Astronomy and Astrophysics, volume 516, A43-43 (2010/6-2)
Submillimeter number counts at 250 µm, 350 µm and 500 µm in BLAST data.
BETHERMIN M., DOLE H., COUSIN M. and BAVOUZET N.
Abstract (from CDS):
The instrument BLAST (Balloon-borne Large-Aperture Submillimeter Telescope) performed the first deep and wide extragalactic survey at 250, 350 and 500µm. The extragalactic number counts at these wavelengths are important constraints for modeling the evolution of infrared galaxies. We estimate the extragalactic number counts in the BLAST data, which allow a comparison with the results of the P(D) analysis of Patanchon et al. (2009ApJ...707.1750P). We use three methods to identify the submillimeter sources. 1) Blind extraction using an algorithm when the observed field is confusion-limited and another one when the observed field is instrumental-noise-limited. The photometry is computed with a new simple and quick point spread function (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 using a prior. We use the Spitzer 24µm galaxies as a prior to probe slightly fainter submillimeter flux densities. 3) A stacking analysis of the Spitzer 24µm galaxies in the BLAST data to probe the peak of the differential submillimeter counts. With the blind extraction, we reach 97mJy, 83mJy and 76mJy at 250µm, 350µm and 500µm respectively with a 95% completeness. With the prior extraction, we reach 76mJy, 63mJy, 49mJy at 250µm, 350µm and 500µm respectively. With the stacking analysis, we reach 6.2mJy, 5.2mJy and 3.5mJy at 250µm, 350µm and 500µm respectively. 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. (2009ApJ...707.1750P). At bright fluxes (>100mJy), the Lagache et al. (2004ApJS..154..112L) and Le Borgne et al. (2009A&A...504..727L) models slightly overestimate the observed counts, but the data agree very well near the peak of the differential number counts. Models predict that the galaxy populations probed at the peak are likely z∼1.8 ultra-luminous infrared galaxies.