Cold and warm molecular gas in the outflow of 4C12.50
  We present deep observations of the 12CO(1-0) and (3-2) lines in the
ultra-luminous infrared and radio galaxy 4C12.50, carried out with the 30m
telescope of the Institut de Radioastronomie Millimetrique. Our observations
reveal the cold molecular gas component of a warm molecular gas outflow that
was previously known from Spitzer Space Telescope data. The 12CO(3-2) profile
indicates the presence of absorption at -950 km/s from systemic velocity with a
central optical depth of 0.22. Its profile is similar to that of the HI
absorption that was seen in radio data of this source. A potential detection of
the (0-1) absorption enabled us to place an upper limit of 0.03 on its central
optical depth, and to constrain the excitation temperature of the outflowing CO
gas to >=65K assuming that the gas is thermalized. If the molecular clouds
fully obscure the background millimeter continuum that is emitted by the radio
core, the H2 column density is >=1.8*10^22 /cm^2. The outflow then carries an
estimated cold H2 mass of at least 4.2*10^3 M_sun along the nuclear line of
sight. This mass will be even higher when integrated over several lines of
sight, but if it were to exceed 3*10^9 M_sun, the outflow would most likely be
seen in emission. Since the ambient cold gas reservoir of 4C12.50 is 1.0*10^10
M_sun, the outflowing-to-ambient mass ratio of the warm gas (37%) could be
elevated with respect to that of the cold gas.
