Number density of the measured DIB 18621 as a function of the Gaussian width (σ₈₆₂₁) and the central wavelength (λ₈₆₂₁) of the fit DIB profile for the full target sample (left), 8388 selected DIB measurements (middle), and the reliable measurements in AS23 (right). The color of the left panel represents the number of DIBs calculated in 0.025 A × 0.1 A bins. In the middle and right panels, the color represents the number density estimated by a Gaussian KDE. The dashed red line indicates the rest-frame wavelength of DIB λ8621 determined in this work (8623.141 Å, see Sect. 4.3).