  Rotation curves constrain a galaxy's underlying mass density profile, under
the assumption that the observed rotation produces a centripetal force that
exactly balances the inward force of gravity. However, most rotation curves are
measured using emission lines from gas, which can experience additional forces
due to pressure. In realistic galaxy disks, the gas pressure declines with
radius, providing additional radial support to the disk. The measured
tangential rotation speed will therefore tend to lag the true circular velocity
of a test particle. The gas pressure is dominated by turbulence, and we
evaluate its likely amplitude from recent estimates of the gas velocity
dispersion and surface density. We show that where the amplitude of the
rotation curve is comparable to the characteristic velocities of the
interstellar turbulence, pressure support may lead to underestimates of the
mass density of the underlying dark matter halo and the inner slope of its
density profile. These effects may be significant for galaxies with rotation
speeds <75km/s, but are unlikely to be significant in higher mass galaxies. We
find that pressure support can be sustained over long timescales, because any
reduction in support due to the conversion of gas into stars is compensated for
by an inward flow of gas. However, we point to many uncertainties in assessing
the importance of pressure support in galaxies. Thus, while pressure support
may alleviate possible tensions between rotation curve observations and
LambdaCDM on kiloparsec scales, it should not be viewed as a definitive
solution at this time.
