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Known Issues with the Early Data Release

Definitions of all data columns referenced below (e.g. ZWARN) can be found here.

  1. Redrock templates do not include AGN-like galaxies with a mixture of broad and narrow lines. As a result, these types of galaxies are often fit equally well (or equally poorly) with either galaxy or QSO templates at the same redshift, which can also trigger ZWARN bit 2 (value 22 \(=\) 4) for LOW_DELTACHI2 since the \(\chi\)2 difference between the two fits is small, indicating an ambiguous answer.

  2. There are cases where Redrock is overconfident and reports ZWARN==0, i.e. no known problems, even though the fit is incorrect. This can include unphysical fits due to the over-flexibility of PCA template linear combinations. This is particularly true for sky fibers which have a higher fraction of ZWARN==0 than would be expected from purely random fluctuations. Users should be especially cautious in any search for serendipitous targets in nominally blank sky fibers.

  3. The Redrock galaxy fits extend to redshift \(z =\) 1.7, although the range 1.6 < \(z\) < 1.63 is only constrained by the [OII] doublet in the midst of significant sky background while 1.63 < \(z\) < 1.7 has no major emission line coverage. Thus 1.6 < \(z\) < 1.7 is particularly susceptible to unphysical fits. This was the motivation for the large-scale structure catalogs to only consider galaxies with \(z\) < 1.6.

  4. Negative TARGETIDs indicate positioners that were non-functional and thus were not pointing at a known science target. Although these are unique within a given TILEID, they are not unique values across different TILEIDs. Since these are not science targets, most users can discard any negative TARGETID targets. This has been fixed for Main Survey (not part of EDR) non-functional positioners in future data releases, where negative TARGETIDs will be unique.

  5. For most of the tiles in Target Selection Validation (sv1), proper-motion corrections were applied in Fiberassign when the tile was designed (he design date can differ from when a tile was observed). A consequence is that the (TARGET_RA, TARGET_DEC, and REF_EPOCH) values are altered to have a REF_EPOCH of the date that the tile was designed, which makes them differ from the input photometric column values. However, the information is correct and consistent with the photometry.

  6. In the coadded FIBERMAP tables, 0.03% of targets incorrectly have COADD_FIBERSTATUS==0 even though all of their data are masked. These result in ZWARN \(\neq\) 0 in the redshift fits, but quality cuts based solely upon COADD_FIBERSTATUS have a tiny amount of contamination.

  7. In the coadded FIBERMAP tables, MEAN_FIBER_RA and MEAN_FIBER_DEC record the average as-observed position of the fibers (in comparison to the intended positions recorded in TARGET_RA and TARGET_DEC plus proper motions PMRA, PMDEC, REF_EPOCH). The FIBERMAP coordinate coaddition incorrectly included exposures that had been excluded from the spectral coaddition, which can result in incorrect MEAN_FIBER_RA/DEC values. The same issue applies to the standard deviations recorded in STD_FIBER_RA/DEC. As a result, TARGET_RA/DEC are more reliable than MEAN_FIBER_RA/DEC, while noting that the actual positioning can vary by O(0.1”), which is still small compared to the ~1.5” diameter fibers.

  8. During Survey Validation, the SUBPRIORITY column was overwritten in the fiberassign files. These were propagated to the FIBERMAP extension of many data products. For additional information see Section 5.2 of Myers et al. (2023).

  9. A bug in the fiberflat humidity correction led to suboptimal removal of the dichroic absorption feature at the level of a few percent on some exposures, but the corrections are still an improvement over previous spectroscopic reductions, and the impact on final redshifts is very small. This affected some exposures that had already been processed before the bug was caught.

  10. FLUX_IVAR_W1 and FLUX_IVAR_W2 were not included in fiber assignment of commissioning tiles and have a filler value of -1.

  11. Some secondary targets have incorrect BRICKID and BRICK_OBJID assignments. For additional information see desispec pull request #1716.

  12. Tile 80870 (SURVEY=sv1, PROGRAM=other, FAPRGRM=sv1scndhetdex) has two tiles/cumulative/80870/ directories for nights 20210512 and 20210513, which propagated into two sets of entries for this tile in zcatalog/ztile-sv1-other-cumulative.fits and zall-tilecumulative-fuji.fits.

  13. The equivalent widths in the emline files are wrong (overestimated) by a factor (1+Z) ** 2; this affects both the per-tile and the per-healpix emline files; the code bug was present when running the fuji (EDR) and guadalupe productions; it has been corrected for subsequent productions (e.g. iron / DR1).