The Large-scale Interstellar Medium of SS 433/W50 Revisited

Abstract

With new high-resolution CO and H i data, we revisited the large-scale interstellar medium (ISM) environment toward the SS 433/W50 system. We find that two interesting molecular cloud (MC) concentrations, G39.315−1.155 and G40.331−4.302, are well aligned along the precession cone of SS 433 within a smaller opening angle of ∼±7°. The kinematic features of the two MCs at ∼73–84 km s −1 , as well as those of the corresponding atomic-gas counterparts, are consistent with the kinematic characteristics of SS 433. That is, the receding gas from SS 433 jet is probably responsible for the redshifted feature of G39.315−1.155 near the Galactic plane, and the approaching one may power the blueshifted gas of G40.331−4.302 toward the observer. Moreover, the H i emission at V LSR  ∼ 70–90 km s −1 displays the morphological resemblance with the radio nebula W50. We suggest that the V LSR  = 77 ± 5 km s −1 gas is physically associated with SS 433/W50, leading to a near kinematic distance of 4.9 ± 0.4 kpc for the system. The observed gas features, which are located outside the current radio boundaries of W50, are probably the fossil record of jet–ISM interactions at ∼10 5 years ago. The energetic jets of the unique microquasar have profound effects on its ISM environment, which may facilitate the formation of molecular gas on the timescale of ≲0.1 Myr for the ram pressure of ∼2 × 10 6 K cm −3 .