Transcript “The” Square Kilometer Array and the Future of Radio Astronomy

“The” Square Kilometer Array
and the Future of Radio Astronomy
Alyssa Goodman
Harvard-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
Today’s SKA Discussion
Science
Engineering
Politics
Engineering Science Politics
Today’s SKA Discussion
Science
Engineering
Politics
Engineering 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-a 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 + n/5) GHz
Instrument Aeff/Tsys
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 GHz
Angular Resolution: 0.1” @ 1.4 GHz
Image Dynamic Range: 106 @ 1.4 GHz
Spatial Pixels: 108
Number of Spectral Channels: 104
Instantaneous Pencil Beams: 100
70m
145
GBT
285
VLA
280
Arecibo 1,414
ALMA
98
ATA
193
DSNarr 3,547
SKA
20,000
“Wide Field” Imaging
1º field of view at l=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-a 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 & Tradeoffs
Few
$
Small
Nelements
Many
Cost/Element
$$$$$
Field of View
(Primary Beam)
Large
Bandwidth vs. Nbeams
Realizations
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Science & “Compliance”
Number of Galaxies
H I in (Distant) Galaxies
Volume (cubic Mpc)
Z=3.6
Redshifted CO
25 GHz
Z=4
“Epoch of Reionization”
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Movie courtesy N. Gne
RFI
ANNOYANCES
22 GHz
150 MHz
Interference Suppression & Excision Are
Essential
= “Radioastronomy” Bands
Another Annoyance: A Confusion
Limit!
Hubble Deep Field
VLA
50 hours at 8.7 GHz gives
6 sources at >12 mJy
images courtesy R. Ekers
Simulated SKA
1 mJy sensitivity
at 1.4 GHz
(and this is just a tiny piece
of full field of view)
Today’s SKA Discussion
Science
Engineering
Politics
Engineering 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: LAR
Large Adaptive Reflectors
Legg 1998, A&AS, 130, 369
www.drao.nrc.ca/science/ska/#documents
Clip
Secondary held
aloft by derigable
Large-N Designs
Processor
Lenses and Flats
Sub-arrays of lenses or planes phased
and combined to form a larger array
Large 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
Large N-Small-D Cost, in 2010
SKA Cost Breakdown by Subsystem vs Antenna Diameter
Aeff/Tsys = 20,000, Aeff=360,000, Tsys=18K, BW=4GHz, 15K Cryogenics
Antenna Cost = 0.1D^3 K$, 2010Electronics Cost = $15K per Element
2,000,000
Fixed Costs
Civil Station
Total Cost, $K
1,500,000
Signal Transmission
Central Processing
Electronics
Antenna
1,000,000
Antenna
500,000
Electronics
Signal Transmission
0
5
8
Central Processing
Fixed Costs
10
12
15
Antenna Diameter, Meters
Civil Station
20
30
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Science & “Compliance”
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
Science
Engineering
Politics
Engineering 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
* maybe
– SW Austalia and/or SW US likely choices
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(Inter)National SKA Politics
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When & How?
International SKA Steering Committee
(ISSC) will select a design in ~20052007
Funding: Multi-National
US Share:
NSF +
Possible collaboration with NASA/DSN?
Today’s SKA Discussion
Science
Engineering
Politics
Engineering 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
Cassini
VIMS
Instrumental
Data Rates at
Saturn
(bits/sec)
Multi-Spectral & Hyper-Spectral Imagers
Planetary Images
104
105
106
107
108
Video
Internet Connection
HDTV
(T-1 Line)
Current Capability
(at 8.4 GHz)
SKA Capability
(at 32 GHz)
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 Politics
A 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 (costD2.7)
• Larger N means more receivers, more fiber,
and bigger correlator
• Larger N allows for more baselines, better uv coverage
• Small dishes give big primary field of view
(but observation/calibration may be more difficult at short l)
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