Notes. ULTRASAT specs are from Shvartzvald et al. (2024); GALEX specs are from Martin et al. (2005). The redshift range z_Lyα is computed for the Lyα line λ_Lyα = 1216 Å; other parts of the UV spectrum are shifted to different ranges. We indicate both the pixel scale L_pix and (in parenthesis) the effective scale of the pixels used in Sect. 4. The monopole J_νobs and the variance ${\sigma }_N^2$ are estimated using Eqs. (10) and (2), respectively.