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  1. Data Management
  2. DM-8059

Failure to identify red-sequence galaxies in the cores of clusters

    Details

    • Type: Story
    • Status: Done
    • Priority: Major
    • Resolution: Done
    • Fix Version/s: None
    • Component/s: None
    • Labels:
      None
    • Templates:
    • Story Points:
      8
    • Sprint:
      DRP S17-2
    • Team:
      Data Release Production

      Description

      When attempting to identify galaxy clusters in the HSC data via the red-sequence cluster finder CAMIRA, it was found that galaxies near the cluster center were entirely missing. One likely cause of this is that the deblender is failing in one or more bands causing incorrect measurements of the colors. This appears to be true for different flux measurements. In the short term we have attempted to fix this by measuring colors in fixed apertures on the parent images, but we need to find what is the root cause.

      Here is an example of a cluster at redshift z=0.74 with missing galaxies near the center. The circled galaxies are those identified as part of the cluster.

      Running sextractor on the same -i-band data and comparing 2" shows a number of outliers.

      If you plot the position of these outliers, many of them correspond to the cluster members at the center. The outliers also correlate well with the blendedness parameter.

      The position of this cluster is RA=32.8119 and Dec=-3.723. There is another example of this at RA=215.97466 Dec=-0.43444. It is estimated that 20% of large clusters suffer from this problem.

        Attachments

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        3. example3.png
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        5. example5.png
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        6. members.jpg
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        7. nominal_member_color.png
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        8. nosmooth_member_color.png
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        9. outliers.jpg
          outliers.jpg
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        10. sextractor.jpg
          sextractor.jpg
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                • Assignee:
                  rearmstr Bob Armstrong
                  Reporter:
                  rearmstr Bob Armstrong
                  Watchers:
                  Bob Armstrong
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                    Updated:
                    Resolved:

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