Top: noise map of the fully combined N₂H⁺ image (see text) in the G351.77 protocluster. The spectra with the highest noise values are located near the edges, as was expected. The mean rms value across the entire map is ~0.66 K, whereas the mean value in regions with S/N > 9 is ~0.40 K. Bottom: signal-to-noise ratio (S/N) map. Spectra with high S/N are distributed following filamentary structures. The contours show the areas where spectra with S/N ≥ 9 are found (see Appendix B). The ellipse in the bottom left corner represents the final beam size of the N₂H⁺ data of 2.3″ × 2.1″, or 4.6 kau × 4.2 kau.