“The” Square Kilometer Array and the Future of Radio Astronomy Alyssa Goodman Harvard-Smithsonian Center for Astrophysics QuickTime™ and aTIFF (LZW) decompress
Jan 15, 2016
“The” Square Kilometer Array and the Future of Radio Astronomy
Alyssa GoodmanHarvard-Smithsonian Center for Astrophysics
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United States Square Kilometer Array Consortium (USSKA)
Lincoln Greenhill and Alyssa Goodman are SAO and Harvard representatives
David Wilner and Bryan Gaensler are on the International Science Working Group
Other institutions in the USSKA: Cornell/NAIC, MIT/Haystack, Caltech/JPL, U.C. Berkeley, U. Mn., OSU, NRAO, SETI Institute, NRL
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Today’s SKA Discussion
ScienceEngineering
PoliticsEngineering Science Politics
Today’s SKA Discussion
ScienceEngineering
PoliticsEngineering Science Politics
Formation and Evolution of Galaxies • The Dawn of Galaxies: Searching for the Epoch of First Light • 21-cm Emission and Absorption Mechanisms • Preheating the IGM • SKA Imaging of Cosmological HI • Large
Scale Structure and Galaxy Evolution • A Deep SKA HI Pencil Beam Survey • Large scale structure studies from a shallow, wide area survey • The Ly- forest seen in the 21-cm HI line • High Redshift CO • Deep Continuum Fields • Extragalactic Radio Sources • The SubmicroJansky Sky • Probing Dark Matter with
Gravitational Lensing • Activity in Galactic Nuclei • The SKA and Active Galactic Nuclei • Sensitivity of the SKA in VLBI Arrays • Circum-nuclear MegaMasers • H2O megamasers • OH Megamasers • Formaldehyde
Megamasers • The Starburst Phenomenon • Interstellar Processes • HII Regions: High Resolution Imaging of Thermal Emission • Centimetre Wavelength Molecular Probes of the ISM • Supernova
Remnants • The Origin of Cosmic Rays • Interstellar Plasma Turbulence • Recombination Lines • Magnetic Fields • Rotation Measure Synthesis • Polarization Studies of the Interstellar Medium in the Galaxy and in Nearby External Galaxies • Formation and Evolution of Stars • Continuum Radio Emission from Stars •
Imaging the Surfaces of Stars • Red Giants and Supergiant Stars • Star Formation • Protostellar Cores • Protostellar Jets • Uncovering the Evolutionary Sequence • Magnetic Fields in Protostellar Objects • Cool Star Astronomy • The Radio Sun • Observing Solar Analogs at Radio Wavelengths • Where are the many other Radio Suns? • Flares and Microflares • X-ray Binaries • Relativistic Electrons from X-ray Transients • The Faint Persistent Population • Imaging of Circumstellar Phenomena • Stellar Astrometry • Supernovae • Radio Supernovae • The Radio After-Glows of Gamma-ray Bursts • Pulsars • Pulsar Searches • Pulsar
Timing• Radio Pulsar Timing and General Relativity • Solar System Science • Thermal Emission from Small Solar System Bodies • Asteroids • Planetary Satellites • Kuiper Belt Objects • Radar Imaging of Near Earth
Asteroids • The Atmosphere and Magnetosphere of Jupiter • Comet Studies • Solar Radar • Coronal Scattering • Formation and Evolution of Life • Detection of Extrasolar Planets • Pre-Biotic Interstellar
Chemistry • The Search for Extraterrestrial Intelligence
SKA Science
Strawman SKA Specifications
Frequency Range: 150 MHz - 20 GHz Instantaneous Bandwidth : (0.5 + /5) GHz
Sensitivity (Aeff /Tsys): 2 x 104 m2 K-1
Surface Brightness Sensitivity:1 K @ 0.1” (continuum)
Polarization Purity: -40 dB
Imaging Field Of View: 1º @ 1.4 GHzAngular Resolution: 0.1” @ 1.4 GHzImage Dynamic Range: 106 @ 1.4 GHz
Spatial Pixels: 108
Number of Spectral Channels: 104 Instantaneous Pencil Beams: 100
Instrument Aeff/Tsys
70m 145GBT 285VLA 280Arecibo 1,414ALMA 98ATA 193DSNarr 3,547SKA 20,000
“Wide Field” Imaging
1º field of view at 20cm with 0.1" resolution
Formation and Evolution of Galaxies • The Dawn of Galaxies: Searching for the Epoch of First Light • 21-cm Emission and Absorption Mechanisms • Preheating the IGM • SKA Imaging of Cosmological HI • Large
Scale Structure and Galaxy Evolution • A Deep SKA HI Pencil Beam Survey • Large scale structure studies from a shallow, wide area survey • The Ly- forest seen in the 21-cm HI line • High Redshift CO • Deep Continuum Fields • Extragalactic Radio Sources • The SubmicroJansky Sky • Probing Dark Matter with
Gravitational Lensing • Activity in Galactic Nuclei • The SKA and Active Galactic Nuclei • Sensitivity of the SKA in VLBI Arrays • Circum-nuclear MegaMasers • H2O megamasers • OH Megamasers • Formaldehyde
Megamasers • The Starburst Phenomenon • Interstellar Processes • HII Regions: High Resolution Imaging of Thermal Emission • Centimetre Wavelength Molecular Probes of the ISM • Supernova
Remnants • The Origin of Cosmic Rays • Interstellar Plasma Turbulence • Recombination Lines • Magnetic Fields • Rotation Measure Synthesis • Polarization Studies of the Interstellar Medium in the Galaxy and in Nearby External Galaxies • Formation and Evolution of Stars • Continuum Radio Emission from Stars •
Imaging the Surfaces of Stars • Red Giants and Supergiant Stars • Star Formation • Protostellar Cores • Protostellar Jets • Uncovering the Evolutionary Sequence • Magnetic Fields in Protostellar Objects • Cool Star Astronomy • The Radio Sun • Observing Solar Analogs at Radio Wavelengths • Where are the many other Radio Suns? • Flares and Microflares • X-ray Binaries • Relativistic Electrons from X-ray Transients • The Faint Persistent Population • Imaging of Circumstellar Phenomena • Stellar Astrometry • Supernovae • Radio Supernovae • The Radio After-Glows of Gamma-ray Bursts • Pulsars • Pulsar Searches • Pulsar
Timing• Radio Pulsar Timing and General Relativity • Solar System Science • Thermal Emission from Small Solar System Bodies • Asteroids • Planetary Satellites • Kuiper Belt Objects • Radar Imaging of Near Earth
Asteroids • The Atmosphere and Magnetosphere of Jupiter • Comet Studies • Solar Radar • Coronal Scattering • Formation and Evolution of Life • Detection of Extrasolar Planets • Pre-Biotic Interstellar
Chemistry • The Search for Extraterrestrial Intelligence
Decisions & TradeoffsFew Nelements Many
$ Cost/Element $$$$$
Small Field of View (Primary Beam)
Large
Bandwidth vs. Nbeams
Realizations
Science & “Compliance”
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H I in (Distant) Galaxies
Volume (cubic Mpc)
Num
ber
of G
alax
ies
Redshifted CO
Highly redshifte
d CO
Z=
3.6
25 GHz
Z=4
“Epoch of Reionization”
Movie courtesy N. Gnedin
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RFI
ANNOYANCES
Interference Suppression & Excision Are Essential
= “Radioastronomy” Bands
150
MH
z
22 G
Hz
VLAHubble Deep Field Simulated SKA
Another Annoyance: A Confusion Limit!
50 hours at 8.7 GHz gives6 sources at >12 Jy
1 Jy sensitivity at 1.4 GHz
(and this is just a tiny pieceof full field of view)
images courtesy R. Ekers
Today’s SKA Discussion
ScienceEngineering
PoliticsEngineering Science Politics
Engineering Designs
Small N: KARST
An array of Arecibo-like, antennas to be located in southern China.
A potentially mammoth civil and mechanical engineering effort.
n.b. moving platform
Small N: LARLarge Adaptive Reflectors
Legg 1998, A&AS, 130, 369www.drao.nrc.ca/science/ska/#documents
Clip
Secondary heldaloft by derigable
Large-N Designs
Processor
Lenses and Flats
Sub-arrays of lenses or planes phased and combined to form a larger arrayLarge field of view, multiple beams
Adaptive RFI nulling
US: “Large N-Small D”with Parabolic Dishes
• Small, fully steerable dishes• Savings through use of commercial
manufacturing techniques • Sub-arrays phased and combined...• Configuration is expandable & flexible
(Note: length of largest baseline is a matter of debate.)
• Multiple beams• Adaptive RFI nulling or excision
The Allen Telescope Array[1 HT = 1 hectare = 104 m2 = 0.01 km2]
• Joint SETI Institute/UC Berkeley/Paul Allen Project• Simultaneous SETI and Radio Astronomy, using
multiple synthesized beams• Array of ~commercial satellite dishes (e.g. 535 x 5-
m)• <1 GHz to 10 or 12 GHz
• 35 K system temperature (Aeff/Tsys=190)• RFI Excision• "High-resolution" configuration ~20 arcsec at 21 cm• Rapid Prototype Array (RPA) of 1 HT completed, 7 x
3.6-m, 10 miles northeast of Berkeley
SKA Cost Breakdown by Subsystem vs Antenna DiameterAeff/Tsys = 20,000, Aeff=360,000, Tsys=18K, BW=4GHz, 15K CryogenicsAntenna Cost = 0.1D^3 K$, 2010Electronics Cost = $15K per Element
Fixed CostsCivil Station
Signal Transmission Central Processing
Electronics
Antenna
0
500,000
1,000,000
1,500,000
2,000,000
5 8 10 12 15 20 30Antenna Diameter, Meters
Total Cost, $K
Fixed Costs Civil Station
Signal Transmission Central Processing
Electronics Antenna
Large N-Small-D Cost, in 2010
Science & “Compliance”
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Computational Issues• N(N-1)/2 = millions• N(N-1)/2 x number of channels = billions• >1 GHz bandwidth • Connectivity
– Dedicated fibers?– Next generation internet?– Wiring within correlator and signal processors
• Data Processing (Very important)– Calibration and imaging (103 x Y2K cutting edge)– Storage, mining
Today’s SKA Discussion
ScienceEngineering
PoliticsEngineering Science Politics
When and Where?
SKA could be at least partly on-line c.2015*
Site selection depends on– Low RFI levels (long-term over a large
area)– Visibility (e.g., GC and LMC/SMC)– Nearby infrastructure– Real estate– Possibility of low labor costs– SW Austalia and/or SW US likely choices
* maybe
(Inter)National SKA Politics
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When & How?
International SKA Steering Committee (ISSC) will select a design in ~2005-2007
Funding: Multi-NationalUS Share:
NSF +Possible collaboration with NASA/DSN?
Today’s SKA Discussion
ScienceEngineering
PoliticsEngineering Science Politics
Future Large Arrays• Allen Telescope Array (ATA)
– 350 antennas– Construction is funded, antennas procured– Prototype array is operational
• Expanded Very Large Array (EVLA)– Phase 1: upgrade correlator and signal transmission (underway)– Phase 2: 8 new antennas providing ten times the angular
resolution
• Atacama Large Millimeter Array (ALMA)– 80 millimeter-wave antennas– Development funded/under construction
• Low Frequency Array (LOFAR)– Mostly funded, Preliminary Design Review TODAY– Good for EOR– Large N, Cheap Elements
• Square Kilometer Array (SKA): Cost ~$1B– Recommended by the National Academy of Sciences– US SKA Consortium funded at low (<$1M/year) levels by NSF– Major decisions (concept definition, site selection) by 2005
Engineering Science Politics: Radio Arrays for Deep Space Communication
A Square Kilometer of DSN-Array would:Provide factor of 100-500 increase in data rates from planetary missions (e.g. video)Allow mini-spacecraft with current data rates Enable direct Earth communication with probes/balloons
Synthetic Aperture Radar
Video
HDTV
Planetary Images
104 105 106 107 108
Multi-Spectral & Hyper-Spectral ImagersCassiniVIMS
Instrumental Data Rates at
Saturn (bits/sec)
Current Capability(at 8.4 GHz)
SKA Capability (at 32 GHz)
Internet Connection(T-1 Line)
Principal Benefits of a DSN Array
• Flexible capability– Devote sub-arrays to various missions– Multi-beaming around one planet– Can communicate directly with probes if desired (w/o orbiter)
• Exquisite positional information (5 nrad accuracy)– New capabilities for control– Reduced mission risk
• Uses existing infrastructure– Internet backbone could connect much of the array– Satellite-dish manufacturers can make reflectors
• Soft-failure– Bad weather or instrument breakdown are local phenomena, not
fatal to an array• Complementarity with Radio Astronomy “SKA”
– Shared development costs– Shared use of time on (multiple) arrays
The ~Current State of Affairs
The ISAC has identified four issues that appear paramount to the review process at this time:
• high and low frequency limits, • multibeaming and response times, • configuration, and • field of view. There was general agreement within the scientific working groups that reasonable compromises can be reached on the issues of
configuration and field of view. The ISAC (like the EMT) recognized that full-sky multibeaming must come at the expense of the high frequencies. If it came to a trade between the two, the majority of the ISAC feels that
high frequencies would take priority over multibeaming, although the novelty and practicality of multibeaming remains very attractive.
Again like the EMT, the ISAC recommends the designers consider hybrid solutions which include multibeaming capabilities at low frequencies.
Engineering Science PoliticsA Hybrid Array
Processor
Discussion: The CfA and the SKA
How large is N?KEY PRINCIPLES• Same collecting area with many small
dishes cheaper than one large dish (costD2.7)
• Larger N means more receivers, more fiber, and bigger correlator
• Larger N allows for more baselines, better u-v coverage
• Small dishes give big primary field of view (but observation/calibration may be more difficult at short )
No Correlator if Moore is Wrong
• Capacity – >1000 stns – Spectral-lines– Multiple
beams– Sub-arrays
• Cost– $75 M in 2011– 1 GHz clock
• XF design• Not feasible
today