Hessian eigenvalues λ₋ (black) related to observed brightness temperatures at the nearest position. HI4PI data are indicated in blue and GASKAP-H I data in magenta. Critical points λ₋ < 0 are marked in red. Top: for the source J032548-735326 two absorption components (orange, scaled by a factor of 200) are indicated with an additional feature below the detection limit (arrow). For observational details see Fig. 8 of Nguyen et al. (2024). Bottom: the source J054427-715528 has a single absorption component (orange, scaled by a factor of 40). For observational details see Fig. 3 of Nguyen et al. (2024).