Transcript Astronomy, Radio Sources and Society

Astronomy,
Radio Sources and Society
Extragalactic radio sources and their
importance for astronomy
Leiden 10-13 June 2013
Ron Ekers
CSIRO, Australia
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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
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50th Anniversary of the Discovery of Quasars
January 7, 2013
AAS Long Beach
Mt Palomar3 200”
Geese
Hoyle, Burbidge and Narlikar
Linear size distribution
of radio galaxies
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a
b
3CR radiogalaxies
Linear plot with
linear bins
↕
Log plot with log
bins
Ekers & Miley 1977
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The Scientific Method
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Developed during the 17th century
– Develop an hypothesis
– Make predictions
– Verify with observations (or discard hypothesis)
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Eg Newton's theory of gravity
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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
23May2007
Halley Lecture
Astronomy
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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 sceptic in science
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Where we are going from here
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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
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Cambridge One-Mile Telescope:
1962
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First Cambridge Earth
Rotation Synthesis Image
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June 1961
North pole survey
4C aerials
178 MHz
Computations and graphical
display used EDSACII
7 years after Christiansen
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Benelux Cross
1963
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Joint Netherlands – Belgium
OEEC (now OECD) agreement
Christiansen et al design
100x 30m + 1x 70m dish
21cm
1.5km
Science Goals for Benelux Cross
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Oort - OECD Symposium
(1961)
– Primary goal
» Enough sensitivity and resolving
power to study the early universe
through source counts
Westerbork: 1970
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Hogbom (Cambridge)
+
Christiansen (Sydney)
Benelux cross WSRT
 12 x 25m dishes
– Two moveable
– 10 redundant spacings
– Self calibration
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Add 2 more 25m
dishes later
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LOFAR: The Low Frequency
Array
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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!
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LOFAR WILL EXPLORE NEW PARAMETER SPACE
•
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
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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
From Cambridge to The Netherlands 1970
then to Australia 1996
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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!”
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Fourier Transform on a chip
–  IEEE 802.11 wireless internet standard
June 2013
Ekers, Radio Sources & Society
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Cygnus A
strongest radio source in sky
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Hey 1946
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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
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What is the Non-thermal Radio
Emission?
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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)
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Cliff Interferometer 1948
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Dover Heights, Sydney, Australia
Piha and Leigh, New Zealand
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
Centaurus A – NGC5128 and Virgo A – M87
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NGC5128
Centaurus A
Centaurus A
ATCA Mosaic
Feain et al 2011
The First Radio Galaxies
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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.
January 7, 2013
Kellermann AAS Long Beach
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Why was it so difficult to accept
extra-galactic?
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Letter from Bolton to Minkowski 20 May 1949
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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
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Synchrotron Model for Radio
Emission
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1949 Unsold: sunspots anomalous radiation
– non-thermal
– plasma oscillations
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1950 Alven & Herlofson:
– synchrotron radiation from sunspots
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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
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Mostly ignored in the West but enthusiastically
embraced in Russia by Ginzburg and later by Shklovski
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3C 48, the first radio star
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Small diameter source catalogue from
Manchester
– Henry Palmer & George Miley ?
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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
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January 7, 2013
Adapted from Kellermann AAS Long
3C 273 identification
Parkes lunar occultation
January 7, 2013
Kellermann AAS Long Beach
Cyril Hazard
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50th Anniversary of the Discovery
of Quasars
January 7, 2013
AAS Long Beach
28 200”
Mt Palomar
Slide prepared by Jan
Oort
3C273
Parkes Occultation 1962
 Striking difference
in radio spectra
 Component A
S = -0.9
 Component B
S = 0.0
 Core – Jet
morphology
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3C273
VLA 5GHz 1998
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3C273
Optical HST
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First Texas Symposium on
Relativistic Astrophysics
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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
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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
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The Nuclei of Galaxies
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1943: Carl Seyfert (Clevland, Ohio)
– “Enhanced activity in the nuclei of 6
extragalactic nebulae
– No citations for 18 years!
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1958: Viktor Ambartsumian (Armenia)
– Championed the role of the galaxy nuclei
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1961: Vitaly Ginzburg (Russia)
– Showed that gravitational energy could
power a radio galaxy
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The Energy Source
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Old models disappear fairly quickly
– Galaxies in collision (Baade & Minkowski)  Bad theory
– Nuclear energy
– Electromagnetic flares
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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
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Gravitational energy from a collapsed object
– Ginzburg, Hoyle, Fowler, Zeldovich, Novikov.....
– This was a paradigm shift
– But what kind of condensed object?
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Black Holes
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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”
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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”
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Oppenheimer (1939) – exercise in abstraction
– “the star closes itself off from any communication…only
its gravitational field persists”
NGC326 – pressing jet
Binary Black hole?
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Martin Rees 1978
– One black hole already
pushes credibility – two
was a step too far
NGC326 – pressing jet
Binary Black Hole?
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Martin Rees 1978
– One black hole already
pushes credibility – two
was a step too far
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Binary Black holes?
– Evidence for super massive
binary black hole mergers
and Gravitational wave
predictions
VLA 1.4GHz
Murgia et al, A&A 380, 102-116 (2001)
Merritt & Ekers Science (2002)
Suspected SMBH binaries
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3C75-type sources: wide binaries
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Periodic outbursts
interpreting Pks0637-752
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Binary black-hole in bound orbit
periodicly plunges through the accretion disk
– will maintain its spin axis so gets a new accretion disk
each plunge
PKS0637-752 – Quasar with Xray/radio jet
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Hercules A
VLA and HST
Baum et al (2012)
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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
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Fornax A
on optical image
Fornax A
Depolarization
Fornax A
and the ant like feature
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Need a turbulant magneto-ionic medium
RM > 20 rad m-2
Size 14”
Eg
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Ne = .03 cm-3
B = 2 μG
L = 100pc
M = 109 Mo
Bland-Hawthorne ApJ 447, L77 (1995)
– Halpha detection at v = 1610km/s
Nov 2010
Ron Ekers
NGC6251
Alignment
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VLBI cores aligned to
within a few degrees
over scale changes of
5x106
Hence maintains axis
for at least 108 years
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3C273 superluminal expansion
predicted & observed
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Relativistic outflow in AGN
M87
• 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!
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Centaurus A - closest AGN
HIPASS
21cm Continuum
Preliminary continuum image, courtesy Mark Calabretta (CSIRO
48 ATNF)
Centaurus A
ATCA Mosaic
1.4GHz
600kpc
continuum
 full polarization
4 x 750m array
configuration
406 pointings, hexagonal
grid
FOV 45 deg2
θ~45’’
 ~0.26mJy/beam (0.1K)
Ilana Feain
Cen A Mosaic N lobe
May 2012
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Centaurus A composite
May 2012
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Centaurus A middle lobe
X-ray XMM Newton
May 2012
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Centaurus A middle lobe
radio continuum and HI
Morganti
May 2012
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H alpha
Ellis and Bland-Hawthorne
May 2012
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LOFAR SCIENCE DRIVER 2: SURVEYS
2.1 ULTRA STEEP SPECTRUM SOURCES –
PROBE OF GALAXY AND CLUSTER FORMATION
e.g. Blumenthal & Miley 1988
e.g. Blumenthal & Miley 1988
Radio spectrum
Cygnus A
Larger redshifts > higher frequencies > steeper spectra
LOFAR WILL DETECT STEEPEST SPECTRA
(MOST DISTANT SOURCES)
The evolution of radio galaxies
BIG BANG
NOW
but USS spectra don’t steepen at all…
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our ATCA observations
confirm that high-z
radio galaxy spectra are
not curved
The K-correction interpretation is
inconsistent with observations
Klamer (Feien)
MNRAS (2006)
July 2005
Ilana Klamer - ASA
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Evolution of density fluctuations
ρ  (1+z)3
ρ=0
Δρ
ρclus
ρ=0
z=6 27 Nov 1999
R D Ekers
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z=0
Radio Galaxy - 4C41.17
redshift 3.8
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Alignment of radio jets (contours)
with other tracers of star formation
– VLA radio image
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HST F702
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HST F569
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Ly-α
van Breugel (1985)
13 July 05
R D Ekers
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Alignment with Radio Axis
Radio PA
Dust PA CO PA
Predicted an alignment in 4C41.17
Observed Δpa = 8o
Klamer et al. 2004
13 July 2005
R D Ekers
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Survey of CO
in High z Radio Galaxies
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13 high redshift radio galaxies
– 1.4 < z < 2.8
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CO (1-0) aligned with radio axis!
Emonts, Miley et al 2013
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The power of science is its ability
to make predictions
but science itself will evolve in
unpredictable ways
March 2013
Ekers
Conclusion
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