1 / 62

Astronomy, Radio Sources and Society

Astronomy, Radio Sources and Society. Extragalactic radio s ources and their importance for astronomy Leiden 10-13 June 2013 Ron Ekers CSIRO, Australia. George Miley.

ossie
Download Presentation

Astronomy, Radio Sources and Society

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Astronomy, Radio Sources and Society Extragalactic radio sources and their importance for astronomy Leiden 10-13 June 2013 Ron Ekers CSIRO, Australia

  2. George Miley The largest, the furthest, the most powerful, and to some of us the most fascinating objects known in the Universe are to be found among the radio sources associated with some elliptical galaxies and QSO’s. In recent years it has become apparent that they are also objects of considerable beauty. Ann. Rev. Astron. Astrophys, 1980

  3. 50th Anniversary of the Discovery of Quasars Mt Palomar 200” AAS Long Beach

  4. Geese Hoyle, Burbidge and Narlikar

  5. Linear size distribution of radio galaxies • 3CR radiogalaxies • Linear plot with linear bins ↕ • Log plot with log bins Ekers & Miley 1977

  6. The Scientific Method • Developed during the 17th century • Develop an hypothesis • Make predictions • Verify with observations (or discard hypothesis) • Eg Newton's theory of gravity • at the time Newton died it was still merely a hypothesis • It explained everything from planets to falling apples • It was verified by the return of Halley’s comet in 1758 • Since than it made many predictions Halley Lecture

  7. Astronomy • Most astronomy papers today are explanations of observed phenomena. • Predictions usually fail and it is considered normal practice to adapt the theory to fit the observations. • These theories may not be wrong, but without predictions we have no reason to accept them • Many examples in our interpretation of radio galaxies • The role of the scepticin science

  8. Where we are going from here • Some of the enabling technology • Martin Rees and the Wireless Internet • Radio Galaxies from the beginning • QSO 50th anniversary Blackholes • Some Extragalactic Radio Source Highlights • Galaxy formation and the early Universe

  9. Cambridge One-Mile Telescope: 1962

  10. June 1961 North pole survey 4C aerials 178 MHz Computations and graphical display used EDSACII 7 years after Christiansen First Cambridge Earth Rotation Synthesis Image

  11. Benelux Cross1963 • Joint Netherlands – Belgium • OEEC (now OECD) agreement • Christiansen et al design • 100x 30m + 1x 70m dish • 21cm • 1.5km

  12. Science Goals for Benelux Cross • Oort - OECD Symposium (1961) • Primary goal • Enough sensitivity and resolving power to study the early universe through source counts

  13. Westerbork: 1970 • Hogbom (Cambridge) + • Christiansen (Sydney) Benelux cross WSRT • 12 x 25m dishes • Two moveable • 10 redundant spacings • Self calibration • Add 2 more 25m dishes later

  14. LOFAR: The Low Frequency Array • Oort Workshop 1997 • George Miley proposal to ASTRON • Arnold van Ardenne already thinking about SKA-low and the aperture arrays • Actively promoted by George • Low Frequencies are Cheap!

  15. LOFAR WILL EXPLORE NEW PARAMETER SPACE George Miley Tasmania 2008 • Lowest Radio Frequencies (< 50 MHz) (Wavelengths > 3 metre) • Neglected cradle of radio astronomy • Bill Erickson – a hero • Coherent radiation processes • Oldest synchrotron electrons – “Fossil” • Absorption • Huge Simultaneous Fields (tens of degrees with large-sky monitor triggering) • Searches for rare variable and transient sources and cosmic air showers • “Synoptic” telescope • High Dynamic Range Radio Spectroscopy at 110 – 230 MHz • Search for fingerprint of reionization • Neutral hydrogen (HI) at z ~ 11 to z ~7 DESIGN OF LOFAR DRIVEN BY FEW KEY PROJECTS

  16. From Cambridge to The Netherlands 1970then to Australia 1996 • Steven Hawking: black holes radiate • Small black holes evaporate in less than the age of the Universe • Martin Rees: a radio pulse might be observable when they disappear • John O’Sullivan: and collaborators build a special instrument to look for the exploding black holes using Dwingeloo and Westerbork • “there has to be a better way!” • Fourier Transform on a chip •  IEEE 802.11 wireless internet standard Ekers, Radio Sources & Society

  17. Cygnus Astrongest radio source in sky • Hey 1946 • source with variable intensity • time scale of seconds to minutes • must be small diameter • the first “radio star” • What was it? • no optical counterpart • was the whole galactic plane was made of such stars? • no theory linking diffuse galactic emission to cosmic rays

  18. What is the Non-thermal Radio Emission? • A very confusing story • Misinterpretation of radio data added to the confusion • some radio sources had small diameter (Hey). • Hey was correct but it was incorrectly assumed that all radio emission was the sum of these radio stars • It was assumed that the radio stars were like the sun • this was also incorrect. • they were galactic nebula (SNR) and extra galactic (AGN)

  19. Dover Heights, Sydney, Australia Piha and Leigh, New Zealand Cliff Interferometer 1948 • Cliff interferometer CSIRO, Australia - NZ (1948) • Built to identify the radio stars (John Bolton) • Identification of the Crab Nebula super novae remnant • Discovery of extragalactic radio sources at great distances • CentaurusA – NGC5128 and Virgo A – M87

  20. NGC5128

  21. Centaurus A

  22. Centaurus AATCA MosaicFeain et al 2011

  23. The First Radio Galaxies • 1949 : The first radio galaxies? “Positions of Three Discrete Sources of Galactic Radio-Frequency Radiation” - (Bolton, Stanley, and Slee, Nature 164, 101) • NGC 5128 and NGC 4486 (M87) have not been resolved into stars, so there is little direct evidence that they are true galaxies. If the identification of the radio sources are accepted, it would indicate that they are within our own Galaxy. Kellermann AAS Long Beach

  24. Why was it so difficult to accept extra-galactic? • Letter from Bolton to Minkowski 20 May 1949 • There were no galaxy experts at CSIR and very few in Australia • It was easier to assume that the strange galaxies were unusual galactic objects • There were no known mechanisms to explain the powerful radio emission if extragalactic

  25. Synchrotron Model for Radio Emission • 1949 Unsold: sunspots anomalous radiation • non-thermal • plasma oscillations • 1950 Alven & Herlofson: • synchrotron radiation from sunspots • 1950 Kiepenhauer (visiting Yerkes) • proposed the ISM rather than stars • needed magnetic field and high energy charged particles • He knew there was evidence for both • optical polarization and cosmic rays • Mostly ignored in the West but enthusiastically embraced in Russia by Ginzburg and later by Shklovski

  26. 3C 48, the first radio star • Small diameter source catalogue from Manchester • Henry Palmer & George Miley ? • Accurate position measured at OVRO • 1960 Tom Matthews and John Bolton identify 3C 48 with a stellar object • Greenstein, Munch, Sandage 200” spectra • Lots of unidentified spectral lines • Alan Sandage AAS paper (Dec 29, 1960), • Remote possibility that it may be a distant galaxy of stars. But there is general agreement … that it is a relatively nearby star. S&T, 21, l48 Adapted from Kellermann AAS Long Beach

  27. 3C 273 identification Cyril Hazard Parkes lunar occultation Kellermann AAS Long Beach

  28. 50th Anniversary of the Discovery of Quasars Mt Palomar 200” AAS Long Beach

  29. Striking difference in radio spectra Component A S = -0.9 Component B S = 0.0 Core – Jet morphology 3C273 Parkes Occultation 1962 Slide prepared by Jan Oort

  30. 3C273VLA 5GHz 1998

  31. 3C273Optical HST

  32. First Texas Symposium onRelativistic Astrophysics • Gravitational Collapse and Relativistic Astrophysics • Dallas, Texas, Dec 16-18 1963 • only gravity of a massive object in the nucleus of a galaxy could provide the energy • Fred Hoyle: • relativists with their sophisticated work were not only magnificent cultural ornaments but might actually be useful to science! • The University of Chicago Press, 1965

  33. The Nuclei of Galaxies • 1943: Carl Seyfert (Clevland, Ohio) • “Enhanced activity in the nuclei of 6 extragalactic nebulae • No citations for 18 years! • 1958: Viktor Ambartsumian (Armenia) • Championed the role of the galaxy nuclei • 1961: Vitaly Ginzburg (Russia) • Showed that gravitational energy could power a radio galaxy

  34. The Energy Source • Old models disappear fairly quickly • Galaxies in collision (Baade & Minkowski)  Bad theory • Nuclear energy • Electromagnetic flares • Redshift controversy lasts for many years • Many argued that the quasars are nearby  Bad theory • New physics was better than the incredible luminosity • But all predictions failed • Gravitational energy from a collapsed object • Ginzburg, Hoyle, Fowler, Zeldovich, Novikov..... • This was a paradigm shift • But what kind of condensed object?

  35. Black Holes • Chandrasekhar (1931) – paper rejected by ApJ • “A star of large mass cannot pass into the white dwarf stage, one is left speculating on other possibilities” • Eddington – the authority • “a star would have to go on radiating and radiating, and contracting and contracting….I think there should be a law of nature to stop matter behaving in this absurd way” • Oppenheimer (1939) – exercise in abstraction • “the star closes itself off from any communication…only its gravitational field persists”

  36. NGC326 – pressing jetBinary Black hole? • Martin Rees 1978 • One black hole already pushes credibility – two was a step too far

  37. VLA 1.4GHz NGC326 – pressing jetBinary Black Hole? • Martin Rees 1978 • One black hole already pushes credibility – two was a step too far • Binary Black holes? • Evidence for super massive binary black hole mergers and Gravitational wave predictions Murgia et al, A&A 380, 102-116 (2001) Merritt & Ekers Science (2002)

  38. Suspected SMBH binaries • 3C75-type sources: wide binaries

  39. PKS0637-752 – Quasar with Xray/radio jet Periodic outbursts interpreting Pks0637-752 • Binary black-hole in bound orbit • periodiclyplunges through the accretion disk • will maintain its spin axis so gets a new accretion disk each plunge

  40. Hercules A VLA and HST Baum et al (2012)

  41. NGC1265 head tail radio source • Head tail radio source • Rosetta stone for radio galaxies • Provided the time stamp • Radio source aging model was incorrect • Fixed by re-acceleration

  42. Fornax A on optical image

  43. Fornax A Depolarization

  44. Fornax A and the ant like feature • Need a turbulant magneto-ionic medium • RM > 20 rad m-2 • Size 14” • Eg • Ne = .03 cm-3 • B = 2 μG • L = 100pc • M = 109 Mo • Bland-Hawthorne ApJ 447, L77 (1995) • Halpha detection at v = 1610km/s Ron Ekers

  45. NGC6251Alignment • VLBI cores aligned to within a few degrees over scale changes of 5x106 • Hence maintains axis for at least 108 years

  46. 3C273 superluminal expansionpredicted & observed

  47. Relativistic outflow in AGNM87 • One sided  Doppler boost but components have v/c < 1 ! • components are slow moving shocks not measuring bulk flow • evidence for original interpretation is now lost!

  48. Centaurus A - closest AGN HIPASS 21cm Continuum Preliminary continuum image, courtesy Mark Calabretta (CSIRO ATNF)

  49. 600kpc Centaurus AATCA Mosaic • 1.4GHz continuum • full polarization • 4 x 750m array configuration • 406 pointings, hexagonal grid • FOV 45 deg2 • θ~45’’ • ~0.26mJy/beam (0.1K) • IlanaFeain

  50. Cen A Mosaic N lobe

More Related