2016/05/31 by Nick Scoville, Lena Murchikova, Fabian Walter +20 · 1 citation
Physics and Astronomy · #astro-ph.GA
paper · pdf · doi:10.3847/1538-4357/836/1/66
ApJ in press
arxiv created 2017/02/07 · arxiv updated 2017/02/15
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\arcsec 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\rm 2.6mm ∼1) at λ= 2.6 mm with a dust brightness temperature ∼147 K. The column of ISM at this nucleus is \rm NH2 ≥ 2×1026 cm-2, corresponding to ∼900 gr cm-2. The East nucleus is more elongated with radial extent 0.3\arcsec 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 \msun. The intrinsic widths of the emission lines are Δ\rm v (FWHM) = 250 (West) and 120 (East) \kms. Given the very short dissipation timescales for turbulence (\lesssim105 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.