as the center galaxy of their galaxy group, which contains many dwarf galaxies (Ferguson and Sandage 1990; Tifft et al. 1975). Therefore, the differences in the abundance gradient could be explained by NGC 4636 experiencing fewer galaxy interactions leading to reduced diffusion of metals to the outer region. We consider this further in the next section.

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Metal-mass-to-light-ratio
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The gas mass distributions of NGC 4636 and NGC 1399 are shown in Figure 10, which also shows the Chandra results within 0.022 $r_{180}$ ($\simeq$ 15.6 kpc) (Fukazawa et al. 2006) and the ASCA results beyond this radius (Matsushita et al. 1998). These results show that the gas mass of NGC 4636 is about half as much as that of NGC 1399. This is possibly because NGC 1399 sits at the center of the Fornax cluster, where the potential is deeper than that for NGC 4636 (Figure 4), so the gas is more tightly bound by NGC 1399. The NGC 4636 metal mass distributions and metal-mass-to-light-ratios (MLR) of O and Fe are shown in Figures 11(a) and (b), respectively. The metal mass is obtained by multiplying the metal abundance value in the outermost region in Figure 5 with 