ALMA Lensing Cluster Survey: Deep 1.2 mm Number Counts and Infrared Luminosity Functions at z≃1-8

We present a statistical study of 180 dust continuum sources identified in 33 massive cluster fields by the ALMA Lensing Cluster Survey (ALCS) over a total of 133 arcmin^2 area, homogeneously observed at 1.2 mm. ALCS enables us to detect extremely faint mm sources by lensing magnification, including near-infrared (NIR) dark objects showing no counterparts in existing Hubble Space Telescope and Spitzer images. The dust continuum sources belong to a blind sample (N=141) with S/N ≳ 5.0 (a purity of > 0.99) or a secondary sample (N=39) with S/N= 4.0-5.0 screened by priors. With the blind sample, we securely derive 1.2-mm number counts down to ∼7 μJy, and find that the total integrated 1.2mm flux is 20.7^+8.5_-6.5 Jy deg^-2, resolving ≃ 80 The resolved fraction varies by a factor of 0.6-1.1 due to the completeness correction depending on the spatial size of the mm emission. We also derive infrared (IR) luminosity functions (LFs) at z=0.6-7.5 with the 1/V_ max method, finding the redshift evolution of IR LFs characterized by positive luminosity and negative density evolution. The total (=UV+IR) cosmic star-formation rate density (SFRD) at z>4 is estimated to be 161^+25_-21 exclusively based on optical-NIR surveys. Although our general understanding of the cosmic SFRD is unlikely to change beyond a factor of 2, these results add to the weight of evidence for an additional (≈ 60 contributed by the faint-mm population, including NIR dark objects.