Panel a: CMD of the stars located in the Cetus-Palca selection box (blue rectangle in Fig. 12) overlaid with a 14 Gyr isochrone with a metallicity of [Fe/H] = −1.93 (in orange). The black plain polygon shows the location of the RGB stars with the region where Gaia is complete, while the region where Gaia is not complete is shown by the dashed line polygon. Panel b: luminosity function of the RGB used to estimate the stellar mass of the Cetus-Palca stream (in blue), with the area affected by the drop in completeness (in grey). The orange histogram shows the luminosity function of a 1.5 × 10⁶ M_⊙, [Fe/H] = −1.93, 14 Gyr-old RGB population following a Kroupa mass function.