Figures 5 and
6 compare parameter correlations
for ellipticals, classical bulges, and pseudobulges. Sérsic
parameters of (pseudo)bulges are less accurate than those of Es, because
deriving them requires a decomposition of brightness profiles into
(pseudo)bulge and disk contributions. We have reduced leverage on bulge
parameters, and they are strongly coupled to the disk parameters.
Nevertheless, Figures 5 and
6 show that classical bulges are
indeed indistinguishable from elliptical galaxies, consistent with our
definition. Many pseudobulges are not very different, either; this is
one reason why they got confused with bulges. To find the difference
between pseudobulges and classical bulges, we need to look beyond
fundamental plane parameters and consider properties such as flattening
and V / 
.
Nevertheless, in Figures 5 and
6, pseudobulges also show larger
scatter than classical bulges, and they have smaller Sérsic
indices. Consistent with
Courteau et al. (1996),
MacArthur, Courteau,
& Holtzman (2003),
and the Carollo team papers,
Fisher & Drory
(2007a)
find a relatively clean separation between classical bulges with
n 
2
and pseudobulges (mostly) with n
2. Note that
this conclusion would not be clear if we believed that spheroidals are
faint ellipticals. In the above, the bulge-pseudobulge distinction is
based on morphological criteria listed in
KK04
and not on profile
shape. We do not understand galaxy formation well enough to predict
n for either type of bulge, but the distinction is clearcut
enough to be a classification aid.
Figure 6 shows that pseudobulges fade out by becoming low in density, not by becoming compact, like nuclear star clusters (black filled circles). This suggests that pseudobulges and nuclei are fundamentally different.