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3 The galaxy sample

For the inner square degree of the Coma cluster we selected 27 early-type galaxies from the complete catalogue of JF94. E and S0 galaxies were selected separately accordingly to the following strategy:

For the outer region of the cluster (D $\geq$ 40') we selected all and 8 early type galaxies identified in Sect. 2 of this paper.

Table 1 lists all galaxies of the selected spectroscopic sample and their photometric properties. Numeros 1-27 correspond to the inner sample: The photometric total gunn r magnitude from JK94 is converted to Kron-Cousins $R_{\rm KC_{\rm T}}$ using $R_{\rm KC}$ = r - 0.35 (see Jørgensen 1994; J94). Additionally the seeing corrected values for the effective radius r$_{\rm e}$ and the mean surface brightness $\langle SB_{\rm e}\rangle$ inside $r_{\rm e}$ from Jørgensen et al. (1995a, JFK95a) are listed. Different to BM87's approach, JK94 derived the fourth cosine coefficients c4 normalized to the equivalent radius $r = \sqrt{ab}$ where a and bare the semi-major and -minor axes. Hence the relation between a4, which is normalized to the semi-major axis, and c4 is

 \begin{displaymath}
a_4 = c_4 \times \sqrt{1-\epsilon},
\end{displaymath} (2)

where a4, c4, and $\epsilon$ are the Fourier coefficients and the ellipticity at the current semi-major axis, respectively. Since JK94 only give the intensity weighted $\langle c_4\rangle $ values and the ellipticity $\epsilon _{r_{\rm e}}$ at $r_{\rm e}$ we could not derive the intensity weighted $\langle a_4 \rangle$ values by combining Eqs. (1, 2). Instead we converted the available $\langle c_4\rangle $ values into $\langle a_4 \rangle$ using the relation

 \begin{displaymath}
\langle a_4\rangle = \langle c_4\rangle \times \sqrt{1-\epsilon_{r_{\rm e}}},
\end{displaymath} (3)

which are listed in Table 1. For galaxies with $\epsilon$ = 0.1 to 0.8 and a4 = -0.8 to +0.9 we tested how well this conversion works. It turned out that the difference of $\langle a_4 \rangle$ derived by Eq. (3) on the one side and by combining Eqs. (1, 2) on the other side is smaller than 0.02% on the mean, which is much smaller than the typical error of $\langle a_4 \rangle$. $\epsilon _{r_{\rm e}}$ from JK94 and the galaxy type given from D80 are also given in Table 1. Numeros 28-35 of Table 1 correspond to the outer sample and contain the parameter derived in Sect. 2 for the 8 identified early-type galaxies.

Comparison with the catalogue of JF94 shows that our inner sample (Nos. 1-27 in Table 1) is complete to $R_{\rm KC_{\rm T}}=12.63~\mathrm{ mag}$ and 42% complete in the range $12.63~\mathrm{ mag}<R_{\rm KC_{\rm T}}<14.06~\mathrm{ mag}$ corresponding to a limiting absolute magnitude of MR>-21.73  mag (H0=50 Mpc/km s-1 and $cz_{\rm CMB}=7200$ km s-1). The outer sample (Nos. 28-35 in Table 1) is complete to $R_{\rm KC_{\rm T}}=13.21 ~\mathrm{ mag}$. The mean effective radius of the sample is $\langle R_{\rm e} \rangle=13.1''$, the average effective surface brightness $\langle SB_{\rm e}\rangle = 19.9$ mag/arcsec2, the mean ellipticity $\langle \epsilon \rangle = 0.32$; 40% of the galaxies have significant disky ( $a_4/a \geq +0.5$) isophotes on the mean, while only two objects (6%) have significant boxy ( $a_4/a \leq -0.5$) isophotes. The isophotes of the remaining 54% do not deviate significantly from pure ellipses. The sample spans 3.1 decades in cluster density. Figure 2 shows the histogram of galaxy types as a function of the projected cluster distance D. Figure 3 shows the magnitudes of the galaxies as a function of D.


   
Table 1: The galaxies of the sample: GMP No., the number from GMP83; DN, numbers from Dressler (1980, D80); D, distance from the cluster center ($\alpha $ = 12:57.3; $\delta $ = +28:14.4' (1950)) given by GMP83. Photometric parameter for object 1-27 (inner sample): $R_{\rm KC_{\rm T}}$, Kron-Cousin R band magnitude transformed from the Gunn r magnitudes quoted from JF94 using $R_{\rm KC_{\rm T}} = r_{\rm T} - 0.35$mag (see J94); $r_{\rm e}$ and $\langle SB_{\rm e}\rangle$, seeing corrected effective radius and mean surface brightness within $r_{\rm e}$ from JFK95a; $\langle a_4 \rangle$, luminosity weighted mean a4 parameter (defined by BM87) converted from the luminosity weighted mean $\langle c_4\rangle $ from JK94 as described in the text; $\epsilon _{r_{\rm e}}$, ellipticity derived at $r_{\rm e}$ from JF94; type, galaxy classification from D80. Photometric parameter for objects 28-35 (outer sample): $R_{\rm c_{\rm T}}$, Kron-Cousin R band magnitude; $r_{\rm e}$, $\langle SB_{\rm e}\rangle$, a4, $\epsilon _{r_{\rm e}}$ and type derived from the data described in Sect. 2. (${\ast }$) photometric zero point determined with HST V band surface photometry (Proposal ID: 5997). ( ${\triangle }$) photometric zero point determined with surface photometry from GMP83
No. GMP No. NGC/IC No. DN D $R_{\rm KC_{\rm T}}$ $r_{\rm e}$ $\langle SB_{\rm e}\rangle$ $\langle a_4 \rangle$ $\epsilon _{r_{\rm e}}$ Type
        [''] [mag] [''] [mag/arcsec2] [%]    
1 3329 NGC 4874 129 130.6 10.61 70.79 22.13 +0.1 0.141 D
2 2921 NGC 4889 148 304.8 10.64 33.88 20.64 -0.4 0.360 D
3 4928 NGC 4839 31 2528.4 11.45 29.51 21.18 $\pm$0 0.426 E/S0 (D)
4 4822 NGC 4841A 240 2533.4 11.78 17.87 20.39 -0.4 0.157 E
5 1750 NGC 4926 49 2111.2 12.27 10.96 19.79 -0.1 0.132 E
6 2390 IC 4051 143 927.7 12.34 15.56 21.02 $\pm$0 0.264 E
7 2795 NGC 4895 206 939.7 12.49 10.00 19.86 +0.9 0.599 S0
8 3792 NGC 4860 194 775.7 12.63 8.51 19.64 +0.2 0.161 E
9 2629 NGC 4896 232 1480.4 12.76 11.75 20.49 +0.7 0.424 S0
10 3561 NGC 4865 179 528.7 12.82 5.13 18.77 +0.6 0.429 S0
11 2000 NGC 4923 78 1480.8 12.86 8.51 19.88 +0.2 0.182 E
12 2413 - 230 1675.2 12.88 7.76 19.72 +0.5 0.405 S0
13 4829 NGC 4840 46 2184.3 12.93 6.46 19.35 +0.5 0.163 E/S0
14 3510 NGC 4869 105 359.6 12.93 7.59 19.75 +0.2 0.112 E
15 2417 NGC 4908 167 916.7 12.97 7.08 19.60 -0.2 0.322 S0/E
16 2440 IC 4045 168 945.9 13.24 4.37 18.79 +0.9 0.330 E
17 3414 NGC 4871 131 208.6 13.27 8.32 20.24 +1.1 0.410 S0
18 4315 NGC 4850 137 1104.0 13.36 4.68 19.07 +0.2 0.212 E/S0
19 3073 NGC 4883 175 271.4 13.36 6.91 19.91 +0.4 0.224 S0
20 1853 - 190 1674.6 13.45 4.27 18.96 +4.9 0.558 S0
21 3201 NGC 4876 124 210.2 13.51 5.13 19.47 $\pm$0 0.297 E
22 3661 - 13 2087.8 13.67 5.25 19.57 +0.3 0.264 S0
23 4679 - 75 1756.8 13.71 12.02 21.52 +2.6 0.789 S0
24 3352 NGC 4872 130 170.3 13.75 3.02 18.53 +0.6 0.054 E/S0
25 2535 IC 4041 145 742.0 13.81 7.41 20.52 +0.4 0.443 S0
26 3958 IC 3947 72 971.3 14.00 3.31 19.00 +1.6 0.323 E
27 2776 - 39 1567.4 14.06 5.76 20.25 +0.3 0.177 S0/E
28 0144 NGC 4957 - 4574.0 12.16$^{\ast}$ 18.44 20.38 +0.4 0.256 E
29 0282 NGC 4952 - 5849.3 12.03$^{\ast}$ 14.11 19.67 +0.9 0.315 E
30 0756 NGC 4944 - 33294 12.48 $^{\triangle}$ 11.68 19.71 +0.7 0.657 S0
31 1176 NGC 4931 - 2601.1 13.21 $^{\triangle}$ 7.40 19.45 +3.1 0.552 S0
32 1990 - - 4413.1 12.78 $^{\triangle}$ 9.45 19.55 -0.6 0.485 E/S0
33 5279 NGC 4827 - 3737.1 12.33$^{\ast}$ 13.61 19.90 +0.1 0.205 E
34 5568 NGC 4816 - 2937.6 11.50$^{\ast}$ 55.72 22.13 -0.1 0.284 S0
35 5975 NGC 4807 - 3764.5 12.89$^{\ast}$ 6.67 18.91 -0.8 0.170 E


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