Comparison of optical (CaT) and near-IR (CO 2.29μm) σ◦

For luminous infrared galaxy (LIRG) mergers (left), velocity dispersion measured with CO (CO σ₀) is significantly lower than that measured with the Calcium II Triplet (CaT σ₀). For non-LIRG mergers and normal elliptical galaxies (middle and right), there is no meaningful difference between the two techniques.