WideField Observing Strategies

1
Wide-Field Observing Strategies with the
WSRT Robert Braun (ASTRON)

• Outline
• Large Mosaics
• Ultra-sensitive Total Power
• Multi-grating beam modes
• Pulsar Surveys
• CRs from the Moon
• Simulated filled aperture
• FPA Proposal

2
Large Mosaics

• Historically interferometric imaging was
  constrained to a single primary beam, but large
  WSRT mosaics are now routine.
• eg. WSRT HI mosiac of M31
• 163 pointings on 15 arcmin
• Nyquist-sampled grid
• 350 hours observing
• Aug. 2001 Jan. 2002
• 50 pc x 2 km/s res. over the 80 kpc disk
• s 1.4 mJy/Beam (at DV 2 km/s)
• DNHI 1.0, 3.5, 11 and 24 x 1018cm-2
• _at_ 120, 60, 30 and 20 (DV20 km/s)
• extended rotation curve / warping
• outer HI edge / UV radiation field
• CNM / WNM in disk
• circum-galactic HI clouds and streams

3
Large Mosaics

• eg. WSRT HI mosiac of M31
• 50 pc x 2 km/s res. over the 80 kpc disk
• most detailed ISM cube yet made

Braun et al. 2002, 2005
4
Ultra-Sensitive Total Power

• Usually one thinks of synthesis arrays as
  providing high angular resolution at the expense
  of brightness sensitivity, but the opposite can
  also be achieved.
• eg. WSRT Wide-field HI Survey
• Auto-correlation drift-scan survey of 1800 deg2
  centered on M31
• 380 hours observing with 14 telescopes Aug.
  2002 Oct. 2002
• 48 arcmin x 17 km/s res. over 60 x 30 deg.,
  -1000 lt V lt 6500 km/s
• s 17 mJy/Beam (at DV 17 km/s), cf. HIPASS
  s14 mJy/Beam
• D NHI 4 x 1016 cm-2 for emission filling the
  beam (10 kpc at 700 kpc)
• (cf. HIPASS D NHI 4 x 1017 cm-2 in 15 arcmin
  beam)
• Galactic CHVCs
• Magellanic Stream and Wrights HVC complex
• circum-galactic HI clouds and streams of M31 and
  M33

5
Ultra-Sensitive Total Power

• eg. WSRT Wide-field HI Survey (Braun Thilker
  2004)
• gt 100 newly detected compact features
• Mag. Stream apo-galacticon tail, Wrights Cloud
• faint, compact pop. centered on M31 systemic
  velocity
• M31 M33 cosmic web filament

6
Ultra-Sensitive Total Power
The M31 M33 filament

• connects VSYS of M31 and M33
• continues in anti-M33 direction (300 kpc total
  extent)
• filamentary structure within 30 kpc
• connects to ongoing fueling of both M31 and M33
• confirms 30-fold increase in HI covering factor
  1019 1017 cm-2
• first image of a Lyman Limit absorption System

Braun Thilker 2004, AA, 417, 421
wide-field WSRT data
7
Maximizing Utility of a Grating Array
WSRT Array Geometry

• East West one dimensional array, 14 telescopes
  of 25 m
• ten telescopes (RT0 RT9) always form grating
  array
• normal imaging done with judicious placement of
  RTA D
• But, there are circumstances when a 12 telescope
  grating array can be very advantageous!
• equivalent sensitivity of 87 m filled aperture,
  FOV of 25 m tel.

8
Maximizing Utility of a Grating Array

• eg. Pulsar Surveys
• instantaneous response is set of grating fan
  beams
• WSRT IF system has 8x20 MHz independent bands
• tune all IFs to same freq.
• steer delay- and phase-tracking centers for each
  of the 8 IFs to fill primary beam with grating
  beams
• reconstruct time series for each synthesized beam
  after the fact
• full primary beam FOV with coherent sensitivity

9
Maximizing Utility of a Grating Array

• eg. 8gr8 Pulsar Survey (Stappers et al. 2005)
• first multi-grating beam pulsar survey has now
  been carried out l 92 cm, BW 10 MHz, l 220
  280, b -1.5 6.
• 144 hr in August 2004, plus 144 hr in early 2005
• 2 hr integration per position for detection
• 2 hr integration per position for confirmation (6
  months later) using perpendicular Hour-Angle
  coverage

10
Maximizing Utility of a Grating Array

• eg. 8gr8 Pulsar Survey (Stappers et al. 2005)
• example of pulsar candidate in initial and
  confirming obs.
• yields position to sub-arcmin and period
  derivative

11
Maximizing Utility of a Grating Array
Pulsar Survey Figure of Merit M FoV x (A/T)2 x
BW x n-3.6

• PuMa now gives 8x10 MHz, but PuMa II will give
  8x20 MHz
• hard to compete at 20cm with Parkes Arecibo
  multi-beam systems (need FPAs and more BW)
• already defines state-of-the-art at low
  frequencies

12
Maximizing Utility of a Grating Array

• eg. NEW Moon Project (KVI/ASTRON)
• high energy CRs expected to produce nanosec
  radio bursts after interaction with lunar surface
  (SLAC calibration)
• near 150 MHz radio signal is almost isotropic so
  entire lunar surface useful as detector (although
  1/B strongly dilutes signal)
• base-band recording with Puma (II)
• use grating beams to cover entire lunar surface
  at coherent array sens.
• predicted count rate is very(!) competitive (1
  100 /hr)
• first test obs. done in June 2005

13
Maximizing Utility of a Grating Array

• Typically one has had to choose between the
  brightness sensitivity of a total power
  observation or the well-defined PSF and excellent
  spectral baseline properties of an
  interferometer, but the two need not be mutually
  exclusive.
• eg. simulated filled aperture
• simulate filled aperture by observing at extreme
  HAs where projected telescope separation
  aperture size
• grating array (12x144 m) becomes filled
  aperture (25x300 m)
• brightness sensitivity of single dish telescope
• spectral baseline quality of interferometer
  (gt1041)
• well-defined PSF of interferometer (gt1041)
• FOV of 25m dish with beam of 25x300m dish

14
Maximizing Utility of a Grating Array

• eg. Imaging the low-z Cosmic Web (Braun et al.
  2005)
• probe extended environments of gt 340 galaxies
  within 40 Mpc with a 22,000 pointing mosaic, DNHI
  2 x 1017 cm-2 over DV20 km/s
• survey (1000 hr) begun in December 2004, now 45
  complete

15
Proposed WSRT FPA System Parameters

• Frequency Band 850 1750 MHz (bottom end by TV
  RFI, top end from OH lines)
• Dual Polarization
• Instantaneous BW minimum of 320 MHz (to be
  competitive with other L-band systems) preferred
  goal of 1 GHz (ie. entire band)
• Tsys lt 50 K, hA gt 70
• Freq. resolution 20 kHz over full BW or finer
  for smaller BW (corresponds to 4 km/s for the HI
  line)
• Instantaneous FoV 25 primary beams (formed from
  the 100 elements of each FPA)
• Correlation 1414 for each of 25 beams, full
  polarization
• Wide-field application efficiency 25/4 6 x
  EVLA
• Timeline Funding request Sept. 2005, FPAs 2008,
  back-end 2009

16
What will become possible?

• Survey programs are 50 times faster, so 7 times
  deeper in the same total integration time
• Continuum Sensitivity lt 7 mJy in 12 hours
  over 13 deg2
• 
  20 mJy 130 deg2
• 
  70 mJy 1300 deg2
• spanning 850 1750 MHz gt RM synthesis,
  spectral shape
• The Magnetic Universe (conf. limit in Q,U,V
  perhaps 1 mJy)
• produce RM grid from Galactic pulsars plus
  background AGN at various distances with 7 mJy
  rms (12 hr obs) get detected polarized source
  density of 100 deg-2
• Constraining Dark Energy (all-sky HI survey)
• get 106 galaxy in 2x104 deg2 at z lt 0.25 in 3
  year survey
• Ultra-deep HI Synthesis (in semi-shadowed mode)
• will approach DNHI 1016 cm-2 over DV20 km/s

17
What will become possible for Pulsars? Survey
Figure of Merit M FoV x (A/T)2 x BW x n-3.6
70 times the 2005 state-of-the-art at 20 cm !!
18
Wide-Field Observing Strategies with the WSRT

• Summary
• Large Mosaics
• Ultra-sensitive Total Power
• Multi-grating beam modes
• Pulsar Surveys
• CRs from the Moon
• Simulated filled aperture
• FPA Proposal

Still plenty of scope for innovation !
19
(No Transcript)