STEP 2: Results
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Shear TEsting Programme 2: Results

Download a plot of STEP2 results

This is the main result plot which shows, for each author analysis (ID key), the parameters m and c for both components of shear. The different colours are for the different PSF models. In those cases, where relevant, the large red triangle is the result from STEP1.

I'm afraid that this plot is a little busy, but the symbols and lines are as follows;

Solid lines = estimates of m and c from gamma (equation 9c)
dotted lines = estimates of m = (mA + mB)/2 and c=(cA - cB) where individual errors are added in quadrature and mA etc are calculated from equation 9a,b

The comparison of the solid and dotted error bars show the difference between statistical shot noise and statistical shear measurement noise.

The circle symbol (o) is positioned at (mA,c)
The triangle symbol is positioned at (mB,c)

The comparison of these two symbols show how stable the shear calibration errors m are to image rotation. Often they are very close, as expected, but in some cases they are very different. Note the same set of matched galaxies are included in both the original and rotated analyses so this is not a selection effect.

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Download more information:

The following data files containing these results can be downloaded;

  • mc_table.dat
  • mc_1_table.dat
  • mc_2_table.dat
  • shear_in_out.tar.gz

    mc_table.dat contains the results from the full STEP2 analysis which combines the original and rotated images. The format is as follows

    ID PSFpair selc 1 m1 +/- err c1 +/- err
    ID PSFpair selc 2 m2 +/- err c2 +/- err

    where the fourth column denotes the shear component.

    The files mc_i_table.dat contain slightly more information. The format is as follows

    ID PSForig all m_orig +/- err c_orig +/- err
    orig selc mA +/- err cA +/- err
    rot selc mB +/- err cB +/- err
    pair selc m +/- err c +/- err

    Columns 4-5 are simply the plotted points and should be self explanatory (selc means the results come from the matched catalogues). The first row are the results that you would have received back from the original STEP2 analysis which contain all your objects. mc_1_table.dat contains the results for the gamma_1 component. mc_2_table.dat contains the results for the gamma_2 component. Comparing row 1 and row 2 tells you about the effect that matching the original and rotated catalogues have introduced. In general the changes are very small.

    The tar file shear_in_out.tar unpacks into individual directories for each author, and plots the measured shear against the input shear for each shear component and PSF. Over-plotted are the best-fit lines. Each directory contains 4 files;

    • original_analysis.ps contains the results from the original image catalogues.
    • orig_pair_analysis.ps contains the results from the original image catalogues with a selection criteria that the object must also be included in the rotated catalogues.
    • rot_pair_analysis.ps contains the results from the rotated images catalogue with a selection criteria that the object must also be included in the original catalogues.
    • pair_analysis.ps contains the results from combining the information in the matched original and rotated catalogues and thus removing the shape noise contribution (you'll see the error bars significantly decreasing between this plot and the others).

    Back to the main STEP2 results page

    • Last modified 21st March.
    STEP pages maintained by Catherine Heymans: heymans[at]physics.ubc.ca