The Large-scale ISM of SS433/W50 Revisited
  With new high-resolution CO and HI 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 ~7deg. The kinematic features of the two MCs at
~73--84 km/s, 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 HI emission
at VLSR~70--90 km/s displays the morphological resemblance with the radio
nebula W50. We suggest that the VLSR=77\pm5 km/s gas is physically associated
with SS 433/W50, leading to a near kinematic distance of 4.9\pm0.4 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 ~2x10^6 K cm-3.
