Ring Galaxies Through Off-center Minor Collisions by Tuning Bulge-to-disk Mass Ratio of Progenitors

Abstract

Collisional ring galaxies (CRGs) are formed through off-center collisions between a target galaxy and an intruder dwarf galaxy. We study the mass distribution and kinematics of CRGs by tuning the bulge-to-disk mass ratio ( B / D ) for the progenitor; i.e., the target galaxy. We find that the lifetime of the ring correlates with the initial impact velocity vertical to the disk plane (i.e., v z 0 ). Three orbits for the collisional galaxy pair, on which clear and asymmetric rings form after collisions, are selected to perform the N -body simulations at different values of B / D for the progenitor. It is found that the ring structures are the strongest for CRGs with small values of B / D . The Sérsic index, n , of the central remnant in the target galaxy becomes larger after collision. Moreover, the Sérsic index of a central remnant strongly correlates with the initial value of B / D for the progenitor. A bulge-less progenitor results in a late-type object in the center of the ring galaxy, whereas a bulge-dominated progenitor leads to an early-type central remnant. Progenitors with B / D  ∈ [0.1, 0.3] (i.e., minor bulges) leave central remnants with n  ≈ 4. These results provide a possible explanation for the formation of a recently observed CRG with an early-type central nucleus, SDSS J1634+2049. In addition, we find that the radial and azimuthal velocity profiles for a ring galaxy are more sensitive to the B / D than the initial relative velocity of the progenitor.