Blazing trails: Microquasars as head-tail sources and the seeding of magnetized plasma into the ISM

Abstract

We discuss the dynamics of microquasar jets in the interstellar medium, with specific focus on the effects of the X-ray binaries' space velocity with respect to the local Galactic standard of rest. We argue that, during late stages in the evolution of large scale radio nebulae around microquasars, the ram pressure of the interstellar medium due to the microquasar's space velocity becomes important and that microquasars with high velocities form the Galactic equivalent of extragalactic head-tail sources, i.e., that they leave behind trails of stripped radio plasma. Because of their higher space velocities, low-mass X-ray binaries are more likely to leave trails than high-mass X-ray binaries. We show that the volume of radio plasma released by microquasars over the history of the Galaxy is comparable to the disk volume and argue that a fraction of a few percent of the radio plasma left behind by the X-ray binary is likely mixed with the neutral phases of the ISM before the plasma is removed from the disk by buoyancy. Because the formation of microquasars is an unavoidable by-product of star formation, and because they can travel far from their birth places, their activity likely has important consequences for the evolution of magnetic fields in forming galaxies. We show that radio emission from the plasma inside the trail should be detectable at low frequencies. We suggest that LMXBs with high detected proper motions like XTE J1118+480 will be the best candidates for such a search.