Fabry-Perot observations of the ionized gas in NGC 3938

The nearly face-on spiral galaxy NGC 3938 has been observed in the H-alpha line with the TAURUS II Fabry-Perot interferometer at the William Herschel Telescope in order to study the kinematics of the ionized gas. We are able to construct intensity, velocity and velocity dispersion maps for this gala xy. The rotation curve of the galaxy is calculated up to 4.5 radial scale l engths from the galactic centre. The residual velocity field shows very sma ll values with no systematic pattern. The mean velocity dispersion is appro ximately constant with radius at about 11 km s(-1) as previously reported f or the neutral and molecular gas. We have also studied the relation between intensity and velocity dispersion for the ionized gas. We have found that this distribution is compatible with a turbulent gas relaxing to a Kolmogor ov type turbulence as the stationary regime. The average dispersion varies with intensity as sigma proportional to I-1/8 although it becomes much stee per at higher intensities, for which the dispersion is kept almost constant at a value of about 19 km s(-1).