Redshift source number density of SMGs at z ≳ 5. The black dot and arrow indicate a redshift source number density of z = 5.1–5.3 non-lensed SMGs with 1σ error, derived from known SMGs in the literature (HDF850.1, GN10, and AzTEC-3) and ASXDF1100.053.1, confirmed by this study. The curved lines show redshift source number density distribution from simulations and a photometric redshift study. The solid curve shows a prediction for F_1100 μm ≥ 3 mJy SMGs by Galform (Cowley et al. 2015). The dashed curve shows another prediction for F_1100 μm ≥ 3 SMGs by Hayward et al. (2013). Here the distribution is derived by applying the number of F_1100 μm ≥ 3 ALMA-identified AzTEC SMGs (Ikarashi et al. 2017a) to the prediction in the simulation for flux density closest to the F_1100 μm ≥ 3 criterion. The dotted curve shows a sum of redshift probability density for each AS2UDS SMGs with F_1100 μm ≥ 3 (Dudzevičiūtė et al. 2020).