Redshifts from sky fiber spectra

[julienguy]

Consider adding a false positive score based on the redrock fits of sky fiber spectra.
It helps making decision on the balance between flexibility and realism of the spectral models.

[moustakas]

This is a good suggestion @julienguy.

@forero can I assign this to you? One idea would be to use the same set of tiles chosen by bin/select_test_tiles but simply write out the OBJTYPE=='SKY' spectra. Thoughts?

[forero]

@moustakas @julienguy Sure, I can work on this, but I am not entirely sure about what I should do exactly. i.e., we start by taking the fibers with OBJTYPE=='SKY' in two different redrock productions, and then what comparison should we make? I hope you don't mind laying out the details a bit more.

[julienguy]

I would simply record the fraction of sky fibers with delta_chi2 > 9 and delta_chi2 > 16 and in the redshift range of each target class in order to get a measurement of the false positive rate.

[moustakas]

Actually, @forero, I think this is relatively easy for me to do. I'll report back here once I've implemented what I have in mind.

[moustakas]

OK, I have a sample of ~33k sky-fiber spectra written out based on the same set of representative main-survey (iron) tiles we're using for our nominal tests. The catalog is here:

/pscratch/sd/i/ioannis/Y3-templates/sample/sample-iron-main-subset-sky.fits

For the record, the coadded (cumulative-tile) spectra and (iron) Redrock results for this sample were gathered with:

rrevaluator/bin/Y3-templates --gather-coadds --inputsample=iron-main-subset-sky
rrevaluator/bin/Y3-templates --run-redrock --inputsample=iron-main-subset-sky --rrtemplates=PCA-Iron

But let's keep this ticket open until I've coded up the summary statistics @julienguy wants to see based on all the different template sets.

[forero]

@moustakas Did you rerun to code to generate the representative main-survey (iron) tiles? The list of tiles I shared with you ages ago was not reproducible (I did not initialize the random number generator). The committed version of https://github.com/desihub/rrevaluator/blob/main/bin/select_test_tiles generates reproducible results.