Data model: photoMatchPlate

General description: These files contain the match of each plate to SDSS photometry, sorted in the same way as the specObj file. There are two matches: a pure positional match, and a flux-based match. The flux-based match is the default to use. The positional match finds the nearest primary object within 2 arcsec, or if there is none, identifies the primary field covering the given position. The actual data for the flux-based match can be found in the photoPlate file.

The flux-based match identifies objects that failed the non-positional match, and things for which the aperture flux of the child is low relative to the fiberflux (which is based on the parent). For such objects, it asks what parent (if any) covers the desired match position. If no parent exists, there is no valid match at all. If a childless parent exists, that is used as the match. If a parent with multiple children exists, images are made of all the children based on the atlases, and child that contributes the most flux within 1.5 arcsec radius of the match location is selected. For real objects this procedure works remarkably well.

The status of the match is recorded in the FLUXMATCH_STATUS bitmask, whose bits have the following meanings:

0 - ORIGINAL_FLUXMATCH - used the original match (which exists)
1 - FIBER_FLUXMATCH - flagged due to fiberflux/aperflux issue
2 - NONMATCH_FLUXMATCH - flagged due to non-match
3 - NOPARENT_FLUXMATCH - no overlapping parent in primary field
4 - PARENT_FLUXMATCH - overlapping parent has no children, so used it
5 - BRIGHTEST_FLUXMATCH - picked the brightest child

The original positional match information is stored in ORIG_ID, ORIG_RA, ORIG_DEC. (The flux-based match is ALWAYS taken from the same primary field).

In this directory, we also put QA plots for objects that have significant corrections: any spectrum with an OBJTYPE that isn't "SKY" but don't have FLUXMATCH_STATUS equal to 1. For example, this QA plot shows an example where we targeted a fleck from large galaxy on the sky, and the flux-based matching correctly matches it to the full object (which dominates the flux in the fiber).

Naming convention: photoMatchPlate-PLATE4-MJD.fits

Approximate size: 100 kbytes.

File type: FITS

Read by products: sas

Written by products: sas

Required header keywords:

Required column names:

Example file: photoMatchPlate-2292-53737.fits