We carry out a blind search of 3 mm continuum sources using the ALMA Science Archive to derive the first galaxy number counts at this wavelength. The analyzed data are drawn from observations toward three extragalactic legacy fields: COSMOS, CDF-S, and the UDS comprising more than 130 individual ALMA Band 3 pointings and an effective survey area of ≈200 arcmin2 with a continuum sensitivity that allows for the direct detection of unlensed Dusty Star-forming Galaxies (DSFGs) dust emission beyond the epoch of reionization. We present a catalog of 16 sources detected at >5σ with flux densities from which number counts are derived. These number counts are then used to place constraints on the volume density of DSFGs with an empirical backward evolution model. Our measured 3 mm number counts indicate that the contribution of DSFGs to the cosmic star formation rate density at z??4 is non-negligible. This is contrary to the generally adopted assumption of a sharply decreasing contribution of obscured galaxies at z?>?4 as inferred by optical and near-infrared surveys. This work demonstrates the power of ALMA-3 mm observations, which can reach outstanding continuum sensitivities during typical spectral line science programs. Further constraints on 3 mm selected galaxies will be essential to refine models of galaxy formation and evolution as well as models of early universe dust production mechanisms.
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机译：我们使用ALMA科学档案库对3 mm连续体源进行盲搜索，以得出该波长下的第一个星系数计数。分析的数据来自对三个银河系外遗留场的观测数据：COSMOS，CDF-S和UDS，包含130多个单独的ALMA Band 3指向和有效的测量区域，≈200arcmin2，并具有连续灵敏度，可直接检测在电离时代以外的无透镜尘埃形成星系（DSFG）的尘埃排放。我们提出了一个目录，该目录包含在>5σ时检测到的16种源，它们的磁通密度可从中得出数量计数。这些数量的计数然后用于通过经验向后演化模型对DSFG的体积密度施加约束。我们测得的3毫米数计数表明，DSFG对z≤4时宇宙恒星形成速率密度的贡献不可忽略。这与通常采用的假设相反，即光学和近红外测量推断出，在z≥4时，模糊星系的贡献急剧下降。这项工作证明了ALMA-3 mm观测的强大功能，在典型的谱线科学计划中可以达到出色的连续谱灵敏度。对3mm选定星系的进一步限制对于完善星系形成和演化模型以及早期宇宙尘埃产生机制的模型至关重要。
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