Galaxy Rotation Curves: Impact of Angle on Velocity and Shape

[TrickyDicky]

Usually spectral lines of spiral arms are corrected for the angle of the galaxy plane with respect to our line of sight to give a velocity curve. I guess this works except in the case when the galaxy is exactly "face-on" from our view (at 90 degrees angle from our line of sight) where no Doppler velocity can be measured overimposed to the cosmological redshift.
Does the angle between line of sight and galactic plane influence the shape of the curves?
For instance I have seen rotation curves of M33 which is not edge-on and the rotation curve is not flat in this case,but raises steadily. http://www.hep.shef.ac.uk/research/dm/images/rotationCurve.jpg
Anyone knows of some relation between galaxy angle wrt our line of sight and shape of the rotation curve?

 

[amarante]

I think that what you get is the projected rotation velocity, V_rot *sin(i) .