Physical Properties of the Gas in the Nuclear Regions of Nearby Dual AGN

Major galaxy mergers hosting two supermassive black holes (SMBHs) actively growing separated by less than 10 kpc, the so-called dual active galactic nuclei (AGNs) are ideal targets for understanding SMBH feeding, obscuration, and testing unification models and galaxy evolution. In this talk, I will present the main results from our program aimed to obtain optical and near-IR Integral Field Unit (IFU) spectroscopy and ALMA maps for a sample of confirmed nearby dual AGN. In addition to providing general properties of this population, I will focus on two remarkable systems, NGC6240 and Mrk 463.

At a distance of 210 Mpc, and a nuclear separation of ∼4 kpc, Mrk 463 is an excellent laboratory to study the gas dynamics, star formation processes and SMBH accretion in a late-stage gas-rich major galaxy merger. The optical data, which map the full extent of the merger, show evidence for a biconical outflow and material outflowing at >600 km/s, both associated with the east nucleus, along with large-scale gradients likely related to the ongoing galaxy merger. The ALMA observations of 12CO(2–1) and adjacent 1 mm continuum reveal the presence of ~1e9Mo in molecular gas in the system. The molecular gas shows velocity gradients of ~800 km/s and ~400 km/s around the Mrk 463E and 463W nuclei, respectively. We conclude that, in this system, the infall of ∼100s Mo/yr of molecular gas is in rough balance with the removal of ionized gas by a biconical outflow being fueled by a relatively small, <0.01% of accretion onto each SMBH.

We will further present the highest resolution maps of the merging galaxy system NGC6240, which hosts two SMBH growing simultaneously. At 0.03″ (15 pc), the ALMA 12CO(2-1) observations are a perfect match for existing Hubble optical and near-IR observations of this system. We find that most of the molecular gas is found in between the two nuclei but forming a clumpy stream and not a smooth rotating disk as it was previously assumed based on lower resolution data. A clear velocity gradient suggests that the molecular gas is getting ready for the next stage, in which will coalesce around each nuclei, being available significantly increase the amount of accretion onto each SMBH. We further detect the presence of significant high velocity, >500 km/s, outflows, responsible for the removal of a fraction of the material.

These results clearly show the importance of performing high resolution multi wavelength studies covering pc to kpc scales in order to understand the complex connection between black hole growth and galaxy evolution in this critical phase.