The Molecular Gas in the NGC 6240 Merging Galaxy System at the Highest Spatial Resolution

We present the highest resolution — 15 pc (0.03″) — ALMA ¹²CO(2-1) and millimeter continuum maps, tracers of the molecular gas and dust, respectively, in the nearby merging galaxy system NGC 6240, that hosts two supermassive black hole growing simultaneously. These observations provide an excellent spatial match to existing Hubble optical and near-IR observations of this system. A significant molecular gas mass, ~9 × 10⁹ M_⊙, can be located in between the two nuclei, forming a clumpy stream kinematically dominated by turbulence, rather than a smooth rotating disk as previously assumed from lower resolution data.Evidence for rotation is seen in the gas surrounding the southern nucleus, but not the northern one. Dynamical shells can be seen, likely associated with nuclear supernovae remnants. We further detect the presence of significant high velocity outflows, some of them reaching velocities >500 km/s, affecting a significant fraction, ~11% of the molecular gas in the nuclear region. Inside the sphere of influence of the supermassive black holes we find molecular masses of 1.3 × 10⁸ M_⊙ and 3.5 × 10⁸ M_⊙ for the northern and southern nuclei respectively. We are thus directly imaging the reservoir of gas that can accrete onto each supermassive black hole. These new ALMA maps highlight the critical need for high resolution observations of the molecular gas in order to understand the feeding of supermassive black holes and its connection to galaxy evolution.

Support for this work has been provided by FONDECYT Regular 1160999, 1190818, CONICYT PIA ACT172033 and Basal CATA PFB-06/2007 and AFB170002 grants. This work was performed in part at the Aspen Center for Physics, which is supported by National Science Foundation grant PHY-1607611.