Cold and warm molecular gas in the outflow of 4C 12.50

• Published in: Astronomy and astrophysics (Berlin) Vol. 541; p. L7
• Main Authors: Dasyra, K. M., Combes, F.
• Format: Journal Article
• Language: English
• Published: Les Ulis EDP Sciences 01.05.2012
• Subjects: Astronomy; Astrophysics; Earth, ocean, space; Exact sciences and technology; galaxies: active; galaxies: nuclei; infrared: galaxies; ISM: jets and outflows; ISM: kinematics and dynamics; line: profiles; Physics; Line shape; infrared: galaxies; ISM: kinematics and dynamics; Spatial observatory; Molecular gas; Column density; Continuum; Dynamics; galaxies: active; line: profiles; Kinematics; Galaxy nuclei; Mass ratio; Cosmic radio sources; Optical thickness; Excitation; galaxies: nuclei; Cold gas; ISM: jets and outflows; Radio galaxies; Molecular clouds; Molecular flow; Active galaxies; Upper bound; Jets; Infrared galaxies
• ISSN: 0004-6361; 1432-0746; 1432-0756
• DOI: 10.1051/0004-6361/201219229

We present deep observations of the 12CO (1−0) and (3−2) lines in the ultra-luminous infrared and radio galaxy 4C 12.50, carried out with the 30 m telescope of the Institut de Radioastronomie Millimétrique. 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-1 from systemic velocity with a central optical depth of 0.22. Its profile is similar to that of the  H i 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  ≥65 K 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 × 1022 cm-2. The outflow then carries an estimated cold  H2 mass of at least 4.2 × 103  M⊙ 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 × 109  M⊙, the outflow would most likely be seen in emission. Since the ambient cold gas reservoir of 4C 12.50 is 1.0 × 1010  M⊙, the outflowing-to-ambient mass ratio of the warm gas (37%) could be elevated with respect to that of the cold gas.