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., vz0). 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.