High resolution mapping of CO(1–0) in NGC 6240^{⋆, ⋆⋆}

¹ IRAM – Institut de RadioAstronomie Millimétrique, 300 rue de la Piscine, Domaine Universitaire, 38406 Saint-Martin d’Hères, France
e-mail: feruglio@iram.fr
² INAF – Osservatorio astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Italy
³ Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Ave., Cambridge CB3 0HE, UK
⁴ Max-Planck-Institut fur Extraterrestrische Physik (MPE), Giessenbachstr. 1, 85748 Garching, Germany

Received: 11 February 2013
Accepted: 1 July 2013

Abstract

We present long baseline CO(1–0) mapping of the luminous infrared galaxy NGC 6240 obtained with the IRAM - Plateau de Bure Interferometer. This source is a well known early-stage merging system hosting two active galactic nuclei (AGN). We find a broad CO(1−0) line profile with maximum velocity 800 km s^-1 and a total line width of 1400 km s^-1 that displays several kinematic components, revealing the complexity of the gas dynamics in this system. We detect a blueshifted CO emission with velocity between −200 and −500 km s^-1, which peaks around the southern AGN at the same position where the H₂ outflow is located. We interpret this blueshifted component as an outflow with a mass loss rate of ~500 M_⊙ yr^-1, originating from the southern nucleus. The spatial and spectral match strongly suggests that the CO outflow is connected to the H₂ superwind located around the southern AGN and to the large scale CO outflow with similar velocities extended on scales of ~10 kpc. The large mass loading factor (Ṁ/SFR ~ 10) of the molecular gas suggests that the outflow is likely driven by both SNa winds and the radiation of the southern AGN. We discovered a nuclear, redshifted CO emission peaking in the midpoint of the two nuclei, as is the case for the CO emission at the systemic velocity. The large velocity dispersion, which reaches its maximum (~500 km s^-1) in the midpoint between the two nuclei, suggests that the gas might be highly turbulent in this region, although the presence of an unresolved rotation component cannot be ruled out.