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tokens: rot / σ profiles tend to peak at a median radius of R ∼ 3 R e . By comparison, the ePN.S FRs tend to peak at smaller fractions of R e , at a median 1.3 R e . This difference between the observed and simulated FRs is not a consequence of the selection functions of the samples. The TNG galaxies are selected according to color, mass and intermediate to major axis ratio p . The selection in p removes centrally elongated galaxies, most of which have intermediate to low λ (1 R e ) (Fig. 5 ). The Atlas3D sample, selected as described in Sect. 3 , has some of the disk galaxies removed which as in MANGA (Fig. 5 ) will be mostly located at high λ (1 R e ). We recall that in the comparison we consistently matched the color selection and mass range of the Atlas3D sample to the selection criteria adopted for the TNG galaxies. Thus the TNG sample should in principle contain a larger number of late type galaxies with strong disks, i.e. high V rot / σ , by comparison with Atlas3D. Figure 13 shows instead that the TNG100 and TNG50 ETG samples lack galaxies with high rotational support at 1 R e . In Sect. 6.1 we discussed that the effective radii used to normalize the radial scales in TNG would be expected to be systematically slightly overestimated compared to the observed R e since they are defined using the total bound stellar mass which is often inaccessible in observations. If taken into account, this effect would increase the gap between simulated and observed samples. On the other hand, since the mass-size relation is roughly reproduced in the simulations (Fig. 7 ), the different steepness of the V rot / σ profiles in observations and simulations implies a different distribution of the angular momentum as a function of radius in the simulated galaxies. This could be due to a too efficient condensation of the gas into stars that does not allow the gas to dissipate and collapse to small enough radii. 7.3. Simulated versus observed profiles – outskirts Figure 14 compares the relation between V rot / σ in the central regions and V rot / σ in the stellar halos for the simulated and observed galaxies. The observed galaxies are from the ePN.S survey ( Pulsoni et al. 2018 , their Fig. 9) and are reported in the top left panel. Their measurements use absorption line data at 1 R e and PN data for the halos, which on average cover 6 R e with a large scatter (minimum 3 R e , maximum 13 R e ). The central and right top panels show V rot / σ (6 R e ) versus V rot / σ (1 R e ) for TNG100 and TNG50 ETGs, respectively. Galaxies close to the dashed 1:1 lines show similar rotational support in the central regions and in the outskirts; galaxies below the lines have increased rotational support in their stellar halos; galaxies above the lines instead have reduced rotation at large radii. Fig. 14. V / σ ratio in the central regions compared with the V / σ at large radii. Top : V / σ (1 R e ) versus V / σ (6 R e ) for the ePN.S galaxies ( left ), TNG100 ( middle ), and TNG50 (