It's known to occur when an object is speeding away from us. Thus, the expanding universe was born. But he was careful not to assume that this was the only possible interpretation of the redshift data. Others since have thrown scientific caution to the winds and used Hubble's hypothesis as a rubbery yardstick with which to measure the size and age of the universe. Arp avoided this unscientific approach and made discoveries that are unequalled in the history of astronomy.
Many peculiar galaxies turn out to be what are known as active galaxies.
They are often seen to have thin jets of matter firing from their cores, and bridges of matter or radio lobes connecting them with nearby objects. Arp noticed that quasars are clustered in the sky with active galaxies far too often to be a coincidence. Quasars are faint starlike objects whose spectra are highly redshifted. The Big Bang view is that their redshifts are due to the expansion of the universe and the doppler effect as the quasars race away from us at a good fraction of light speed. A high redshift equates in that model to great distance so they should have no association with much closer galaxies.