ALMA Resolves the Nuclear Disks of Arp 220

الأصل · EN

We present 90 mas (37 pc) resolution ALMA imaging of Arp 220 in the CO (1-0) line and continuum at λ= 2.6 mm. The internal gas distribution and kinematics of both galactic nuclei are well-resolved for the first time. In the West nucleus, the major gas and dust emission extends out to 0.2 radius (74 pc); the central resolution element shows a strong peak in the dust emission but a factor 3 dip in the CO line emission. In this nucleus, the dust is apparently optically thick (τ 2.6mm 1) at λ= 2.6 mm with a dust brightness temperature 147 K. The column of ISM at this nucleus is Nₕ₂ ≥ 2×10²⁶ cm⁻², corresponding to 900 gr cm⁻². The East nucleus is more elongated with radial extent 0.3 or 111 pc. The derived kinematics of the nuclear disks provide a good fit to the line profiles, yielding the emissivity distributions, the rotation curves and velocity dispersions. In the West nucleus, there is evidence of a central Keplerian component requiring a central mass of 8×10⁸. The intrinsic widths of the emission lines are Δ v (FWHM) = 250 (West) and 120 (East). Given the very short dissipation timescales for turbulence (10⁵ yrs), we suggest that the line widths may be due to semi-coherent motions within the nuclear disks. The symmetry of the nuclear disk structures is impressive -- implying the merger timescale is significantly longer than the rotation period of the disks.