4.2. Rotation-Dominated Pseudobulges
Figure 6, the
Vmax /
-
diagram
(Illingworth 1977;
Binney 1978a,
b),
shows that pseudobulges (filled
symbols) are more rotation-dominated than classical bulges (open symbols)
which are more rotation-dominated than giant ellipticals (crosses). This is
disky behavior, as follows. Seen edge-on, rotation-dominated disks have
parameters that approximately satisfy the extrapolation of the oblate
line to
0.8. Observed other than
edge-on, they project well above the
oblate line. In contrast, projection keeps
0.6
isotropic spheroids near the oblate line. The filled symbols therefore
represent objects that contain rapidly rotating and hence disky central
components. Of the most extreme cases, NGC 4736 is discussed in detail in
Kormendy & Kennicutt
(2004).
Complementary photometric evidence for pseudobulges in NGC 3945 and NGC 4371 is discussed in the next subsection.
![]() |
Figure 6. Relative importance of rotation
and velocity dispersion:
Vmax /
|