Astrophysical Tests of Modified Gravity: Stellar and Gaseous Rotation
  Curves in Dwarf Galaxies
  Chameleon theories of gravity predict that the gaseous component of isolated
dwarf galaxies rotates with a faster velocity than the stellar component. In
this paper, we exploit this effect to obtain new constraints on the model
parameters using the measured rotation curves of six low surface brightness
galaxies. For $f(R)$ theories, we rule out values of $f_{R0}>10^{-6}$. For more
general theories, we find that the constraints from Cepheid variable stars are
currently more competitive than the bounds we obtain here but we are able to
rule out self-screening parameters $\chi_c>10^{-6}$ for fifth-force strengths
(coupling of the scalar to matter) as low as $0.05$ the Newtonian force. This
region of parameter space has hitherto been inaccessible to astrophysical
probes. We discuss the future prospects for improving these bounds.
