The Expanded Very Large Array

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					The Expanded Very Large Array:

    Pathfinder for the SKA

            Rick Perley
                       The EVLA Project
• The EVLA Project’s Goal is to multiply at least tenfold the
  capabilities of the VLA in all areas:
      –   Sensitivity
      –   Frequency Coverage
      –   Spectral Capabilities
      –   Imaging Quality
      –   Spatial Resolution
      –   User Access
•  The EVLA Project is leveraged upon the considerable
  existing infrastructure of the VLA.
• It is a very cost-effective project, particularly in terms of
  operations: > 10-fold improvement at 10% increment in
  operational cost.
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                    EVLA Specifications
• Milliarcsecond resolution, giving:
      – 5 AU resolution at Orion, 1 pc at Virgo cluster, 100 pc at z = 1.5.
• <100 nJy pnt-src. continuum sensitivity (1-s, 400h), giving:
      – ~2.5 K brightness temperature sensitivity on milli-arcsecond scales.
• Continuous baseline coverage from 35 m to 350 km.
      – Can image all spatial scales with > 109 pixels.
• Continuous frequency coverage from 1 to 50 GHz.
      – Provides up to 8 GHz bandwidth, full redshift coverage.
• A state-of-the-art correlator built by our Canadian partners
      – Full 16 GHz bandwidth, polarization, minimum 16384 channels.
      – Frequency resolution range from > 1 MHz to < 1 Hz.
      – Sub-banding capability to concentrate resources where needed.

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                The EVLA can meet these
                 Specifications – Now!
• The technologies to attain all these requirements are here
now. No lengthy technological development is needed.

•The 2000 AASC (‘Decadal Panel’) recognized the EVLA’s
crucial role for astronomy, and gave it its 2nd highest
recommendation amongst major ground-based new facilities.
      – History shows that all highly-ranked projects get built.

• The EVLA will be one of the ‘great observatories’ currently
under design or construction, and will provide unique
capabilities in resolution, sensitivity, and imaging capability.

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            What is NOT in the Specifications?
• No new capability below 1 GHz.
• It proves to be very difficult to implement a low-
  frequency capability on our existing 25-meter
• Various suggested approaches are too expensive,
  and/or are not tested.
• The low-frequency capability has been removed
  from the Phase II proposal.

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                `Astronomical Discovery Space’
                The Frequency-Resolution Plane

                                                     Coverage of various
                                            10 mas
                                           10 mas    future/current
                                                     instruments is shown.

                                                     Upper limit set by
                                                     diffraction, or

                                                     Lower limits set by
                                                     telescope or antenna
                                                     field of view.

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                Why do the EVLA?
• There is only one good answer:
                     For the Science!
• This audience knows well the unique capabilities of radio
  astronomy, its glorious history and valuable potential role
  for all of astronomy.
• But accessing this potential requires a state-of-the-art
  instrument, and the world’s premier radio telescope has
  had its basic capabilities frozen for over 20 years!
• Needed to maintain a healthy research community.
• An order-of-magnitude improvement in capability
  promises – and will deliver – a huge science payoff.

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                The Two Phases of the EVLA
    The EVLA Project is split into two phases:

• Phase I: Modernizing the existing facility.
      – Began in 2001, progress is very good.
      – Plan is to finish by 2012 – sooner if possible.

• Phase II: Extending the spatial resolution range.
      – Proposal was submitted to the NSF on April 15, 2004.
      – 7-year implementation plan.

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                Phase I Key Components
• Sensitivity Improvements
      – Factor of a few to 20 in continuum sensitivity by improving
        receivers and widening BW to 8 GHz/poln.
• Frequency Accessibility
      – Full frequency coverage from 1 to 50 GHz by adding two new
        bands (2—4 and 28—40 GHz).
• Spectral Capabilities
      – Modern digital correlator, with minimum 16284 channels, flexible
        sub-band tuning, full polarization, resolution from 1 MHz to 1 Hz.
• Operational Improvements through ‘e2e’ approach.
      – Proposal generation, telescope scheduling, archiving, automatic
        default image preparation, data access, data export, exportable
        processing software.
      – Renewed vigor in algorithmic improvements to give noise-limited
        imaging, in all Stokes’ parameters, throughout the primary beam.
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                Phase II Key Components
• Increase resolution tenfold by establishing the NMA.
      – 8 new `VLBA-style' antennas, each with eight frequency bands.
      – Upgrading two VLBA antennas (PT and LA) to EVLA standards.
      – Connection by existing, rented fiber to new correlator for full-
        bandwidth, real-time operations.
      – Operated with EVLA27, or as a stand-alone array, providing
        current VLA sensitivity with ten times the resolution.
• Incorporation of VLBA within EVLA
      – New correlator capable of simultaneously correlating real-time and
        disk-recorded data.
      – This correlator will replace both VLA and VLBA correlators.
      – VLBA and EVLA run as a single operational structure.
• Enhanced imaging capability for low-brightness structure.
      – 20 new stations, with max. baseline ~300 meters.
      – Defines a new `E’-configuration.
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                 EVLA Science Themes
• For Phase I, the science case built upon the unique
  capabilities of radio astronomy, and the benefits of
  increased sensitivity and frequency access – The
  Four Themes:
      –   Magnetic Universe
      –   Obscured Universe
      –   Transient Universe
      –   Evolving Universe
• For Phase II, the case is built upon the unique
  combination of resolution, sensitivity and
  imaging. The single Phase II Theme:
      – Resolution of Cosmic Evolution
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            Location of the NMA Antennas
                                   • The new antennas are
                                     shown in white.
                                   • Upgraded VLBA
                                     antennas are in
                                   • All sites are on public
                                     land, with road
                                     access, nearby power
                                     and fiber.
                                   • Fiber rental costs
                                     very modest
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                Phase I Status and Progress
• A proposal for $50M (2000 dollars) was submitted to the
  NSF in May 2000.
• Funding from the NSF began in 2001, at a rate of
  $5M/year, with completion anticipated by 2012.
• Canadian government approval for full correlator funding
  (US$14.4M) came in 2003.
• Prototype testing is well under way.
• ‘First Light’ occurred last October. ‘First Fringes’ were
  obtained in March.
• The test antenna (# 13!) should be available for normal
  observing by the end of the summer.
• Outfitting of other antennas to begin early 2005.
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                Phase II Status and Timescale
 • Phase II proposal, for $117M, submitted to NSF in
   April 2004.
 • Proposal is the Major Research Equipment (MRE)
   line – stiff competition from all NSF branches.
 • However, only one other astronomy MRE proposal
   has been submitted (Advanced Technology Solar
 • MRE proposals for LSST and TMT (= GSMT) not
   expected for many years – they are apparently not
   ready for construction.
 • Lengthy approval process expected.
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           The EVLA –> SKA Connection
• There are numerous technical challenges for the SKA
  which are common to the EVLA:
     – Cost-effective broadband data transmission
     – Data management for large correlators.
     – High dynamic range, noise-limited, full polarimetric imaging over
       large fields of view.
     – Spatially-variant gain calibration (antenna pointing variations,
       atmospheric and ionospheric screen).
     – Non-coplanar imaging, mosaicing.
     – Default image generation, image pipelining, data access and export
     – RFI avoidance, suppression, accommodation, and excision.
     – Exploration of the sub-mJy sky.
     – Management of an international project – this is a 3-country effort
       (USA, Canada, Mexico) which is working very well.
• The EVLA is an essential step towards an SKA!
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