Observed velocity (left panel) and velocity dispersion profiles (right panel) of A521 from the [O II] emission line (in green) and CO(4-3) line (in black). The solid line is the average rotation curve of the two counter-images. The curves are extracted from the observed data in the image plane, uncorrected for beam-smearing or inclination. The data cubes for CO and [O II] were convolved to the same spatial resolution of 0.69″ (∼2 − 3 kpc on average). The two dashed lines indicate the intrinsic velocity dispersion of 54 ± 11 km s⁻¹ and 11 ± 8 km s⁻¹ measured from the [O II] (in green) and CO (in black) velocity dispersion maps at large radii (R >  R_e when possible), respectively.