Massive accretion disks

Recent high resolution near infrared (HST-NICMOS) and mm-interferometric imaging have revealed dense gas and dust accretion disks in nearby ultra-luminous galactic nuclei. In the best studied ultraluminousIR galaxy, Arp 220, the 2μm imaging shows dust disks in both of the merging galactic nuclei and mm-CO line imaging indicates molecular gasmasses ∼ 10⁹M⊙ for each disk. The two gas disks in Arp 220 are counterrotating and their dynamical masses are ∼ 2×10⁹ M⊙, that is, only slightly largerthan the gas masses. These disks have radii ∼100 pc and thickness 10-50 pc. The high brightness temperatures of the CO lines indicatethat the gas in the disks has area filling factors ∼25-50% and mean densitiesof ≥ 10⁴ cm⁻³. Within these nuclear disks, the rate of massive star formation is undoubtedly prodigious and, given the high viscosity of the gas, there will also be high radial accretion rates, perhaps ≥ 10 M⊙ yr ⁻¹. If this inflow persists to very small radii, it is enough to feed even the highest luminosity AGNs.