“The” Square Kilometer Array and the Future of Radio Astronomy Alyssa Goodman Harvard-Smithsonian Center for Astrophysics

“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


ScienceEngineering


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”

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

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


ScienceEngineering


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”


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


ScienceEngineering


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




When & How?

International SKA Steering Committee (ISSC) will select a design in ~2005-2007

Funding: Multi-NationalUS Share:

NSF +Possible collaboration with NASA/DSN?


ScienceEngineering


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

Documents

“The” Square Kilometer Array and the Future of Radio Astronomy Alyssa Goodman Harvard-Smithsonian Center for Astrophysics