GALEX-SDSS photometric redshifts: Training set

We compare here the photometric redshift distribution obtained for SDSS galaxies (type = 3) and NUV < 22, from two different training sets.

Comparison of redshift distributions obtained with two different training sets

The red histogram on the plot shows the redshift distribution obtained using a training set including all GALEX-SDSS spectroscopic counterparts. The blue one shows the redshift distribution obtained using only the GALEX-SDSS spectroscopic counterparts with 1 to 1 GALEX-SDSS cross matches within 4 arcsec. The first training set yields a slight underestimation of the photometric redshifts at faint magnitudes, with respect to the second one.
A first quick visual inspection of a few GALEX-SDSS 1 to many cross-matches suggests that brightest objects are actually shredded in SDSS (this seems to be the case for a significant fraction of the GALEX-SDSS spectroscopic counterparts), while the faintest are blended in GALEX. This obviously needs to be confirmed with inspection of more matches.
We use the training set using 1 to 1 GALEX-SDSS spectroscopic counterparts for the photometric redshifts presented hereafter.