v2

Overview of v2 Redshift Catalog Files

The v2 redshift catalogs are available starting from Data Release 2 (DR2). They significantly reorganize the column layout compared to v1 by splitting each catalog into three separate FITS files by column type, plus a per-exposure fibermap file. This reduces per-file sizes at the scale of the growing DESI data volumes.

For each SURVEY and PROGRAM, four files are produced for each of “ztile” and “zpix” prefixes:

  • SURVEY/(ztile|zpix)-SURVEY-PROGRAM.fits — core redshift and targeting columns

  • SURVEY/(ztile|zpix)-SURVEY-PROGRAM-imaging.fits — Legacy Survey imaging photometry columns

  • SURVEY/(ztile|zpix)-SURVEY-PROGRAM-extra.fits — all remaining columns (full Redrock output, TSNR2, emission line fits, QuasarNET, quality flags)

  • SURVEY/exp_fibermap/(ztile|zpix)-SURVEY-PROGRAM-expfibermap.fits — per-exposure fibermap

The ztile catalogs contain redshifts fit to coadded exposures of each tile but not across tiles. The zpix catalogs coadd data across tiles (by healpixel or uniqpix) before redshift fitting.

Additionally, the “zall” files contain catalogs combined across all surveys and programs:

Most users will be interested in the zall/zall-pix*.fits catalogs (across all survey/programs) or the SURVEY/zpix-SURVEY-PROGRAM.fits catalogs (specific to individual survey/programs)

New Columns in v2

v2 also introduces new redshift quality columns not present in v1:

  • Z_BEST: best redshift, choosing between the standard Redrock Z and the QuasarNET Z_QSO for QSO targets. It is the recommended redshift value for most users. The associated Redrock columns are ZERR_BEST, ZWARN_BEST etc.

  • Z_CONF: integer confidence level: 0=no confidence, 1=low confidence (ZWARN_BEST==0 but not LSS-quality), 3=high confidence (passes LSS quality cuts). A non-zero Z_CONF also requires GOOD_SPEC==True.

  • GOOD_SPEC: True if the spectrum is a science target with good hardware status.

  • GOOD_Z_{BGS,LRG,ELG,QSO}: per-tracer redshift quality flags passing LSS cuts.

Subdirectories

Files are stored under zcatalog/v2/{SURVEY}/ for per-survey catalogs and zcatalog/v2/zall/ for the all-survey combined catalogs.