Detection of non-ordered central gas motions in a sample of four low surface brightness galaxies

Aims: We present integral-field spectroscopy of the ionized gas in the central regions of four galaxies with a low surface brightness disk taken with the Visible Multi Object Spectrograph at the Very Large Telescope and aimed at testing the accuracy in the determination of the central logarithmic slope α of the mass density radial profile ρ(r)∝ r^α in this class of objects. Methods: For all the sample galaxies we subtracted the best-fit model of gas in circular motions from the observed velocity field and derived the residuals. Only ESO-LV5340200 is characterized by a regular velocity field. We extracted the velocity curves of this galaxy along several position angles, in order to estimate the uncertainty in deriving the central gradient of the total mass density from long-slit spectroscopy. Results: We report the detection of strong non-ordered motions of the ionized gas in three out of four sample galaxies. The deviations have velocity amplitudes and spatial scales that keep it from being possible to disentangle the cuspy and core density radial profiles.