Visualisation of a major merger process. We show characteristic parameters of the galaxy merger simulation of gSb + gSb with an orbit id 02dir and a merger inclination of 0° (see Sect. 4.1 and Table A.2). On the top panel, we show with a black line the distance between the COM of the two galaxies which corresponds to the distance between the two galaxies. The red line represents the half mass radius r_1/2 of the first galaxy. In order to illustrate the merger process, we show snapshots of only the gas at different merger stages. Black arrows indicate the exact stage of the merger process. On the second panel, we show the velocity difference between the two COM. On the third panel, we show the DP fraction which corresponds to the fraction of observation angles from which one detects a DP. On the bottom panels, we show zoomed-in observations of the central kiloparsecs of the first galaxy, we display, on the top panels, the 2D projection of the gas surface density Σ observed from a face-on view and the measured velocity dispersion σ on the panels beneath. To illustrate the gas dynamics, we show arrows representing the 2D projected in-plane velocity of the particles.