The Herschel Virgo Cluster Survey. XVII. SPIRE point-source catalogs and
  number counts
  We present three independent catalogs of point-sources extracted from SPIRE
images at 250, 350, and 500 micron as a part of the Herschel Virgo Cluster
Survey (HeViCS). The source positions are determined by estimating the
likelihood to be a real source for each peak on the maps and the flux densities
are estimated using the sourceExtractorTimeline, a timeline-based point source
fitter. Afterwards, each source is subtracted from the maps, removing a
Gaussian function in every position with the full width half maximum equal to
that estimated in sourceExtractorTimeline. This procedure improves the
robustness of our algorithm in terms of source identification. The HeViCS
catalogs contain about 52000, 42200, and 18700 sources selected at 250, 350,
and 500 micron above 3sigma and are ~ 75%, 62%, and 50% complete at flux
densities of 20 mJy at 250, 350, 500 micron, respectively. We then measured
source number counts at 250, 350, and 500 micron and we also cross-correlated
the catalogs with the Sloan Digital Sky Survey to investigate the redshift
distribution of the nearby sources. From this cross-correlation, we select
~2000 sources with reliable fluxes and a high signal-to-noise ratio, finding an
average redshift z~0.3+/-0.22. The number counts at 250, 350, and 500 micron
show an increase in the slope below 200 mJy, indicating a strong evolution in
number of density for galaxies at these fluxes. In general, models tend to
overpredict the counts at brighter flux densities, underlying the importance of
studying the Rayleigh-Jeans part of the spectral energy distribution to refine
the theoretical recipes of the models. Our iterative method for source
identification allowed the detection of a family of 500 micron sources that are
not foreground objects belonging to Virgo and not found in other catalogs.
