There are two different kinematical components in the ellipticals with dust lanes. The first deals with the motions of the stars while the second deals with the gas associated with the dust. As listed in Table I, we possess information on the rotation and velocity dispersion for nine minor axis, one major axis, and two intermediate axis dust lane ellipticals. Data reduction is in progres for NGC 3302, NGC 4370, and NGC 5745 (Bertola et al. 1986).
The ionized gas has been detected in all but two minor axis dust lane ellipticals (Anon 0632-629 and Anon 0641-412). As a general result the rotation axis of the gas is perpendicular to that of the stars. This fact has deep implications on the origin of the gas and dust and gives strong support to the idea that they were acquired from outside. A recent and detailed study (Bland 1985) of the ionized gas in NGC 5128 leads to the conclusion that the mass of the gas is insignificant compared with the mass of the stellar component. At this point it should be mentioned that sixteen ellipticals in our sample were detected by the IRAS satellite. Dust mass estimates (Zeilinger 1986) from these data are in the range of 105 ÷ 106 M, so that the mass of the gas could be at least a couple of order of magnitudes larger. In this connection, an analysis on the possible self-gravitation of the dust rings in ellipticals similar to that for polar rings in S0 (Sparke 1986) is desirable.
Unfortunately no emission lines were detected in the only case of a major axis dust lane elliptical that has been studied (Anon 1029-459). If the gas is acquired from outside one would expect to find cases in which the gas is counter-rotating with respect to stars, as in NGC 7097 (Caldwell et al. 1986) and in NGC 4546 (Galletta 1986). From the data in Table I it appears immediately that no slow rotators relative to the isotropic oblate rotator are present among the dust lane ellipticals, although the brightest object reaches MB = -22.6. Whether this fact is due to the small sample at our disposal or is an intrinsic property of dust lane ellipticals, is a point to be checked with additional observations, in order to establish whether the nature of dust lane and normal ellipticals is similar or distinct.
It is worth noting that the rotational velocity of the major axis dust lane elliptical Anon 1029-459 is as high as 210 km sec-1, which is not reached in any other elliptical galaxy. This casts some doubt on whether ellipticals with dust lanes along the major axis, whose numbers have been so drastically reduced in our sample, really exist. This again is a point which needs future observations.
Considerable information on the intrinsic shape of the minor axis dust lane ellipticals can be deduced from kinematical observations. For a minor axis dust lane elliptical the pure oblate configuration is excluded. In fact in this case, if the gas is captured from outside it tends to align with the major axis in the inner regions (Lake and Norman 1983), causing a central discontinuity which is not observed. On the other hand the pure prolate configuration is also excluded in those cases with high values of Vmax / 0 due to the inability of the models to reproduce the case (Richstone and Potter 1982). Therefore it follows that the shape of a minor axis dust lane elliptical is the triaxial one. The rotational velocity which is observed along the major axis of the galaxies is a combination of the streaming velocity of the stars and of the tumbling around an axis in the plane defined by the minor and intermediate axis. In order to give rise to a well defined dust lane, the latter has see an almost stationary potential. Therefore the conclusion is that the tumbling motion, if any, has to be very small with respect to streaming. Some ideas as to whether we are looking closer to the intermediate axis or to the minor axis, can be derived by the amount of streaming which is higher in the first case than in the second. Then by means of the tensor virial theorem, a lower limit of the axial ratio b / a or c / a can be deduced. If warps are present in the dust lane, an upper limit to these axial ratios can be set by assuming that the warps show the direction of the original infall, on the hypothesis that the warps are transient phenomena (Caldwell 1984; Bertola et al. 1985).
Recent photometric studies of dust lane ellipticals concern NGC 5266 (Caldwell 1984, Varnas et al. 1986) and about twenty other cases whose reduction is in progress (Bertola et al. 1986). All cases are characterized by the fact that the r1/4 law is more or less followed. It seems that the photometry does not help so much in discriminating S0's from major axis dust lane ellipticals.