Panel (a): 1.3 mm continuum image of the W51 North region with a full uv range. The red ellipse is given by Gaussian fitting toward W51 North. This ellipse has been adopted as a model to perform ALMA simulations. Panel (b): Simulated full uv-range continuum image without any embedded source. Panel (c): Simulated uv-range constrained (> 910 kλ) continuum image without any embedded sources. Panel (d): Simulated full uv-range continuum image with two point sources. Panel (e): Simulated uv-range constrained (> 910 kλ) continuum image with two point sources. The contour levels in all the panels start from 12σ (1.32 mJy beam⁻¹). The residual map of the 1.3 mm continuum image generated by the TCLEAN task of CASA has been added to the simulated images to realistically simulate the noise.