For our samples,
has been measured for 42 of the HydraI galaxies
and 113 of the Coma galaxies.
We test if the two samples follow the same
First we fit the two samples individually.
We compare the slopes and find a non-significant difference of
Second we fit the two samples together,
with the zero point for each sample left free.
We find a non-significant difference of
We conclude that the galaxies in the central parts of the
HydraI cluster and the Coma cluster follow the same
We then fit the two samples together and get
The slope that we find, , is in agreement with other studies in the literature: 0.175 (Burstein et al. 1988), 0.20 (Bender et al. 1993), (JFK96), and (J97). Note that the Bender et al. value is for all types of `dynamically hot galaxies' (DHGs), from dwarf spheroidals to giant ellipticals, with in the impressive range -8 to -24 mag. For comparison, our 155 galaxies fall in the categories `giant ellipticals' ( ; 66 galaxies), `intermediate ellipticals' ( < ; 88 galaxies), and `bright dwarf ellipticals' ( > ; 1 galaxy) in the classification scheme of Bender et al. A typical E/S0 color of was used.
We estimate the intrinsic scatter by subtracting the uncertainties on and (see Table ) in quadrature from . We find . A large part of the scatter is caused by the five very deviating galaxies, which are marked in Fig. . For all but D62, we have a possible explanation why they deviate, cf. the caption to the figure. If these five galaxies are omitted, the scatter decreases from 0.028 to 0.020. The latter value corresponds to . Bender et al. (1993) found for their DHG sample. depends on both age and metallicity. For the Vazdekis et al. (1996) models with a bi-modal IMF with high mass slope , the predictions can be approximated by (J97; Eq. ) for ages > 5 Gyr. If the intrinsic scatter ( ) in the - relation is due to scatter in age alone, the scatter in at a given is 0.20 dex (46% in age). If it is due to scatter in metallicity alone, the scatter in is 0.13 dex (30% in Z). These considerations are revisited in Sect. (p. ) in the light of the age-metallicity-sigma relation. Bender et al. (1993) found the allowed scatter in age or Z to be 15% for both. This value was based on their and different population synthesis models than the ones we use.
Properties of E and S0 Galaxies in the Clusters HydraI and Coma
Master's Thesis, University of Copenhagen, July 1997
Bo Milvang-Jensen (firstname.lastname@example.org)