Centre for Astrophysics and Supercomputing

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Wide-field, High Spatial Resolution Radio Imaging
of Nearby Starburst Galaxies
By Emil Lenc elenc_at_astro.swin.edu.au http//astron
omy.swin.edu.au/elenc/
Supervisor Dr. Steven Tingay Assoc.
Supervisor Prof. Matthew Bailes ATNF
Co-supervisor Dr. Tasso Tzioumis Proposed ATNF
Co-supervisor Dr. Tim Cornwell

• Centre for Astrophysics and Supercomputing
• Swinburne University of Technology

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Starburst Galaxies
McDonald, A.R., et al., 2002, MNRAS, 334, 912.
VLA A-Configuration and Pie Town image of M82 at
15 GHz
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Starburst Galaxies

• Measure Spectral Indices.
• Model free-free absorption.
• Estimate SN rate.
• Estimate SNR age for resolved remnants.

McDonald, A.R., et al., 2002, MNRAS, 334, 912.
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Southern Starbursts
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Achieving Wide-fields

• VLBI field-of-view limited by several factors.
• Primary beam, bandwidth averaging and
  time-averaging ideally planned for before
  observation.
• Non-coplanar effects can be accounted for
  post-observation.
• Faceting
• 3-D FFT
• w-Projection

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AIPS

• No new improved banana recipes -(
• but there is an implementation of the
  w-projection algorithm.
• Trivial to add w-projection to any existing
  imaging script.
• w-projection implementation adds little overhead
  compared to deconvolution.
• Used Briggs weighting (robustness2 approx.
  natural), BW synthesis, 6144x6144 image size, 11
  mas cell-size.

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The Long Baseline Array (LBA)
Baseline 1,700 km Resolution 10 mas
Baseline 558 km Resolution 50 mas
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NGC 253
Ulvestad, J.S. Antonucci, R.R.J., 1997, ApJ,
488, 621.
VLA 2.0cm A-configuration image of NGC 253.
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NGC 253
Ulvestad, J.S. Antonucci, R.R.J., 1997, ApJ,
488, 621.
VLA 20cm A-configuration image of NGC 253.
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NGC 253First Widefield LBA Observation
Tingay, S.J. 2004, ApJ, 127, 10.
LBA 20cm image of NGC 253 using 3 telescopes (At,
Pa, Mp) and 6 hours of observation time.
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NGC 253Widefield Imaging with LBA - Take Two
LBA 13cm image of NGC 253 using 4 telescopes
(ATCA, Tid., Parkes, Mopra) and 12 hours of
observation time.
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NGC 253Comparison with other radio observations
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NGC 253Comparison with other radio observations
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NGC 253 Free-Free Modelling Observed Sources
Xs mark sources detected by Ulvestad et al
(1997) at higher frequencies.
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NGC 253A Null Detection Still Tells Us Something!
Xs mark sources detected by Ulvestad et al
(1997) at higher frequencies.
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Free-free Absorption
SNR
HII
SNR (Tentative)
Background image H?NII emission line Dahlem,
M. 2002, JENAM Conference From Observations to
Self-Consistent Modelling of the ISM in
Galaxies, M. de Avillez D. Breitschwerdt
(eds.), p. 229
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5.48-43.3 - A Resolved SNR Ring
Radius of supernova 45 mas
Assuming free expansion of about 10,000 km/s
5.48-43.3 went supernova 80-90 years before this
observation.
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Comparison to Other Galacticand Extragalactic SNR
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Future Work

• Compare current results with multi-wavelength
  observations.
• Perform multi-epoch observations.
• Disk-based recording to enable greater
  sensitivity.
• Apply wide-field techniques to AGN-jet hot spots.

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Summary

• Have successfully used the LBA as a wide-field
  instrument.
• Modelled free-free absorption in 17 compact radio
  sources (HII and SNR).
• Resolved an SNR.
• More to come - Stay tuned!

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Online Wide-field Imaging Calculator
http//astronomy.swin.edu.au/elenc/Calculators/wf
calc.php
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Comparison of Position Errors