## 4. Type dependence in the inverse magnitude TF relationAs will be discussed in Sect. 7.4, the type effect in the diameter
TF relation implies also a type effect in the magnitude relation,
though with a decreased amplitude. We checked this prediction with
those 4311 galaxies of our sample which also have For the common slope the value of 0.1 was adopted (Fig. 4, top panel). Bottom panels in Fig. 4 show the zero-points for the separate regressions and for the fixed slope. The latter ones we take as giving the actual zero-point shifts. It is satisfying to see that these, while following the shifts in the diameter relation, have a smaller amplitude as expected from the simple model of Sect. 7.4. We shall discuss the magnitude relation (both direct and inverse) in more detail elsewhere. Here it is sufficient to note that the slope 0.1 is also expected from the disc+bulge model similarly as the slope 0.5 for the diameter iTF relation.
The discussion above utilized galaxies at very different distances
(radial velocities). It is interesting to see if the type effect is
equally well seen for different radial velocities. To this end we have
calculated the cumulative averages of for each
type in restricted radial velocity ranges, where
is normalized using the inverse slope as
follows ( for diameters, for magnitudes The cumulative averages plotted in
Fig. 5 reveal clearly the zero-point shifts in the inverse
relations all along the velocity axis (note that the ordinate has been
put to zero for the complete sample for
© European Southern Observatory (ESO) 1997 Online publication: July 3, 1998 |