  We report a multi-objective campaign of targeted 21 cm HI line observations
of sources selected from the Arecibo Legacy Fast ALFA (Arecibo L-band Feed
Array) survey (ALFALFA) and galaxies identified by their morphological and
photometric properties in the Sloan Digital Sky Survey (SDSS). The aims of this
program have been (1) to confirm the reality of some ALFALFA sources whose
enigmatic nature suggest additional multiwavelength observations; (2) to probe
the low signal-to-noise ratio regime, below the ALFALFA reliability limit; and
(3) to explore the feasibility of using optical morphology, color and surface
brightness to identify gas-rich objects in the region of the Pisces-Perseus
Supercluster (PPS) whose HI fluxes are below the ALFALFA sensitivity limit at
that distance. As expected, the reliability of ALFALFA detections depends
strongly on the signal-to-noise ratio of the HI line signal and its coincidence
with a probable stellar counterpart identified by its optical properties,
suggestive of on-going star formation. The identification of low mass, star
forming populations enables targeted HI line observations to detect galaxies
with HI line fluxes below the ALFALFA sensitivity limits in fixed local volumes
(D < 100 Mpc). The method explored here serves as the basis for extending the
sample of gas-bearing objects as part of the on-going Arecibo Pisces-Perseus
Supercluster Survey (APPSS).

Astrophysics of Galaxies