The tables below give the translations of the various numerical codes used in the MGC.
     
    Classification parameter CLASS:
    0    Unclassified
    1 Galaxy
    2 Reserved for morphological classification of galaxies
    3 Reserved for morphological classification of galaxies
    4 Reserved for morphological classification of galaxies
    5 Currently unused
    6 Currently unused
    7 QSO
    8 Star
    9 Asteroid
    10 Satellite trail
    11 Cosmic ray
    12 CCD defect
    13 Diffraction spike
    14 Other (noise)
    15 Obsolete (ie. replaced by a new catalogue entry)
     
    Photometric quality parameter QUALITY:
    This parameter describes the reliability of an object's photometric parameters depending on the level of
    • contamination by CCD defects satellite trails, cosmic rays and diffraction spikes;
    • blending with a similarly bright object;
    • missing light due to a CCD edge;
    • failed background estimation due to nearby very bright objects.
    0 Unclassified
    1 Photometric parameters are reliable.
    2 Photometric parameters are probably ok.
    3 Photometric parameters are unreliable. All objects with QUALITY=3 lie in exclusion regions.
     
    Extraction flags FLAGS:
    This is a SExtractor parameter. It contains all the possible extraction flags as a sum of powers of two. The following is taken from the SExtractor manual:
    2 The object has neighbours bright and close enough to significantly bias the MAG_AUTO photometry, or bad pixels (more than 10% of the integrated area are affected).
    4 At least one pixel of the object is saturated (or nearly so).
    8 The object is truncated (too close to an image boundary).
    16 The object's aperture data are incomplete or corrupted.
    32 The object's isophotal data are incomplete or corrupted.
    64 A memory overflow occurred during deblending.
    128 A memory overflow occurred during extraction.
     
    Exclusion region flag INEXR:
    Normally you should only use objects with INEXR=0.
    0 or F Object is not in an exclusion region.
    1 or T Object is in an exclusion region.
     
    Spectroscopic quality parameter Z_QUAL:
    Normally you should only use redshifts with Z_QUAL >= 3.
    1 Something is clearly wrong with the spectrum or there is absolutely no flux. Redshift measurement is not possible. Redshifts with this Z_QUAL are meaningless.
    2 Low quality spectrum. Probability that redshift is correct is low.
    3 Reasonable spectrum. Redshift is probably correct.
    4 or 5 Good or very good quality spectrum. Very reliable redshift.
    9 The database contains no spectroscopic information for this object.
     
    Redshift type parameter ABEMMA:
    0 Absorption and emission
    1 Absorption
    2 Emission
    3 Manual

     

     
    Fits file header keywords EXTNAME and EXTVER:
    These keywords can be used to easily address the first fits file extension that contains data from a given source.
     
    EXTNAME EXTVER
    MGC - -
    SDSS imaging IMAGE 2
    MGCz SPECTRUM 1
    SDSS SPECTRUM
    or
    OBJECT_DATA    		 2
    2dFGRS SPECTRUM
    or
    OBJECT_DATA    		 3
    2QZ SPECTRUM
    or
    OBJECT_DATA    		 4
    NED OBJECT_DATA 5
    PF OBJECT_DATA 6
    LSBG OBJECT_DATA 7

     

     
    Other non-MGC parameters and flags:

    • SDSS stuff:
      • type
      • flags
      • status
      • primTarget
      • secTarget
      • zStatus
      • specClass
      • zWarning

    • 2dFGRS description of classification parameters IGAL and JON.
    • SuperCOSMOS Sky Survey description of their classification and quality flags which are included in the 2dFGRS. See also this.

    • 2QZ identification and redshift quality parameter (taken from S. Croom et al., 2004, MNRAS, 349, 1397):
      1    High quality.
      2 Poor quality.
      3 No identification or redshift assignment.
     

    Joe Liske