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Biases of model magnitude for red galaxies #90
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Documenting a Slack thread with @chto and Risa from earlier this month. Work on this ticket continues (but no PR yet).
Finally, here's this object in the viewer. There's a nearby companion but it's not clear to me that the photometry would be biased in the direction of being too red based on the nearby source-- |
Following up on the extensive new modeling capabilities incorporated in #95, it is clear that--for this particular test object--it's the data that are (unphysically) red. And in fact you can see from the image cutout that the photometry for this target may be compromised by the nearby companion. |
@chto can you please review the latest model fitting results in Iron and let me know if the model colors have improved. I do believe that the deviations you've documented are unrealistically red observed colors which are due to measurement noise. |
@chto hopefully this issue is resolved, but if not please feel free to re-open. |
@moustakas It seems that the colors based on the best-fit model are biased blue for red galaxies. This bias becomes more pronounced for low redshift galaxies.
The following plot, based on the
fastphot-fuji-sv1-dark.fits
catalog, demonstrates this finding. I first cut out galaxies with DES>0 to make sure DECAM filter is used for calculations. The y-axis is the fractional error of color based onFLUX_SYNTH_MODEL_band
and color based onFlux_band
. Triangles with the error bar show the median and error of the median. The blue band shows the histogram of the samples going into the median calculation. The top panel shows low redshift galaxies while the bottom panel shows the full samples.Since the width of the redsequence is ~0.025, it would be great to have biases smaller than this value.
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