NYU Value-Added Galaxy Catalog

object_catalog.fits

This file is the master file which has an entry for each object in the value-added galaxy catalog, its position on the sky, and its tag and index number in each constituent catalog. Essentially it is a book-keeping device. Also, it is the smallest file which contains all of the information about which objects are in which catalogs.

Note that the catalog is defined such that every object is some entry in the SDSS imaging catalog. Not all such entries will have entries in the other catalogs.

The first three columns of this file are:

  1. OBJECT_TAG: just an index number
  2. RA: Right ascension, J2000, degrees
  3. DEC: Declination, J2000, degrees

Then for each catalog "CATALOG" there are two entries:

  1. CATALOG_TAG: which is a tag number in the constituent catalog which may or may not have some meaning
  2. CATALOG_POSITION: which is simply the position of object in our copy of the the constituent catalog (which lives in a subdirectory --- this does not refer to the object_CATALOG.fits file.

Our copy of the constituent catalog "CATALOG" is always in: 

CATALOG/CATALOG_catalog.fits
These files contain the catalog information. There are typically more entries in this file than are matched in object_catalog.fits (since, for example, not all 2MASS sources are in the SDSS imaging survey).

For each constituent catalog there is also a file:

CATALOG/CATALOG_objects.fits
which contains two columns:
  1. OBJECT_TAG: the index number in object_catalog.fits of the match for this entry of the full catalog
  2. OBJECT_POSITION: the zero-indexed position of the match in object_catalog.fits
This file allows you to start with the given catalog and ask what matches to it there are in the SDSS.

NYU Value-Added Galaxy Catalog