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

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

2. 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

3. Today’s SKA Discussion Science Engineering Politics Engineering Science Politics

4. Today’s SKA Discussion Science Engineering Politics Engineering Science Politics

5. 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

6. Strawman SKA Specifications Frequency Range: 150 MHz - 20 GHz Instantaneous Bandwidth : (0.5 + n/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 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 InstrumentAeff/Tsys 70m 145 GBT 285 VLA 280 Arecibo 1,414 ALMA 98 ATA 193 DSNarr 3,547 SKA 20,000

7. “Wide Field” Imaging 1º field of view at l=20cm with 0.1" resolution

8. 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

9. Decisions & Tradeoffs

10. Realizations

11. Science & “Compliance”

12. H I in (Distant) Galaxies Number of Galaxies Volume (cubic Mpc)

13. Highly redshifted CO Z=3.6 Redshifted CO 25 GHz Z=4

14. “Epoch of Reionization” LOFAR... Movie courtesy N. Gnedin

15. RFI ANNOYANCES

16. Interference Suppression & Excision Are Essential 150 MHz 22 GHz = “Radioastronomy” Bands

17. Another Annoyance: A Confusion Limit! Hubble Deep Field VLA Simulated SKA 1 mJy sensitivity at 1.4 GHz (and this is just a tiny piece of full field of view) 50 hours at 8.7 GHz gives 6 sources at >12 mJy images courtesy R. Ekers

18. Today’s SKA Discussion Science Engineering Politics Engineering Science Politics

19. Engineering Designs

20. 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

21. Small N: LAR Large Adaptive Reflectors Legg 1998, A&AS, 130, 369 www.drao.nrc.ca/science/ska/#documents Secondary held aloft by derigable

22. Large-N Designs Processor

23. 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

24. 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

25. 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

26. Large N-Small-D Cost, in 2010

27. Science & “Compliance”

28. 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

29. Today’s SKA Discussion Science Engineering Politics Engineering Science Politics

30. 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

31. (Inter)National SKA Politics

32. When & How? International SKA Steering Committee (ISSC) will select a design in ~2005-2007 Funding: Multi-National US Share: NSF + Possible collaboration with NASA/DSN?

33. Today’s SKA Discussion Science Engineering Politics Engineering Science Politics

34. 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

35. 104 105 106 107 108 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 Multi-Spectral & Hyper-Spectral Imagers Instrumental Data Rates at Saturn (bits/sec) Planetary Images Video HDTV Internet Connection (T-1 Line) Current Capability (at 8.4 GHz) SKA Capability (at 32 GHz)

36. 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

37. 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.

38. Engineering Science PoliticsA Hybrid Array Processor

39. Discussion: The CfA and the SKA

40. 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 u-v coverage • Small dishes give big primary field of view (but observation/calibration may be more difficult at short l)

41. 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