5 On a method to resolve the nuclear activity in galaxies Fig. 5.— Continuum levels under the emission line H α fitted with the sum of two exponential disks of scale lengths 0 . $^{′′}$7 and 4′′ and central intensity ratio 4/1, smoothed with the PSF. Fig. 6.— The PSF as derived from the star 150 ′′ West of NGC 1358. the slit (Fig. 6). The line of sight velocity, or redshift, of the central source and disk is an open question. Theureau et al. (1998) report a redshift of 4028 km s − $^{1}$, while Dumas et al. (2007) estimate the systemic redshift of the galaxy at 3997 ± 13 km s − $^{1}$. Rice et al. (2006) assume a system- atic redshift of 4008 km s − $^{1}$, and their spectrum (Fig. 4) shows a line of sight velocity of +145 km s − 1 for the stronger nuclear component with respect to the 4008 km s − 1 systemic velocity, i.e. a nuclear redshift of 4153 km s − 1 for the stronger component and 3939 km s − 1 for the blueshifted weaker component. We prefer to make the systemic velocity of the nuclear disk and the central emission source a free parameter in our model. The ad- ditional free parameters are the intensities of the central source and along the jet for each emission line. The fit of this preliminary model is given in Fig. A1. As can be seen, this model cannot reproduce the very sharp rise of the emission line velocity curves at the end of the jet about 2 ′′ to the East of the center. Thus, we feel forced to introduce a sharp shock at the end of the jet and a postshock cloud. b) In the potential of this bulge there is a rotating emission line disk. To avoid edge problems we as- sume this disk to be exponential and rotate with circular velocities. As the intensities of the disk is low compared to the other features, the exact scale length is not crucial, and we fix it ad hoc to 4 . $^{′′}$0. Then the only free parameters are the central surface line intensities of the emission line disk. c) A central emission line point source coinciding with the center 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 7 pixels (1 . $^{′′}$8) from the nucleus with constant line of sight velocity − 214 km s − 1 with respect to the point source, which was the velocity of the fainter component relative to the stronger as seen in the HST/STIS spectrum (Fig. 4). 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 a rotating exponential 4.2. Model 2 This model has the following features: The resulting intensities and velocities are convolved with the observed PSF as derived from a field star on Fig. 4.— [SII] λ 6716, 6731 spectrum from HST/STIS obser- vations of the nucleus of NGC 1358 (Rice et al. 2006), with con- strained Gaussian fits. In the bottom panel, the two components are separated by 214 km s − $^{1}$, and all densities are calculated as- suming 10000 K electron temperature. Unconstrained Gaussian fits result in almost identical fits.