  Using ~1,700,000 target- and sky-fiber spectra from the SDSS, we have carried
out a systematic search for Galactic planetary nebulae (PNe) via detections of
the [OIII] 4959, 5007 lines. Thanks to the excellent sensitivity of the SDSS
spectroscopic surveys, this is by far the deepest search for PNe ever taken,
reaching a surface brightness of the [OIII] 5007 line down to about 29.0
mag./arcsec^2. The search recovers 13 previously known PNe in the Galactic
Caps. In total, 44 new PN candidates are identified, including 7 candidates of
multiple detections and 37 candidates of single detection. The 7 candidates of
multiple detections are all extremely large (between 21' - 154') and faint,
located mostly in the low Galactic latitude region and with a kinematics
similar to disk stars. After checking their images in Ha and other bands, three
of them are probably HII regions, one is probably associated with a new
supernova remnant, another one is possibly a true PN, and the remaining two
could be either PNe or supernova remnants. Based on sky positions and
kinematics, 7 candidates of single detection probably belong to the halo
population. If confirmed, they will increase the number of known PNe in the
Galactic halo significantly. All the newly identified PN candidates are very
faint, with a surface brightness of the [OIII] 5007 line between 27.0 - 30.0
mag./arcsec^2, very challenging to be discovered with previous techniques and
thus may greatly increase the number of "missing" faint PNe. Our results
demonstrate the power of large scale fiber spectroscopy in hunting for
ultra-faint PNe and other types of emission line nebulae. Combining the large
spectral databases provided by the SDSS and other on-going projects (e.g. the
LAMOST Galactic surveys), it is possible to build a statistically meaningful
sample of ultra-faint, large, evolved PNe, thus improving the census of
Galactic PNe.
