Integrated line flux of H₂CO (combination of both transitions) vs. CN N = 2−1 (main group of hyperfine components). Color codes indicate detected vs. non-detected lines: blue for detection of both lines, red for detection of the x-axis line only (here CN), black for detection of the y-axis line only (here H₂CO), and green for non detections. The detection threshold is set at 3σ. For detected lines, the errorbars are 1σ. For non-detected lines, the limit is the 2σ value (best fit + 2σ), and the arrow length is 1σ. Sources in italics are those with known molecular outflows.