the LOFAR-UK consortium by Philip Best December 2007 Contributors: Paul Alexander (Cambridge), David Bacon (Edinburgh/Portsmouth), David Bersier (Liverpool JMU), Philip Best (Edinburgh), Rob Beswick (Manchester), Andy Breen (Aberyst- wyth), Elias Brinks (Hertfordshire), Catherine Brocksopp (UCL/MSSL), Sandra Chapman (War- wick), Michele Cirasuolo (Edinburgh), Judith Croston (Hertfordshire), Owain Davies (RAL), Tom Dwelly (Southampton), Steve Eales (Cardiff), Alastair Edge (Durham), Brian Ellison (RAL), Rob Fender (Southampton), Lyndsay Fletcher (Glasgow), Martin F¨ullekrug (Bath), Simon Garrington (Manchester), Dave Green (Cambridge), Martin Haehnelt (Cambridge), Martin Hardcastle (Hert- fordshire), Richard Harrison (RAL), Faridey Honary (Lancaster), Rob Ivison (ATC), Neal Jackson (Manchester), Matt Jarvis (Hertfordshire), Christian Kaiser (Southampton), Joe Khan (Glasgow), Hans-Rainer Kl¨ockner (Oxford), Eduard Kontar (Glasgow), Michael Kramer (Manchester), Cedric Lacey (Durham), Mark Lancaster (UCL), Tom Maccarone (Southampton), Alec MacKinnon (Glas- gow), Ross McLure (Edinburgh), Avery Meiksin (Edinburgh), Cathryn Mitchell (Bath), Bob Nichol (Portsmouth), Will Percival (Portsmouth), Robert Priddey (Hertfordshire), Steve Rawlings (Ox- ford), Chris Simpson (Liverpool JMU), Ian Stevens (Birmingham), Tom Theuns (Durham), Phil Uttley (Southampton), Peter Wilkinson (Manchester), Graham Woan (Glasgow) Contents 1 Executive Summary 1 2 Introduction 3 2.1 International extensions of LOFAR . .......... 4 2.2 Thisdocument .................................... ... 6 3 LOFAR in the context of UK radio astronomy 7 3.1 The University of Manchester and Jodrell Bank Observatory ............. 7 3.2 The University of Cambridge and the Mullard Radio Astronomy Observatory . 8 3.3 LOFAR-UK as a stepping-stone to the SKA . ...... 9 4 LOFAR-UK and the Epoch of Reionisation 10 4.1 Introduction: The Epoch of Reionisation . ............ 10 4.2 Observational 21cm signatures of Reionisation . ............... 13 4.3 Removal of foreground signals and detection strategies ................. 15 4.4 Reionisation and galaxy formation . .......... 16 4.5 ReionisationandtheUK. ...... 17 5 Deep Extragalactic Surveys with LOFAR-UK 18 5.1 Complementary observations of LOFAR deep survey regions.............. 18 5.1.1 Optical and near-IR surveys of the LOFAR survey regions ........... 19 5.1.2 Westerbork and GMRT surveys of ‘LOFAR-deep’ . ....... 21 5.2 Starforming galaxies in the deepest radio surveys . ............... 22 5.2.1 The star-formation history of the Universe . .......... 24 5.2.2 Comparison with sub-millimetre and mid-to-far infrared surveys . 25 5.2.3 Gigamasers: pinpointing luminous starbursts at very high redshift . 27 5.2.4 Extending the radio–infrared correlation . ............ 28 5.3 Radio–loud AGN and their influence on galaxies and the large–scale environment . 29 5.3.1 The nature and evolution of radio–AGN feedback on galaxyscales . 29 5.3.2 FeedbackfromFRIIs?. 31 5.3.3 AGN feedback and the larger–scale environment . .......... 31 5.3.4 Radio galaxy structure and electron energy distributions............ 33 5.3.5 High redshift quasars and the link to star formation . ............ 34 5.3.6 Evolution of the radio luminosity function and high-redshift radio galaxies . 34 5.3.7 Powerful radio galaxies within the Epoch of Reionisation ........... 35 5.4 Cosmology with the LOFAR sky surveys . ........ 35 5.4.1 Spectroscopic follow-up of LOFAR-deep, and Dark Energy .......... 35 i 5.4.2 Strong gravitational lensing . ........ 36 5.4.3 WeaklensingwithLOFAR . 37 5.5 LOFARstudiesoflocalgalaxies. ......... 38 5.5.1 Low frequency observations of nearby starburst galaxies ............ 38 5.5.2 Jet-powered radio nebulae around extragalactic microquasars . 40 5.6 CosmicMagnetism ................................. 41 6 LOFAR-UK and Radio Transients 42 6.1 X-raybinaries/microquasars . ........ 42 6.2 AGN outbursts and variability . ........ 43 6.3 Gamma-raybursts .................................. 44 6.4 Pulsarsandrelatedphenomena . ........ 46 6.4.1 Extragalacticpulsars. ...... 49 6.5 Extrasolarplanets ............................... ...... 49 6.6 Search for Extraterrestrial Intelligence . ............... 51 6.7 ExplorationoftheUnknown. ....... 52 7 Ultra-High Energy Cosmic Rays and Neutrinos with LOFAR-UK 54 8 Solar and Heliospheric Physics with LOFAR-UK 56 8.1 SolarFlares..................................... 57 8.2 CoronalMassEjections ............................ ...... 58 8.3 Coronalshockwaves ............................... ..... 58 8.4 Non-flaringactiveregionenergyrelease . ........... 60 8.5 Radar mapping of the solar corona, and plasma turbulence .............. 60 8.6 Radio scintillation observations of the 3D solar wind . ................ 61 8.7 Riometric Observations of the terrestrial space environment .............. 64 8.8 LOFARasanionosphericsensor . ....... 65 8.9 Radio from Lightning Flashes and Cosmic Rays . ........... 65 8.10 Otherscienceareas.............................. ....... 66 9 LOFAR-UK as a stand-alone array 67 9.1 Pulsar observations with individual LOFAR stations . ............... 67 9.2 Solar observations with individual LOFAR stations . ............... 67 9.3 Heliospheric Physics with individual LOFAR stations . ................ 68 9.4 Ionospheric diagnostics with individual LOFAR stations................ 68 9.5 Correlating E-LOFAR stations for early long-baseline surveys ............. 69 10 Technical Case 70 ii 10.1 The locations of UK LOFAR stations . ......... 70 10.2Datatransport .................................. ..... 73 10.3 Long-baselinecalibration. .......... 74 10.4 Operational requirements for Solar and Heliospheric observations with LOFAR . 74 10.4.1 Solar observational requirements . .......... 75 10.4.2 Heliospheric observation requirements . ............ 75 11 The LOFAR-UK Consortium 77 11.1 Consortium members and management . ......... 77 11.2 Estimated costs and funding of LOFAR-UK . ......... 78 iii iv 1 Executive Summary LOFAR, the Low-Frequency Array, is a next-generation software-driven radio telescope operating between 30 and 240 MHz, currently under construction in the Netherlands. This low frequency radio band is one of the few largely unexplored regions of the electromagnetic spectrum. The sensitivity and angular resolution offered by LOFAR will be two to three orders of magnitude better than existing telescopes, and as such it will open up this new window on the Universe. LOFAR will impact on a broad range of astrophysics, from cosmology to solar system studies: it will conduct the first studies of the Epoch of Reionisation, carry out the deepest large–sky radio source surveys ever, revolutionise the study of transient phenomena, make measurements of ultra-high energy cosmic rays via radio emission from air showers, and investigate the radio signatures of solar and interplanetary activity. In addition, history indicates that exploring new frequency windows has always led to unexpected discoveries. There is growing European involvement in LOFAR, driven by the need to add stations far from the main core in order to improve angular resolution. LOFAR-UK is a project aimed at cementing UK participation in LOFAR via the operation of four stations within the UK, as part of a European expansion including Germany, France, Sweden and probably other European countries. LOFAR- UK ground stations will allow the highest angular resolution LOFAR observations, reaching sub- arcsecond scales at the highest LOFAR frequencies, and as a result will also improve the (confusion- limited) sensitivity limit of the telescope for deep surveys. UK stations will also significantly enhance the instantaneous (u,v)-plane coverage, essential for snapshots of transient phenomena. LOFAR-UK will achieve involvement for UK astronomers in a world-leading science facility operat- ing in the immediate future. It will allow the UK to build up important scientific and technical ex- pertise in ‘next generation’ radio astronomy in preparation for the Square Kilometre Array (SKA). Noting the dramatic increase in the diversity of topics addressable with the next generation of radio telescopes, LOFAR-UK will play an important role in helping to broaden the UK community that has an interest in radio astronomy: one of the key features of the LOFAR-UK consortium is that it gathers together traditional ‘radio astronomy’ groups with groups with very limited experience in radio astronomy, but great interest in the new science to be achievable with LOFAR and the SKA. This White Paper outlines the strategic importance to the UK astronomy community of gaining involvement in the LOFAR project, the scientific interests of UK researchers in using the telescope, and the technical challenges that will need to be overcome. 1 2 2 Introduction LOFAR is a next-generation software-driven radio telescope currently under construction by AS- TRON in the Netherlands. LOFAR will explore the 30-240 MHz radio sky with two to three orders of magnitude more sensitivity than previous surveys, and will have an enormous field of view facil- itating semi-continuous monitoring of more than half of the entire sky at the lowest frequencies. The Dutch LOFAR will be located entirely within a region of 200 km diameter in the north of ∼ the Netherlands. It will be composed of between 36 and 50 stations (depending upon finances), approximately half of which will be located in a 2 km core close to Exloo. Each