dougherty_EVLA by dandanhuanghuang

VIEWS: 4 PAGES: 26

									                                   The EVLA Project

                                         Sean Dougherty
                                     National Research Council
                                 Herzberg Institute for Astrophysics

                             Rick Perley & Michael Rupen (NRAO)
                                     Peter Dewdney (HIA)




Sub-mm/mm Observing Techniques              The EVLA                   Aug 14, 2006
                      What is the Very Large Array (VLA)
                      What is the Very Large Array (VLA)?




27 “movable” antennas                                   Completed in 1980
25 m diameter each                                      Receivers @ 92,21,6,3.6,2,1.3,0.7cm
Total area = 130-m dish
                                                        100 MHz total bandwidth
Y configuration (“2D” array)

Longest baseline = 36 km

World’s ‘largest’ array.

  Sub-mm/mm Observing Techniques   The EVLA                                    Aug 14, 2006
Sub-mm/mm Observing Techniques      SMD – Basic Radio Astronomy                Aug 14, 2006
                         The VLA – the Scalable array
  Moveable Antennas              Railroad and “trains”




Sub-mm/mm Observing Techniques          The EVLA         Aug 14, 2006
                                 Why upgrade the VLA?
    •    The VLA is the world’s premier imaging radio telescope:
            – fast, sensitive, flexible, productive
    •    If it’s so good – what’s the problem?
    •    Astronomy today requires a more powerful and flexible radio telescope
         than the VLA.
            – more sensitivity
            – more frequency coverage
            – more spectral flexibility
            – better imaging….
    •    No significant technical upgrades since completion
            – 1970s technology severely limits scientific capability.
    •    Modern electronics and signal processing  vastly increase the VLA’s
         scientific capabilities.




Sub-mm/mm Observing Techniques               The EVLA                   Aug 14, 2006
               The EVLA Project – leveraging the VLA

  •    Builds on the existing infrastructure
         – antennas, array, railroad, people

  •    Implement new technologies
         –   Receivers
         –   Electronics
         –   Data transmission
         –   Correlator

  •    Goal of ten Times the “astronomical capability” of the VLA

         – Sensitivity, Frequency coverage, Image Fidelity, Spectral Capabilities

         – On a timescale and cost far less than required to design, build, and implement a
           new facility.




Sub-mm/mm Observing Techniques            The EVLA                                  Aug 14, 2006
          EVLA: order-of-magnitude improvements

                           Parameter                      VLA       EVLA            Factor

  Point Source Sensitivity (1-s, 12 hours)               10 mJy      1 mJy             10

  Maximum BW in each polarization                        0.1 GHz    8 GHz              80

  # of frequency channels at max. bandwidth                16       16,384            1024

  Maximum number of frequency channels                    512      4,194,304          8192

  Coarsest frequency resolution                          50 MHz     2 MHz              25

  Finest frequency resolution                            381 Hz     0.12 Hz           3180

  (Log) Frequency Coverage (1 – 50 GHz)                   22%       100%                5



              • The EVLA performance is vastly better than the VLA
              • EVLA cost is less than ¼ the VLA capital investment
              • No increase in basic operations cost

Sub-mm/mm Observing Techniques                The EVLA                         Aug 14, 2006
                        How is sensitivity improved?

                                                            Tsys    1
 • Recall minimum detectable flux:               s s  2k
                                                            Ae      
 • Reduce Tsys
       – Lower Trx - better receivers
       – Lower Tspill – new feed designs

                    Tsys
 • Increase Ae via antenna efficiency
       lcm VLA EVLA
 • Improves both continuum &
       20     60    26
   spectral line observations
             6        50         31
 • For continuum, increase 
       3.6 30      34
       – 100 MHz to 8 GHz
             2        116        39
             1.3      154        54
Sub-mm/mm Observing Techniques        The EVLA                            Aug 14, 2006
                                 Frequency Coverage

  •    Continuous frequency coverage
       from 1 to 50 GHz
         –    a key EVLA requirement
   match instrument to science, not
    science to instrument!




  Blue - current VLA Green - EVLA
  Yellow letters and bars show band names and
      boundaries.
  Two low frequency bands (74 and 327 MHz)
      omitted




Sub-mm/mm Observing Techniques             The EVLA   Aug 14, 2006
                          Point-Source Sensitivity
                        Improvements : 1-s, 12-hours




                        Red: Current VLA          Black: EVLA Goals
Sub-mm/mm Observing Techniques         The EVLA                       Aug 14, 2006
           Bandwidth, Spectral and Time resolution
     • Combination of 2:1 bandwidth ratios and huge number of
       spectral channels
            • instantaneous spectral indices, rotation measures, uv-coverage
            • instantaneous velocity coverage
                53,300 km/s vs. current 666 km/s at 45 GHz
                lines at arbitrary redshift
     • Spectral flexibility
        • 128 independently tunable sub-bands (vs. 2 currently)
        • “zoom in” on the lines of interest
    • Temporal flexibility
           • Fast time recording: initially 100 msec; 2.6 msec possible
           • Pulsars: 1000 phase bins of 200 μsec width, 15 μsec possible
               pulsar searches, timing, etc. with an interferometer!
   • Spectral/temporal capability due to the WIDAR correlator

Sub-mm/mm Observing Techniques          The EVLA                         Aug 14, 2006
                                     The WIDAR correlator


  •    Designed and built in Canada at HIA
         – $15M USD – initially enabled Canada’s participation in ALMA via the North
           American Partnership in Radio Astronomy (NAPRA)
  •    8-GHz bandwidth in each polarization covered by 4 x 2-GHz bands
  •    Each of these 2 GHz bands covered by 16 sub-bands – each 128 MHz wide
  •    16,384 channels at 8 GHz bandwidth
  •    4,194,304 channels possible
  •    2 MHz – coarsest frequency resolution
  •    0.12 Hz – finest frequency resolution
  •    Time sampling (up to 20 ms)
  •    And lots more……………………………………………………




Sub-mm/mm Observing Techniques           The EVLA                               Aug 14, 2006
Sub-mm/mm Observing Techniques   The EVLA   Aug 14, 2006
                                   EVLA Design Driven By
                                    Four Science Themes
                      Magnetic Universe              Obscured Universe
 Measure the                                                             Image young
 strength and                                                          stars and massive
  topology of                                                            black holes in
   the cosmic                                                          dust enshrouded
magnetic field.                                                          environments.
                                                       Sgr A*


                     Transient Universe              Evolving Universe

Follow the rapid                                                            Study the
  evolution of                                                           formation and
    energetic                                                             evolution of
  phenomena.                                                             stars, galaxies
                                                         CO at z=6.4       and AGN.

  Sub-mm/mm Observing Techniques          The EVLA                         Aug 14, 2006
                    Key EVLA Correlator Capabilities

                                             8 GHz Bandwidth (dual polarization).
Deep Imaging                                 Full polarization processing.
Polarization                                 Wide-field imaging.

                                               16,384 channels at max. bandwidth (BW).
                                               >106 channels at narrow BWs.
Narrow spectral lines                          Spectral resolution to match any linewidth.
Wideband searches                              Spectral polarization (Zeeman Splitting).


                                             Eight 2 GHz wide bands input.
Flexibility                                  Each input band decomposed into 16
                                                 tunable sub-bands of adjustable width
Many resources                               Gives 128 independent sub-bands


                                             1000 pulsar “phase bins”.
                                             “Single-dish” data output to user
High time resolution                          instruments.
                                             Very fast time sampling (20 ms).


Sub-mm/mm Observing Techniques   The EVLA                                    Aug 14, 2006
                                 Synergy with ALMA
  •    High-redshift star-forming galaxies
         – CO lines from star-forming galaxies
            • Key science goal of ALMA
            • At redshifts of a few CO J=1-0 and 2-1 line in EVLA bands
            • At high redshifts (z~6) CO J=3-2 line in EVLA bands
         – EVLA will detect synchrotron component out to z ~ 3 (normal) or z~5 (ultraluminous)
            • contribution of AGN
         – EVLA will detect free-free emission from HII regions out to z~ 2
         – EVLA will be able to detect dust continuum out to redshifts > 10
  •    Young & proto-stellar objects
         – ALMA “bread and butter” – so where does the EVLA come in?
         – Defeat high dust opacity in the densest regions – opaque to 10’s of GHz
         – identify dust from free-free from synchrotron emission




Sub-mm/mm Observing Techniques           The EVLA                               Aug 14, 2006
        Star-Forming Galaxies at High Redshift
• Enabled by EVLA sensitivity
   –Synchrotron emission: AGN,
    SNR
   –Free-free emission: HII regions
   –Thermal dust emission
• Resolution 50 mas
   = 200 pc @ z=10                               Spitzer



• EVLA+ALMA
  – similar sensitivity
  – dust+ionized gas+NT
  –SED over 3-orders of magnitude
                                                            ionized gas
   in frequency
  – large range of redshift




                                                           Arp220 SED scaled to high redshifts.
   Sub-mm/mm Observing Techniques     The EVLA                                     Aug 14, 2006
                Molecular lines in High-Redshift
                    Star-Forming Galaxies
  •Currently:
     –50 MHz (z range of 0.001 at 50 GHz!)
     –Need to know a precise redshift or be lucky!
     –8 spectral channels = no frequency resolution


  • No z searches
  • Very poor spectral resolution
  • Each line must be done
   independently (CO, HCN, HCO+,
   …)



             COJ=3-2 Z = 6.42 Peak ~ 0.6 mJy

                     Carilli, Walter, & Lo


Sub-mm/mm Observing Techniques                 The EVLA   Aug 14, 2006
                Molecular lines in High-Redshift
                    Star-Forming Galaxies
• EVLA:
   –8 GHz bandwidth @ 40-50GHz (z=1.4 -1.9 for CO J=1-0; z=3.8 to 4.8 for J=2-1)
   –16384 spectral channels at maximum bandwidth
   –Searches are a piece of cake!
   –Other lines: HCN, HCO…..




             Arp 220 @ z=8

             Red line = EVLA in 8 hrs

             CO J=1-0 @ 12.7 GHz
                J=2-1 @ 25.6 GHz
                J=3-2 @ 38.3 GHz
Sub-mm/mm Observing Techniques          The EVLA                    Aug 14, 2006
                             EVLA Setup for CO Z-Search
                                                Sky Frequency Bands
                                    1-2   2-4   4-8       8-12     12-18 18-27   27-40   40-50 GHz
                                     L     S     C         X         U    K       Ka        Q

                                                                                 8 tunable IF Bands

• 42-50 GHz band provides lowest                          Right Polarization                                Left Polarization
redshift.
• z = 1.4 to 1.9 for J=1-0.
                                                              48-50 GHz                                         48-50 GHz
• z = 3.8 to 4.8 for J=2-1.
• v ~ 5.0 km s-1 (1 MHz).                                    46-48 GHz                                         46-48 GHz

• 200 km-s-1 galaxy would occupy
~40 channels.
                                                              44-46 GHz                                         44-46 GHz
• Interferometry
     • High resolution imaging.                               42-44 GHz                                         42-44 GHz

                                                16 Sub-Bands (shown with default positions and widths)
                                                                                                                Note: Sub-bands can be
                                                                                                                seamlessly joined across
                                                 1    2   3    4   ...                              15 16
                                                                                                                each observing bandwidth.
                                                          2, 1, 0.5, ... GHz Observing Bandwidths


   Sub-mm/mm Observing Techniques               The EVLA                                                          Aug 14, 2006
                    Magnetic Fields in the ISM
~30 H+ recom lines within 4 MHz      2 GHz
 band width (also He+, C+)                                               Sky Frequency Bands
                                             1-2      2-4            4-8         8-12    12-18   18-27   27-40     40-50   GHz

• Each line individually targeted             L        S              C           X        U      K        Ka         Q


• Zoom in – 128 to 4 MHz
                                          Right Pol'n                                        Left Pol'n
• Each of 62 spectra gets 256           Continuum Setup                                          Continuum Setup

  channels
     •  = 15.6 kHz (1.6 km/s)
• EVLA imaging gives:
     •Gas density
     •Temperature
     •B-field (Zeeman splitting is
     weak - 2.8 Hz/mG)                                                   HII
                                                                  HeII

     •Improve SNR by “stacking”
                                                            CII                25 km/s      1024 chan's.
                                                                                          Recirc. factor = 16
                                              8 MHz                                        v = 0.8 km/s
                                              (800 km/s)
                              Many Spectral Lines at once!
                                                            Sky Frequency Bands
                                                1-2   2-4   4-8   8-12   12-18 18-27   27-40   40-50 GHz
•   Nobeyama obs of TMC-1.                       L     S     C     X       U    K       Ka        Q
•   414 lines (8 to 50 GHz)
•   38 species
     – including “heavy” molecules
                                          Kaifu et al., 2004.                8 GHz
     – Slow rotators
•   Some may show Zeeman
    splitting.
•   EVLA can observe 8 GHz at once
                                    TA*
     – an average of 80 lines
     – EVLA Correlator can “target”
          many (~60) lines at once.




    Sub-mm/mm Observing Techniques         The EVLA                                       Aug 14, 2006
                                 EVLA Project Status

  • Six (of 27) antennas currently withdrawn from VLA service, and
    being outfitted with new electronics.
         – Two antennas are fully outfitted, are now part of regular VLA
           observations
         – Two others being outfitted with final electronics, and under test.
           Available for astronomical use by late summer.
         – Two others in early stages of outfitting.

  • Antennas will be cycled through the conversion process at a rate six
    per year, beginning in 2007.




Sub-mm/mm Observing Techniques           The EVLA                           Aug 14, 2006
                              New Capabilities Timescale
•      The old correlator will be
       employed until the new
       correlator achieves full
       27-antenna capability –
       mid 2009.
•      Full band tuning
       available before 2009, on
       schedule shown here.




    Sub-mm/mm Observing Techniques     The EVLA            Aug 14, 2006
                                 Major Future Milestones
  • Test prototype correlator                                        mid 2007
         – Four antenna test and verification system
         – Not available for science
  • Correlator installation and testing begins:                      mid 2008
         – Capabilities will rapidly increase until mid 2009.
  • Correlator Commissioning begins:                                 mid 2009
         – VLA correlator turned off
         – New correlator capabilities will be much greater at this time.
  • Last antenna retrofitted                                            2010
  • Last receiver installed                                             2012




Sub-mm/mm Observing Techniques           The EVLA                           Aug 14, 2006
                                 Summary
  • The EVLA will improve the VLA capabilities more than tenfold
    through up-to-date receivers, data transmission and the WIDAR
    correlator
  • The project is on-track for completion in 2010 (antennas and
    correlator), and 2012 (for all frequency bands).
  • The HIA-designed WIDAR correlator is an essential and critical
    component of the EVLA.
  • Powerful new capabilities will begin to be available in 2008
         – just two years from now!




Sub-mm/mm Observing Techniques        The EVLA                Aug 14, 2006
           The EVLA: A North American Partnership




                        Project info: http://www.aoc.nrao.edu/evla/
Sub-mm/mm Observing Techniques             The EVLA                   Aug 14, 2006

								
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