Fig. 1: Geometry of the DF2 and DF4 system.
From: A trail of dark-matter-free galaxies from a bullet-dwarf collision
a, The radial velocity difference between DF2 and DF4 is 358 km s−1 and this large velocity difference is accompanied by a large line-of-sight separation of 2.1 ± 0.5 Mpc (refs. 15,16). The geometry implies that the galaxies are moving away from each other. Tracing their positions back in time, we infer that they were formed in a high-speed encounter ≥6 Gyr ago. b, Example of a collisional scenario involving NGC 1052. Velocities are given with respect to that galaxy (cz = 1,488 km s−1). An infalling gas-rich galaxy on an unbound orbit collided with a satellite of NGC 1052 about 8 Gyr ago, leading to two dark remnants (possibly RCP 32 and DF7), DF2 and DF4, and three to seven other dark-matter-free galaxies.
