SDSS-IV MaNGA: Kinematic Asymmetry as An Indicator of Galaxy Interaction
  in Paired Galaxies
  The interaction between galaxies is believed to be the main origin of the
peculiarities of galaxies, which disturbs not only the morphology but also
their kinematics. These disturbed and asymmetric features are the indicators of
galaxy interaction. We study the velocity field of the ionized gas of the
paired galaxies in the SDSS-IV MaNGA IFU survey. Using the kinemetry package,
we fit the velocity field of the ionized gas to quantify the degree of
kinematic asymmetry. We find that the star formation rate (SFR) of the paired
galaxies with high kinematic asymmetry is significantly enhanced even when the
projected separation between the pair members is quite large (dp~100 kpc). On
the contrary, no significant SFR enhancement is found for the paired galaxies
with low kinematic asymmetry even when their projected separation is small (dp
< 30 kpc). Moreover, we also find that the fraction of galaxies with high
kinematic asymmetry is much higher in close pairs (dp < 30 kpc) than those with
larger dp, which explains well the early statistical findings of the
significant SFR enhancement in close pairs. Our new findings illustrate that
the kinematic asymmetry is an excellent indicator of galaxy-galaxy interaction
strength, which helps us better understand the merging stage of the observed
galaxy pairs.
