Title: Effects of global gas flows on type I migration,
Abstract: Magnetically-driven disk winds would alter the surface density slope of gas
in the inner region of a protoplanetary disk $(r \lesssim 1 {\rm au})$. This in
turn affects planet formation. Recently, the effect of disk wind torque has
been considered with the suggestion that it would carve out the surface density
of the disk from inside and would induce global gas flows (wind-driven
accretion). We aim to investigate effects of global gas flows on type I
migration and also examine planet formation. A simplified approach was taken to
address this issue, and N-body simulations with isolation-mass planets were
also performed. In previous studies, the effect of gas flow induced by
turbulence-driven accretion has been taken into account for its desaturation
effect of the corotation torque. If more rapid gas flows (e.g., wind-driven
accretion) are considered, the desaturation effect can be modified. In
MRI-inactive disks, in which the wind-driven accretion dominates the disk
evolution, the gas flow at the midplane plays an important role. If this flow
is fast, the corotation torque is efficiently desaturated. Then, the fact that
the surface density slope can be positive in the inner region due to the wind
torque can generate an outward migration region extended to super-Earth mass
planets. In this case, we observe that no planets fall onto the central star in
N-body simulations with migration forces imposed to reproduce such migration
pattern. We also see that super-Earth mass planets can undergo outward
migration. Relatively rapid gas flows affects type I migration and thus the
formation of close-in planets.