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We present an alternate origin scenario to explain the observed phenomena of(1) counter-rotation between different galaxy components and (2) the formationof ring galaxies. We suggest that these are direct consequences of the galaxybeing acted upon by a torque which causes a change in its primordial spinangular momentum first observed as changes in the gas kinematics ordistribution. We suggest that this torque is exerted by the gravitational forcebetween nearby galaxies. This origin requires the presence of at least onecompanion galaxy in the vicinity - we find a companion galaxy within 750 kpcfor 51/57 counter-rotating galaxies and literature indicates that all ringgalaxies have a companion galaxy thus giving observable credence to thisorigin. Moreover in these 51 galaxies, we find a kinematic offset betweenstellar and gas heliocentric velocities $>50$ kms$^{-1}$ for several galaxiesif the separation between the galaxies $<$ 100 kpc. This, we suggest, indicatesa change in the orbital angular momentum of the torqued galaxies. A majordifference between the torque origin suggested here and the existing model ofgas accretion/galaxy collision, generally used to explain the above twophenomena, is that the torque acts on the matter of the same galaxy whereas inthe latter case gas, with different properties, is brought in from outside. Animportant implication of our study is that mutual gravity torques acting on thegalaxy can explain the formation of warps, polar ring galaxies and lenticulargalaxies. We conclude that mutual gravity torques play an important role in thedynamical evolution of galaxies and that they naturally explain several galaxyobservables.

Torques and angular momentum: Counter-rotation in galaxies and ring galaxies