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Submillimeter number counts at 250, 350 and 500 microns in BLAST data
Béthermin, M., Dole, H., Cousin, M., Bavouzet, N., submitted to AandA, 2010
BLAST (Balloon-borne Large-Aperture Submillimeter
Telescope) has performed the first deep and wide extragalactic
survey at 250, 350 and 500 um. The extragalactic number counts
at these wavelengths are important constraints for modeling the
infrared galaxies evolution.
We estimate the extragalactic number counts in the
BLAST data, allowing for a comparison with the results of the P(D)
analysis of Patanchon et al. (2009).
We use three methods to identify the submillimeter sources. 1) Blind
extraction using two different algorithms, wether the observed field
is confusion-limited or not. The photometry is computed with a new
simple and quick PSF fitting routine (FASTPHOT). We use Monte-Carlo
simulations (addition of artificial sources) to characterize the
efficiency of this extraction, and correct the flux boosting and the
Eddington bias. 2) Extraction with prior. We use the
Spitzer 24 um galaxies as a prior to probe slightly
fainter submillimeter flux densities. 3) A stacking
analysis of the Spitzer 24 um galaxies in the BLAST
data, to probe the peak of the differential submillimeter counts.
With the blind extraction, we reach 97, 83 and 76 mJy at resp. 250,
350 and 500 um with a 95\% completeness. With the prior
extraction, we reach 76 mJy (resp. 63 mJy) at resp. 250 um
(resp. 350 um). With the stacking analysis, we reach 6.2 mJy
(resp. 5.2 and 3.5 mJy) at 250 um (resp. 350 and
500 um). The differential submillimeter number counts are
derived, and start showing a turnover at flux densities decreasing
with increasing wavelength.
There is a very good agreement with the P(D) analysis of Patanchon
et al. (2009). At bright fluxes (>100 mJy), the Lagache et
al. (2004) and Le Borgne et al. (2009) models slightly overestimate
the observed counts, but there is a very good agreement near the
peak of differential number counts. Models predict that the galaxy
populations probed at the peak are likely z sim 1.8 ultra-luminous
infrared galaxies.
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