A hidden molecular outflow in the LIRG Zw 049.057
  Feedback in the form of mass outflows driven by star formation or active
galactic nuclei is a key component of galaxy evolution. The luminous infrared
galaxy Zw 049.057 harbours a compact obscured nucleus with a possible far-IR
signature of outflowing molecular gas. Due to the high optical depths at far-IR
wavelengths, the interpretation of the outflow signature is uncertain. At mm
and radio wavelengths, the radiation is better able to penetrate the large
columns of gas and dust. We used high resolution observations from the SMA,
ALMA, and the VLA to image the CO 2-1 and 6-5 emission, the 690 GHz continuum,
the radio cm continuum, and absorptions by rotationally excited OH. The CO line
profiles exhibit wings extending 300 km/s beyond the systemic velocity. At cm
wavelengths, we find a compact (40 pc) continuum component in the nucleus, with
weaker emission extending several 100 pc approximately along the major and
minor axes of the galaxy. In the OH absorption lines toward the compact
continuum, wings extending to a similar velocity as for the CO are seen on the
blue side of the profile. The weak cm continuum emission along the minor axis
is aligned with a highly collimated, jet-like dust feature previously seen in
near-IR images of the galaxy. Comparison of the apparent optical depths in the
OH lines indicate that the excitation conditions in Zw 049.057 differ from
those in other OH megamaser galaxies. We interpret the wings in the spectral
lines as signatures of a molecular outflow. A relation between this outflow and
the minor axis radio feature is possible, although further studies are required
to investigate this possible association and understand the connection between
the outflow and the nuclear activity. Finally, we suggest that the differing OH
excitation conditions are further evidence that Zw 049.057 is in a transition
phase between megamaser and kilomaser activity.
