emission line disk similar to the one in Model 1, again with a scale length of 4 . $^{′′}$0 and the only free parameters are the central surface line intensities. Lindblad et al. 6 c) A central emission line point source coinciding with the centra of the bulge and the emission line disk and at rest with respect to that center. d) A gas flow, here called the “jet”, seen from the nucleus out to a certain number of pixels from the nucleus, with constant line of sight velocity − 214 km s − 1 with respect to the point source. This again is the velocity of the fainter component relative to the stronger as seen in the HST/STIS spectrum (Fig. 4). In a chosen pixel at the end of the jet, we introduce a sharp shock, with a jump to more positive velocities, and in the following pixels, up to pixel 8, a postshock cloud with constant velocity. The mean velocity in the shock pixel is given some intermediate velocity between those of the jet and the postshock cloud. fit the velocities away from the center simultaneously on both sides, as can be seen in Fig. A2. Due to the jet, the observed velocities on the left side are more influenced by the inner part of the disk, and on the right side by the outer part. We can then introduce an asymmetry of the observations without abandoning the circular sym- metry of the disk by describing its surface intensity as the sum of two superposed exponential disks with widely different scale lengths and varying their central intensi- ties independently. This results in differences in the line ratios, simulating a gradient of these ratios within the disk. This leads us to the next model. This model is the final one which gives us the best fit to the observed velocities and intensities in the nuclear region of the galaxy. Its features are: The resulting intensities and velocities are convolved with the observed PSF as derived from a field star on the slit (Fig. 6). Still, in this way we have tried to keep the free pa- rameters to a minimum, and the free parameters of this model, to be fitted to the observations, are: 4.3. Model 3 a) A stellar bulge identical with the bulge in Model 1 presented above, where the total mass M × sin $^{2}$( i ) of the bulge is the only free parameter. b) In the potential of this bulge there is a rotating emission line disk. We assume the intensities in the disk to be the sum of two exponential disks with differing scale lengths. As the intensities of the disk are low compared to the other features, the exact scale lengths are not crucial, and we fix them ad hoc to 0 . $^{′′}$7 and 4 . $^{′′}$0 (only for historical reasons the same as for the bulge). Then the only free parameters are the central surface line intensities of the two disks (here called Disk 1 and Disk 2) representing the inner and outer part respectively of the emission line disk. 1. The total mass M × sin $^{2}$( i ) of the bulge. 2. The common redshift of the central point source and the center of the emission line disk. 3. The intensity of the central point source for each emission line. 4. The central intensity of the emission line disk for each emission line. 5. The pixel to contain the shock and the intensity and velocity in that pixel. 6. The intensities along the jet flow for each emission line. 7. The common velocity and the intensities in the postshock cloud for each emission line. c) A central emission line point source coinciding with the centra of the bulge and the emission line disk and at rest with respect to that center. d) A gas flow, here called the “jet”, seen from the nu- cleus out to a certain number of pixels from the nucleus, with constant line of sight velocity − 214 km s − 1 with respect to the point source. This again is the velocity of the fainter component relative to the stronger as seen in the HST/STIS spectrum (Fig. 4). At the end of this jet, at the border be- tween two pixels, we introduce a sharp shock, with a jump to more positive velocities, and in the fol- lowing pixels, up to pixel 7, a postshock cloud with constant velocity. 1. The total mass M × sin $^{2}$( i ) of the bulge. 2. The common redshift of the central point source and the center of the emission line disk. 3. The intensity of the central point source for each emission line. The resulting intensities and velocities are convolved with the observed PSF as derived from the field star on the slit (Fig. 6). The number of free parameters of this model is less than that of Model 2 and they are: Further, it can be seen from the observations that the emission lines have long faint wings on the Western (neg- ative) side, actually H α and [NII] stretching furthest and [OIII] having the shortest wing. The run of the H α and [NII] velocities on the West side show that the main in- tensities of this extended emission come from the rotating disk. This indicates an asymmetry in the emission line disk, and this makes it difficult with the present model to These parameters are varied until a reasonable fit to the observed velocities and intensities have been ob- tained. The fit is displayed in Fig. A2. The shock is placed within pixel 5 with the intermediate velocity of − 100 km s − $^{1}$. This determines the postshock cloud ve- locity to about +100 km s − $^{1}$. As can be seen in Fig. A2, the line intensities of [OIII] and the velocities in the jet are not perfectly fitted, and to place the shock short of pixel 5 makes the situation worse.