# NED Spec-Z Catalogs - Mattia Vaccari @ University of the Western Cape - 15 January 2015

NB : NED entries with a non-null 'Redshift Flag' were excluded. This removes photometric redshifts
     as well as other redshift estimates of somewhat dubious reliability (see below).

Q.: Are the redshifts reported in NED spectroscopic or photometric? And what do the codes following the redshift mean?
A.: We adopt spectroscopic redshifts whenever they are available. Sometimes, however, only a photometric redshift is available for an object, or the source of a redshift is not clearly stated in the published paper. In those cases, we flag the redshifts if we know that they are not from spectroscopy. It is still possible, however, for photometric redshifts to slip in unflagged. In cases of doubt, we urge you to go back to the published paper to check the source of the redshifts.

When we can determine from the reference the Quality of a Basic Data redshift, we attach a code to it. Here is a list of the codes:
[blank]	 usually a reliable spectroscopic value
:	 an uncertain value
?	 a very uncertain (questionable) value
1LIN	 a spectroscopic value from a single line, assuming the line is known
EST	 an estimated value
LUM	 estimated from assumed luminosity for a brightest cluster galaxy (Nelson et al. ApJ 563, 629, 2001)
MFA	 a value from a matched filter algorithm (see Postman et al. AJ 111, 615, 1996)
MOD	 a modelled value
PHOT	 estimated using photometry
PRED	 a predicted value
SED	 a value from a spectral energy distribution
TENT	 a tentative value
TOMO	 a tomographic redshift for a lensing object (see e.g. Hennawi and Spergel ApJ 624, 59, 2005)
SN	 the redshift of a host galaxy determined from the expansion velocity of a supernova