We measured the stellar kinematics from the galaxy absorption features
present in the wavelength range and centered on the Mg line triplet
(
Å) by applying the Fourier
Correlation Quotient method (Bender 1990) as done by BSG94.
The spectra were rebinned along the dispersion direction to a natural
logarithmic scale, and along the spatial direction to obtain a nearly
constant
per resolution element. In a few spectra the
S/N decreases to
10 at the outermost radii. The galaxy
continuum was removed row-by-row by fitting a fourth to sixth order
polynomial.
The quality of the final spectrum depends on the resulting S/N. In Fig. 1 we show examples of central spectra covering the 3
quality classes listed in Table 1. The quality
parameter is 1 for
,
2 for
,
3 for
20
< S/N < 50.
![]() |
Figure 1: Examples of central spectra covering the range of quality classes. Relative fluxes have false zero points for viewing convenience. |
![]() |
Figure 3:
Kinematical parameters (v, ![]() ![]() |
To measure the stellar kinematics of the sample galaxies we adopted HR 6817 (K1III) as kinematical template for runs 1, 2 and 3 and HR 3427
(K0III) for run 4
and we considered the wavelength range 5115-5541 Å (see Fig. 1) around the Mg lines of the galaxies.
We derived for each galaxy spectrum the line-of-sight velocity
distribution (LOSVD) along the slit and measured its moments, namely
the radial velocity v, the velocity dispersion
and the
values of the coefficients H3 and H4. At each radius, they have
been derived by fitting the LOSVD with a Gaussian plus third- and
fourth-order Gauss-Hermite polynomials
and
,
which describe the asymmetric and symmetric deviations of the LOSVD
from a pure Gaussian profile (van der Marel & Franx 1993; Gerhard
1993).
Errors on the LOSVD moments were derived from photon statistics and
CCD read-out noise, calibrating them by Monte Carlo simulations as
done by BSG94. In general, errors are in the range of 3-10
for v and
,
and of 0.01-0.04 for H3 and H4, becoming
larger in the outer parts of some galaxies where for
.
These errors do not take into account possible systematic effects due
to template mismatch or the presence of dust and/or faint emission.
The measured stellar kinematics are reported in Table 3 and plotted in Fig. 2.
Figure 3 shows the comparison
between the measurements of v, ,
H3, and H4 along the
major axis of GMP 1176 and GMP 3792 obtained here and measurements
obtained in Paper I. The value derived from the different datasets are
in agreement within the errors. However in the case of GMP 3792 the
velocity dispersion measured in run 4 is systematically lower than
that measured both in Paper I and in run 1.
Copyright ESO 2002