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

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 the 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., $v_{z0}$). Three orbits for the collisional galaxy pair, on which clear and asymmetric rings form after collisions, are selected to perform the \textit{N}-body simulations at different values of $B/D$ for the progenitor. It is found that the ring structures are the strongest for the CRGs with small values of $B/D$. The S\'{e}rsic index, $n$, of the central remnant in the target galaxy becomes larger after collision. Moreover, the S\'{e}rsic 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 $B/D\in [0.1,~0.3]$ (i.e., minor bulges) leave central remnants with $n\approx 4$. 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.