Observations and reductions

We have obtained a total of 14 long-slit optical spectra in 10 different orientations and positions (see Figure ). Journal of spectroscopic observations is given in Table . Low-intermediate resolution spectra (FWHM=6Å in the light of H$\alpha$) with dispersion 2.65Å/pixel were obtained with the Boller & Chivens spectrograph at the Cassegrain focus of the 2.2-m telescope at Calar Alto (Almería, Spain) in January 1993. We used a 1024$\times$1024 Tek 24$\mu$m CCD. High resolution spectra (FWHM=0.9Å in H$\alpha$ and 0.39Å/pixel; slits #7R, #8R and #9R) were obtained using the IDS instrument at the Isaac Newton Telescope (INT) of the Observatorio del Roque de los Muchachos (La Palma, Spain) in January 1998. The detector was a 1024$\times$1024 Tek 24$\mu$m CCD. The spectra were reduced, wavelength and flux calibrated, using standard FIGARO (January 1993) and IRAF procedures (January 1998), and making use of the corresponding standard stars and lamp calibration spectra. Line fluxes were measured using the IRAF task SPLOT, obtaining errors lower than 15 per cent.

 

Table: Velocity gradients. $\omega_{\mathrm{0}}$ are the velocity gradients measured along the slits, meanwhile $\omega$ are the values projected to PA=12. Distances along the rotation axis, d, have been measured relative to the r-band outer isophotes centre. The central value has been estimated from the interpolated 2D velocity map.

d (kpc)	$\omega_{\mathrm{0}}$ (kms-1kpc-1)	$\omega$ (kms-1kpc-1)	Slit
	Steep/flat comp.	Steep/flat comp.
1.03	55$\pm$4/8$\pm$3	56$\pm$5/8$\pm$3	#9R
0.85	69$\pm$5/18$\pm$2	70$\pm$5/19$\pm$2	#7R
0.73	21$\pm$4	21$\pm$4	#2r
0.73	22$\pm$5	22$\pm$5	#2b
0.00		34$\pm$5
-0.12	33$\pm$4	33$\pm$4	#4r

We have also obtained B, V, r and K-band images in different observing runs as described in Table . Gunn-r band image was obtained at the 2.2-m telescope at Calar Alto in February 1992 with a GEC CCD with 800$\times$1156 30$\mu$m pixels. The Johnson-V band image was obtained at the 1.52m telescope at Calar Alto in December 1993 with a 1024$\times$1024 19$\mu$m pixels CCD. B band image was obtained at the 1-m Jacobus Kapteyn Telescope (JKT) at the Observatorio del Roque de los Muchachos in November 1997 with a 24$\mu$m 1024$\times$1024 pixels Tek CCD. Finally, the near-infrared K-band image was obtained at the 3.8-m UKIRT telescope at Mauna Kea observatory in April 1993. We used the 62$\times$58 InSb array camera IRCAM. Broad band images were reduced using standard MIDAS and IRAF procedures. The procedures described by Aragón-Salamanca et al. alfonso were employed for the reduction of the K-band near-infrared image. All the broad-band images were calibrated observing standard stars at different airmasses.

Additional narrow-band images were secured for us during service time at the 2.5-m Isaac Newton Telescope at the Observatorio del Roque de los Muchachos in December 1993. The detector was an EEV CCD with 1280$\times$1180 22.5$\mu$m pixels. [OIII]5007Å ( $\lambda_{\mathrm{0}}$=5014Å; FWHM=50Å) and on/off H$\alpha$ ( $\lambda_{\mathrm{0}}^{\mathrm{on}}$=6556Å, FWHM=60Å; $\lambda_{\mathrm{0}}^{\mathrm{off}}$=6607Å, FWHM=53Å) images were obtained. The continuum subtraction was performed using, respectively for [OIII] and H$\alpha$, the V-band and off-H$\alpha$ images.

The [OIII] and H$\alpha$ images were flux calibrated as follows. First, we convolved the b (blue-arm; see Table ) spectra with the [OIII] filter and the r (red-arm) spectra with the H$\alpha$ filter (see Table  & Figure ). Then, we collapsed these spectra in wavelength, obtaining the flux calibrated spatial profile of the [OIII] and H$\alpha$ emission. Now, we cropped and averaged in the [OIII] and H$\alpha$ images those regions covered by the b and r slits, obtaining the [OIII] and H$\alpha$ spatial profiles given by the images. Comparing these spatial profiles with those obtained from the spectra we calibrated both the [OIII] and H$\alpha$ images. Finally, these calibration relations were corrected for the sensitivity of the filters at the corresponding wavelength and, in the case of the H$\alpha$ emission, from the contribution of the [NII]6548Å and 6583Å lines. The reliability of this method was demonstrated after applying it to all the blue-arm and red-arm spectra, obtaining similar results within an error of 10 per cent.