Tides and Markarian Activity in Karachentsev Disk Galaxy Pairs

Abstract

Theories of nuclear activity mechanisms in disk galaxies range from internal (e.g., bars) to external (e.g., tidal perturbation by passing companions). The 1986–1987 simulation survey by Byrd and collaborators determined the tidal perturbation necessary to induce nuclear activity. We compare these simulations and theory with the observed Markarian activity in disk galaxy pairs in Karachentsev's 1983 list. For disk pairs, we derive the following tidal-hypothesis traits: (1) Compared with random association, there should be a numerical excess of pairs in which both galaxies are active, as well as a deficit of pairs with only one active member. There should be a small excess of pairs in which both are normal. (2) Nuclear activity will be preferentially excluded from pairs that are unequal and favorably distributed to pairs where the members are equal. (3) The product of velocity difference and separation in pairs where one or both members are active should be smaller than if both were normal. (4) The average size of pair members with one or both members active will be smaller than for pairs with both normal. A Monte Carlo match to the sample, assuming Keplerian orbits, reaches the same general conclusions as above. Observational surveys have raised doubts about the tidal explanation of Seyfert-type activity in galaxies, with some suggesting a weak or nonexistent correlation between nearby companions (tidal perturbation) and Seyfert activity as compared with a normal sample. The simulations show a several hundred million year delay in the appearance of activity after perturbation and a similar duration. Movement apart during delay and duration can explain these null results.