Si Simulating blending ef effects on statistical mea easurem - - PowerPoint PPT Presentation

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Si Simulating blending ef effects on statistical mea easurem - - PowerPoint PPT Presentation

Jan 20, 2024 278 likes •500 views

Si Simulating blending ef effects on statistical mea easurem emen ents of of galaxi xies es Erfan Nourbakhsh (UC Davis) August 14, 2018 Tucson, Arizona 1 Credit: journey.ritzcarlton.com Galaxy blending - as a 2D phenomenon -

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Si Simulating blending ef effects on statistical mea easurem emen ents of

  • f galaxi

xies es

Erfan Nourbakhsh (UC Davis)

August 14, 2018 Tucson, Arizona

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Credit: journey.ritzcarlton.com

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  • Galaxy blending - as a 2D phenomenon - affects:
  • Shape measurements
  • Number counts
  • Fluxes and colors
  • Blending will affect Clustering+WL cosmological probes (differently)
  • How sensitive is the inferred cosmology to blending?

What if we combine multiple cosmological probes?

  • Blending imitation using the truth (simulation)
  • Analysis
  • Two-point statistics results
  • Covariance matrix
  • Cosmological parameter estimation
  • Summary

Dawson+16

RED: Subaru GREEN: HST

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3 Bin 1 Bin 2 Bin 3 Bin 4

z

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| Same Underlying Dark Matter |

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  • Buzzard_v.1.6 (DeRose et al. 2028, in prep.)
  • We imitate blending by finding close pairs within a separation

angle threshold that gives the predicted blend fraction by Dawson+16 ~ 10% for our sample

5 ! " "# "$ <1.5’’ proximity C: luminosity centroid !: position vector

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6 LSST i<23

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Galaxy-Galaxy

Unblended Blended

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8 blended - unblended

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Shear-Shear

Unblended Blended

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Shear-Shear

Ω" = 0.29, )* = 0.82 Ω" = 0.27, )* = 0.89

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Shear-Shear

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Galaxy-Shear

Unblended Blended

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Galaxy-Shear

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  • Blending affects the extracted cosmology from the

cosmological probes differently

  • There is a selection bias due to blending
  • Our cosmological probes are >3D and the effect we are

correcting for (blending) happens in 2D (although it indirectly affects the third dimension through photo-z)

  • Our goal is to see if these effects can be suppressed if we

jointly analyze multiple 3D probes since they share the same dark matter distribution

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! " #

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Buzzard_v.1.6 (DeRose et al. 2028, in prep.) – I had to fix some bugs 143 jackknife regions to get the sample variance and covariance matrix

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  • DC2 image-based catalog can be used instead of

Buzzard and can give us more realistic results

  • Convolving our shears with a ground-based PSF that

circularizes all galaxy images

  • To test if we can decrease the systematic error by

throwing out blends that are likely to have color gradient

  • A better covariance matrix for the joint probes is crucial

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