The surface density profiles from three different lines
of sight along each of the principal axes are measured by fitting
elliptical contours to the observed density map.
Figure 6
shows the log surface density 
plotted versus 
. Another
axis is included showing the equivalent surface brightness assuming
for the stars.
Figure 6: The surface brightness profile of the galaxy along
elliptical isophotes plotted versus for the principal axis
projections of the galaxy.
The simulated galaxy follows a deVaucouleurs law closely and would be
classified as a giant elliptical. A cD galaxy envelope did not form in
this simulation.
The nearly linear dependence on from 3-100 kpc reveal
that the galaxy follows a deVaucouleurs light profile. The profile is
similar to measured profiles of giant ellipticals (gE) rather than cD
galaxies which show an excess of light at large radii.
deVaucouleurs profiles are fit
for the effective radius, 
, and the total mass.
The effective radii (calculated as 
) is between 18-22 kpc
depending on the projection.
The fitted total mass is 
M
corresponding to a total luminosity of 6 
(assuming
and 
L).
The regularity of the isophotes and the measured scales and luminosities
of the merger remant are consistent with observations of giant elliptical
galaxies.
The 3-dimensional density profile of the merger remnant reveals the
relative distribution of stars and dark matter in an elliptical galaxy (Fig.
7). The Hernquist density profile (1990)[29],
provides convenient model
fits to both the stellar and dark matter profiles. The fitted masses and scale
radii are 
M and 
kpc for the stars
and 
M and 
kpc for the dark
matter as shown in Figure 7.
Figure 7: The spherically averaged density profile for the stars, dark
matter and the all of the matter. The Hernquist profile is fitted
separately to the stars and dark matter profile and the lines are shown.
The solid line is the sum of the two fits. The stellar density is about 3
times the dark matter density within 10 kpc or 0.5 and so central
kinematics are dominated by the observed stars.
Stellar mass dominates within r<10 kpc (
),
although the stellar density is only about 3 times the dark matter density
at the center.
The stellar and
dark matter density are equal in the range of 10-20 kpc (
)
while beyond 40 kpc (
) the dark matter density is at least ten times the
stellar density. The merging process tends to enhance the ratio of dark mass
to luminous mass within in the central regions. In the initial population
of disk+bulge galaxies the dark to luminous mass ratio at the half light
radius is 0.4, while the giant elliptical has a ratio of about 1.0 at a
nominal effective radius of 20 kpc, a factor of 2.5 enhancement.
The most likely reason for this enhancement is the tendency for disk stars
to be heated more effectively than the dark matter particles.
The same resonant interactions which create tidal tails during mergers
add energy more effectively to disk stars than to dark matter particles with
the same initial binding energy. The dark matter density may then be
enhanced slightly with respect to the stars in the merger remnant in
comparison to the initial disks.
The overall trend for increasing dark to luminous mass ratio is shown in
Figure 8. Stars dominate the central density
and the dark to luminous mass ratio is only about 0.3. At 
,
the ratio starts to grow linearly reaching 1.0 at 
continuing
to rise to 3.3 at 
. These mass ratios and general behaviour are
in accord with recent models of the dark matter in ellipticals derived from
combining surface brightness and kinematical information (e.g. Saglia et
al. 1992, 1993; Rix et al. 1997)[50][51][48].
Figure 8: The ratio of dark to luminous mass in the BCG over 5.
Dark mass still represents about 30% of the mass at the center in this
model. The ratio grows almost linearly with radius.