The Square Kilometer Array

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The Square Kilometer Array -- The Radio
Telescope for the 21st Century
John M. Dickey
University of Minnesota School of Physics and
Astronomy 7 November 2001
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SKA Poster
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Talk Outline
How to build it

• radio telescope background
• SKA specifications
• design concepts

Why to build it

• cosmology
• Galactic astronomy
• pulsar astronomy

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Radio Telescope Sensitivity
Exponential increase in sensitivity x 105 since
1940 ! 3 year doubling time for sensitivity
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Radio Telescope Sensitivity
NAIC Arecibo Observatory 305m diameter
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Radio Telescope Sensitivity
NRAO Very Large Array 27 _at_ 25m diameter
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Radio Telescope Sensitivity
October 2001 the NRAO Green Bank Telescope
(GBT)
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Radio Telescope Sensitivity
One concept for the Square Kilometer Array (SKA)
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Square Kilometer Array The Idea

• Frequency range 0.03 - 20GHz
• Sensitivity 100 x VLA
• Resolution 0.1 0.001
• Multibeam (at lower frequencies)
• Need innovative design to reduce cost
• International funding unlikely to exceed 1000m
• 106 sq metre gt 1000 / sq metre
• cf VLA 10,000 / sq metre (50GHz)
• GMRT 1,000 / sq metre (1GHz)
• ATA 2,000/sq metre (11GHz)

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Strawman specifications

• Aeff/Tsys 2 x 104 m2/K
• Sky coverage 2 sterad
• Frequency range 0.03 - 20 GHz
• Imaging Field of View 1 square deg. _at_ 1.4 GHz
• Number of instantaneous pencil beams 100
• Maximum primary beam separation
• low frequency 100 deg
• high frequency 1 deg _at_ 1.4 GHz
• Number of pixels 108
• Angular resolution 0.1 arcsec _at_ 1.4 GHz
• Surface brightness 1K _at_ 0.1 arcsec (continuum)
• Instantaneous bandwidth 0.5 f/5 GHz
• Number of spectral channels 104
• Number of widely spaced, simultaneous frequency
  bands 2
• Clean beam dynamic range 106 _at_ 1.4 GHz
• Calibratible polarisation purity -40 dB

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SKA Continuum Sensitivity
HST
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SKA Spectral Line Sensitivityexample M101 at z
2
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Redshift Surveys
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SKAs 1o field-of-view

• for surveys and transient events in 106 galaxies !

SKA 20 cm
15 Mpc at z 2
ALMA
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Multi beams
Element antenna pattern
Station antenna patterns
Synthesized beams
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• Observing teams with their own beams
• like particle accelerator, but can have all beams
  simultaneously
• Baseband buffer
• Observe before trigger !

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NFRA 1998
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SKA Poster
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Phased Array
Alternate idea replace mechanical pointing, beam
forming by electronic means
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SKA Cost v Dish Size 2001
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Mass-produced parabolas The Allen Telescope
Array

• UCB, SETI Institute
• 100m equivalent
• 350 x6.1 m parabolas
• 0.5-11 GHz (simultaneously)
• Complete 2005

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Some new antenna concepts
China KARST Canadian aerostat US Large
N Australian Luneburg Lenses Dutch phased array
Design Choice in 2005
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China

• Karst region for array of large Arecibo-like
  Telescopes
• D gt 200 m

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Aerostat Paraboloid
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Australian Concept An array of
Luneburg lenses, each with multiple receivers.
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Luneburg Lens

• Spherical lens with variable permittivity,
  er (2 r2)

• A collimated beam is focussed onto the other side
  of the sphere

• Beam can come from any direction

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One configuration concept for science goals
Not a single 1 km square aperture !
a wide range of baselines
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The Dutch concept A tiled aperture made
up of array receivers.
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Talk Outline
How to build it

• radio telescope background
• SKA specifications
• design concepts

Why to build it

• cosmology
• Galactic astronomy
• pulsar astronomy

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• A few of the scientific goals of the SKA
• cosmology - the epoch of reionization
• galaxy formation and interaction
• Milky Way structure and dynamics
• stars, star formation, and star death
• solar and planetary physics

http//www.ras.ucalgary.ca/SKA/science/science.htm
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• A few of the scientific goals of the SKA
• cosmology - the epoch of reionization
• galaxy formation and interaction
• Milky Way structure and dynamics
• stars, star formation, and star death
• solar and planetary physics

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The Cosmic Web
Spectra of QSOs show many Ly-a absorption
lines due to low column density H N-body
simulations predict the existence of a
cosmic web Complicated structure of filaments
and sheets of material SKA will detect this
web In HI emission!
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The HI line may be detectable from the epoch of
reionization, and before, in either emission or
absorption, depending on the history of
the radiation field at the Lyman alpha frequency
...
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Somewhere 15 gt (1z) gt 6
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The SKA will have the sensitivity and resolution
to easily detect the pre-reionization gas...
... if we can solve the problem of confusion by
interference and Galactic foregrounds.
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Stepping foreward to the present day ..
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A Universe of Stars
A Universe of Hydrogen gas
Yun, Ho, and Lo, 1994
M81 group
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Galactic Magnetic Field Measurements

• Zeeman splitting of emission and
• absorption lines of HI and molecular
• lines.

• Faraday rotation of linearly polarized
• synchrotron emission.

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Heiles (1988) 21-cm Zeeman splitting study of
B in L204.
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magnetic field B 3 mG
noise level 5 mK in 0.5 km/s channels integration
time 10 h
Brightness sensitivity is critical !
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starlight polarization

CO mapping

Zeeman splitting
Does this cloud trace a magnetic flux tube ?
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Modelling the Galactic magnetic field to fit the
observed Rotation Measures.
With the SKA we will measure RMs toward
extragalactic sources with polarized flux at
the microJy level. There are hundreds of these
per degree of longitude with b lt 1o.
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High resolution Galactic HI surveys With the
SKA we can do what we do today with 50 times
higher resolution.
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Parkes
Compact Array
see McClure-Griffiths et al. 2000 and
Stanimirovic 1999
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Pulsars and their uses .
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Pulsars
Born in the Galactic plane and then move away
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Pulsar Surveys
Current Surveys will discover 1000 pulsars

• 100,000 potential observable pulsars
• gt10,000 new pulsars expected with SKA
• Probably 1,000 millisecond pulsars

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SKA pulsar survey
10,000 pulsars throughout Milky Way
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Unique Laboratories for General Relativity
e.g. timing of B191316
Orbit shrinks every day by 1cm! Confirmation of
gravitational waves!
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Cosmological Gravitational Wave Background
Timing a net of millisecond pulsars
Look for spatial pattern in timing residuals!
Pulsarsarms of huge gravitational wave detector
Timing precision of 100 nanoseconds needed ? SKA
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The International Square Kilometer Array Steering
Committee Science Working Group
United States Canada Netherlands Great
Britain India China Australia
Memorandum of Understanding August 2000
http//www.ras.ucalgary.ca/SKA/science/science.htm
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ISSC Timeline
-- 2005 Proof of Concepts 2005 Design
and Site Choice 2006 - 2009 Design Study
prototypes 2010 - 2015
Construction 2015 -- Operation
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The United States Square Kilometer
Array Consortium
Univ. of California at Berkeley Caltech - JPL MIT
- Haystack Observatory Harvard Cornell -
NAIC Univ. of Minnesota Ohio State
Univ. NRAO NRL SETI Institute
http//www.usska.org/
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SGPS web site
http//www.astro.umn.edu/naomi/sgps.html
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Radio Telescope Sensitivity
SETI Institute / U C Berkeley Allen Telescope
Array (ATA) formerly the 1 hectare telescope
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SGPS web site
http//www.astro.umn.edu/naomi/sgps.html