Download - Point Source Subtraction
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Point Source Subtraction
Bart Pindor University of Melbourne
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Objectives•Remove Bright EG point sources prior to
polynomial EOR FG subtraction•Issue: Mode-mixing / ‘Frizz’•RTS will Peel some bright sources as part
of CML•It will be possible/necessary to remove
further sources after imaging•Characterize residuals/effect on (the
other) PS
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Importance of PS Subtraction
Liu et al. 2008
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MWA Beam
> 1%
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Matched Filters•Generally; positions, fluxes, spectra
unknown•Matched filter is the optimal linear S/N
estimator of source amplitudes
•Peaks in filtered maps used to identify PS€
D(x) = Aτ (x) + N(x)
Aest = ψ (x)D(x)dx 2∫ˆ ψ ∝ ˆ τ /P(k)
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Matrix Filters •Extension of Matched Filters to multi-channel •Developed for Planck CMB maps (Herranz et
al. astro-ph/08082884•Incorporates cross-channel correlations but
allows for independent spectral slopes
•Each filtered image estimates source fluxes
€
wl (k) = ψ lmm∑ (k)Dm (k)
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Matrix Filters• MTXF applied to MAPS +
RTS 8s snapshot• Beam is a single simulated
position-independent point source
• Peak pixel is the inferred position
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Matrix FiltersISSUES:• Centroiding• Efficient beam
reconstruction• Iteration• Diffuse sky model
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Matrix Filters• Aim for frizz-free
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OOB – oh oh?• Sidelobes will appear from
sources outside of the primary beam
• Can we detect/locate sources in combined maps?
• Use of MWA survey or other (GMRT?) data to locate relevant source?
• What is the accuracy of calibration solution in that direction?
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Open Issues / Simulation To-Do:•Ionosphere•HEALPIX pixelization•Integration, co-addition, registration•Rotation synthesis•Peeling levels and residuals•Calibration / Beam Accuracy•OOB•8 minutes * 200 Channels * 5000 images
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Open Issues / Simulation To-Do:•Ionosphere•HEALPIX pixelization•Integration, co-addition, registration•Rotation synthesis•Peeling levels and residuals•Calibration / Beam Accuracy•OOB•8 minutes * 200 Channels * 5000 images
= 136 years!