Submillimeter number counts at 250?μm, 350?μm and 500?μm in BLAST data

摘要

Context. The instrument BLAST (Balloon-borneLarge-Aperture Submillimeter Telescope) performed the first deep andwide extragalactic survey at 250, 350 and 500m. Theextragalactic number counts at these wavelengths are importantconstraints for modeling the evolution of infrared galaxies. Aims. We estimate the extragalactic number counts inthe BLAST data, which allow a comparison with the results of the P(D)analysis of Patanchon etal. (2009). Methods. We use three methods to identify thesubmillimeter sources. 1)Blind extraction using an algorithmwhen the observed field is confusion-limited and another one when theobserved field is instrumental-noise-limited. The photometry iscomputed with a new simple and quick point spread function (PSF)fitting routine (FASTPHOT). We use Monte-Carlo simulations (addition ofartificial sources) to characterize the efficiency of this extraction,and correct the flux boosting and the Eddington bias. 2) Extractionusing a prior. We use the Spitzer 24m galaxiesas a prior to probe slightly fainter submillimeter flux densities. 3) Astacking analysis of the Spitzer 24m galaxiesin the BLAST data to probe the peak of the differential submillimetercounts. Results. With the blind extraction, we reach97mJy, 83mJy and 76mJy at 250m,350mand 500mrespectively with a 95% completeness. With the prior extraction, wereach 76mJy, 63mJy, 49mJy at 250m,350mand 500mrespectively. With the stacking analysis, we reach 6.2mJy,5.2mJy and 3.5mJy at 250m,350mand 500mrespectively. The differential submillimeter number counts are derived,and start showing a turnover at flux densities decreasing withincreasing wavelength. Conclusions. There is a very good agreement with theP(D) analysis of Patanchon etal. (2009). At bright fluxes(>100mJy), the Lagache etal. (2004) andLeBorgne etal. (2009) models slightly overestimatethe observed counts, but the data agree very well near the peak of thedifferential number counts. Models predict that the galaxy populationsprobed at the peak are likely ultra-luminous infrared galaxies. Key words: cosmology: observations -galaxies: statistics - galaxies: evolution - galaxies: photometry -infrared: galaxies