Galaxy cluster CLJ1001 at z = 2.51 and the four member galaxies. Left: sky distributions of member galaxies around the cluster center. Red circles mark the two SBs and two MSs with the brightest CO(3−2) luminosities (S/N ≫ 10; S/N ∼ 30 for the two SBs) among all CO(3−2) detections (golden squares) in the central region of the cluster. The background is the K_s-band image from the UltraVista survey with a size of 70″ × 70″. The white cross shows the cluster center. The scale bar indicates half of the virial radius (R_200c ∼ 340 kpc) of the cluster. The large green circle denotes the ALMA FOV, corresponding to FWHP ∼53″ of the ALMA antennas’ primary beam at 98.63 GHz. Middle: velocity-integrated intensity map (Moment 0) of CO(3−2) (golden contours) detected by ALMA overlaid on the HST/F160W image of the two SBs and two MSs. Each panel is 2.5″ × 2.5″. The angular resolution is 0.31″ × 0.25″ (gray-filled ellipse in the bottom-left corner). The contour levels start at ±3σ and increase in steps of ±3σ, where positive and negative contours are solid and dashed, respectively. The red cross in each panel denotes the centroid of the stellar emission determined from the HST/F160W image. The derived integrated fluxes are presented in Table 1. Right: CO(3−2) line spectra of the four member galaxies. The CO lines are binned at 90 km s⁻¹, and the velocity range is shaded in green over which Moment 0 maps are integrated. The best-fit single Gaussian profiles are overlaid in red.