6 Comparison with literature

Kinematical radial profiles for the three cD galaxies GMP 3329 (NGC 4874), GMP 2921 (NGC 4889) and GMP 4928 (NGC 4839) have already been measured by Davies & Illingworth (1983), Davies & Birkinshaw (1988) and Fisher et al. (1995). Figures 7, 8 and 9 show the comparison with our profiles. No systematic differences are found inside the error bars, except for the center of GMP 2921 (NGC 4889), where the difference in spectral resolution and slit width could be responsible for the discrepancies observed.

Figure 7: The kinematical profile of GMP 3329 (NGC 4874) as measured during run 2 (spectral resolution $\sigma _{\rm inst}$ = 1.17 Å, filled triangles) compared to the data of Fisher et al. (1995, spectral resolution $\sigma _{\rm inst}$ = 2.77 Å, open squares). The data are folded with respect to the center and the same symbols are used for the two sides of the galaxies

Figure 8: The kinematical profiles of GMP 2921 (NGC 4889) as measured during run 2 (spectral resolution $\sigma _{\rm inst}$ = 1.17 Å, filled triangles) compared to the data of Fisher et al. (1995, spectral resolution $\sigma _{\rm inst}$ = 4.68 Å open squares) and the data of Davies & Illingworth (1983, spectral resolution $\sigma _{\rm inst}$ = 2.04 Å, open triangles). The data are folded with respect to the center and the same symbols are used for the two sides of the galaxies

Figure 9: The kinematical profiles of GMP 4928 (NGC 4839) as derived during runs 3 and 6 (spectral resolution $\sigma _{\rm inst}$ = 1.17 Å, filled squares) and those from run 2 (spectral resolution $\sigma _{\rm inst}$ = 1.17 Å, gray triangles) compared to the data of Fisher et al. (1995, spectral resolution $\sigma _{\rm inst}$ = 2.77 Å, open squares), the ones of Davies & Birkinshaw (1988, spectral resolution $\sigma _{\rm inst}$ = 5.11 Å, stars) and the ones of Davies & Illingworth (1983, spectral resolution $\sigma _{\rm inst}$ = 2.04 Å, open triangles). The data are folded with respect to the center and the same symbols are used for the two sides of the galaxies

We also compared our velocity dispersion with the aperture corrected mean values from J99. Therefore we derived the mean values of our presented $\sigma$-profiles within the "slit-equivalent'' radius (see Sect. 5). Figure 10 shows the difference between the mean values $\Delta (\log \sigma) = (\log \sigma)_{\mathrm{this work}}-(\log \sigma)_{\mathrm{J99}}$versus our measured mean values inside the standard aperture. The RMS scatter as well as the mean difference are listed No significant offset between the two datasets could be detected.

Radial line index profiles have been measured for the cD galaxies GMP 3329 (NGC 4874) and GMP 4928 (NGC 4839) by Fisher et al. (1995, FFI95) and Davies et al. (1993, DSP93). Figures 11 and 12 show the comparisons with our data. As FFI95 also derived the Mg₁ index for GMP 4928 (NGC 4839) and the C4668 index, for both galaxies we also measured these indices for these two galaxies for comparison reasons. The Mg indices compare well with previous works. Strong systematic differences of unclear origin are seen when considering the H$\beta$ profile of GMP 3329 (NGC 4874). The position angle of our observations at McD was the same as that used by FFI95. Hence the possibility of having investigated different areas of the galaxy can be ruled out as the reason. We also checked whether there is a systematic offset in our H$\beta$ index measured from the McD data. This could also be excluded since the H$\beta$profile for the second comparison galaxy GMP 4928 (NGC 4839) derived from the McD data is not only consistent with our CA data for this galaxy, but also with results from FFI95 and DSP93 (Fig. 12). Hence we conclude that there should also be no systematic error in the H$\beta$ index we derived for GMP 3329 (NGC 4874) from our McD data.

Figure 10: Comparison between the velocity dispersion measured from our data and the aperture corrected mean values from J99, within the circular standard aperture having a diameter of $2 r_{\rm A}$ = 3.4''. The "slit-equivalent'' radius $r_{\rm L}$ is 1.2'', 1.7'' and 2.5'' for the CA, McD, and MDM setup, respectively (see text). Filled triangles are the cD galaxies. $\Delta$ is calculated as "this work'' - "literature''

   

Table 4: Results from the comparisons of our mean data within the circular standard aperture (see text) with the mean values given by J99. $\Delta$ is calculated as "this work'' - "literature''. Listed are the mean and the rms of $\Delta$ as well as its mean error. (${\ast }$) - J99 lists Mg2 for all our 27 galaxies, but we could only derive reasonable radial profiles for the 8 galaxies observed during run 3 (see Sect. 4)

	N	$\langle \Delta \rangle$	rms $(\Delta)$	$\langle{\rm err}\rangle$
$\log\sigma$	27	0.017	0.039	0.028
Mgb	20	-0.08 Å	0.27 Å	0.25 Å
Mg2	8$^{\ast}$	0.005 mag	0.010 mag	0.008 mag
$\langle {\rm Fe}\rangle$	20	-0.11 Å	0.32 Å	0.22 Å
H$\beta$	26	-0.09 Å	0.35 Å	0.24 Å

Additionally the C4668 profile of GMP 4928 (NGC 4839) derived by FFI95 shows a small systematic difference to our profiles derived from CA as well as McD data.

Figure 11: The line index profiles of GMP 3329 (NGC 4874) as measured during run 2 (spectral resolution $\sigma _{\rm inst}$ = 1.17 Å, filled triangles) compared to the data of Fisher et al. (1995, spectral resolution $\sigma _{\rm inst}$ = 2.77 Å, open squared). The data are mean values for the two sides of the galaxies

Figure 12: The line index profiles of GMP 4928 (NGC 4839) as derived during runs 3 and 6 (spectral resolution $\sigma _{\rm inst}$ = 1.17 Å, filled squares) and those from run 2 (spectral resolution $\sigma _{\rm inst}$ = 1.17 Å, gray triangles) compared to the data of Fisher et al. (1995, spectral resolution $\sigma _{\rm inst}$ = 2.77 Å, open squares) and the ones of Davies et al. (1993, spectral resolution $\sigma _{\rm inst}$ = 5.11 Å, open triangles). The data are mean values for the two sides of the galaxies

We also compared our measured indices with the aperture corrected mean values from J99. Again we derived the mean values of our presented index-profiles within the "slit-equivalent'' radius (see Sect. 5). Figure 13 shows the difference between the mean values $\Delta$ index = index _{this work} - index _J99versus our measured mean values inside the standard aperture. The rms scatter as well as the mean differences are listed in Table 4. No significant offset between the two datasets could be detected.

Figure 13: Comparison between the line indices measured from our data and the aperture corrected mean values from J99, within the circular standard aperture having a diameter of $2 r_{\rm A}$ = 3.4''. The "slit-equivalent'' radius $r_{\rm L}$ is 1.2'', 1.7'' and 2.5'' for the CA, McD, and MDM setup, respectively (see text). Filled triangles are the cD galaxies. $\Delta$ is calculated as "this work'' - "literature''