longed to the two progenitor galaxies.

On the other hand, “young" stars form a stellar disk which is almost aligned with the orbital plane of the two progenitors. This young stellar disk is rotationally supported and strongly prograde-rotating, with a maximum velocity which is 4 times higher than the one of the “old stars". We also note a weak sign of counter-rotation in the central region of the disk, seen in the extracted stellar rotation curve.

Notably, stars that were initially part of the two progenitors’ bulges (“Pr.Bulge") are globally counter-rotating in the merger remnant, exhibiting almost a solid-body rotation.

One can also see the presence of two symmetrical off-centered peaks in the “all stars" stellar velocity dispersion map of Figure \[fig:figure1\]. This feature is commonly observed in ETGs with counter-rotating components (CRC). These galaxies are called “$2\sigma$-galaxies"[@Krajnovic_2011], and they were associated with external accretion of counter-rotating gas [@Rubin_1992] or major retrograde mergers [@Crocker_2009]. Here we see that a $2\sigma$-galaxy results from a single, prograde major merger. We also note that the $2\sigma$-feature is more prominent in the “all stars" map, where the young disk of stars is present, and less strong in the “old stars" map, even though the CRC is more prominent in the latter. In real ETGs a $2\sigma$-feature usually implicates the existence of a CRC, while the opposite is more ambiguous. Here we show that the $2\sigma$-feature might arise because of the presence of the CRC, but it is enhanced only if one of the components is fast-rotating[^2].

ORIGIN of the Kinematic Decoupling
==================================

In order to understand the origin of the kinematic decoupling in the central region of the galaxy, we study the behavior of the merging orbits of its two progenitors: Figure \[fig:figure3\] shows the separation (d) and the specific orbital angular momentum ($l_z$) for one of the two progenitors as a function of time. The mergi