We present ALMA 2-mm continuum and CO ( 2-1 ) spectral line imaging of the gravitationally lensed z = 0.654 star-forming/quasar composite RX J1131 - 1231 at 240 to 400 mas angular resolution .
The continuum emission is found to be compact and coincident with the optical emission , whereas the molecular gas forms a complete Einstein ring , which shows strong differential magnification .
The de-lensed source structure is determined on 400-parsec-scales resolution using a Bayesian pixelated visibility-fitting lens modelling technique .
The reconstructed molecular gas velocity-field is consistent with a large rotating disk with a major-axis FWHM \sim 9.4 kpc at an inclination angle of i = 54 ^ { \circ } and with a maximum rotational velocity of 280 km s ^ { -1 } .
From dynamical model fitting we find an enclosed mass within 5 kpc of M ( r < 5 ~ { } { kpc } ) = ( 1.46 \pm 0.31 ) \times 10 ^ { 11 } M _ { \odot } .
The molecular gas distribution is highly structured , with clumps that are co-incident with higher gas velocity dispersion regions ( 40–50 km s ^ { -1 } ) and with the intensity peaks in the optical emission , which are associated with sites of on-going turbulent star-formation .
The peak in the CO ( 2-1 ) distribution is not co-incident with the AGN , where there is a paucity of molecular gas emission , possibly due to radiative feedback from the central engine .
The intrinsic molecular gas luminosity is L ^ { \prime } _ { CO } = 1.2 \pm 0.3 \times 10 ^ { 10 } K km s ^ { -1 } pc ^ { 2 } and the inferred gas mass is M _ { H _ { 2 } } = 8.3 \pm 3.0 \times 10 ^ { 10 } M _ { \odot } , which given the dynamical mass of the system is consistent with a CO–H _ { 2 } conversion factor of \alpha = 5.5 \pm 2.0 M _ { \odot } ( K km s ^ { -1 } pc ^ { 2 } ) ^ { -1 } .
This suggests that the star-formation efficiency is dependent on the host galaxy morphology as opposed to the nature of the AGN .
The far-infrared continuum spectral energy distribution shows evidence for heated dust , equivalent to an obscured star-formation rate of { SFR } = 69 ^ { +41 } _ { -25 } \times ( 7.3 / \mu _ { IR } ) M _ { \odot } yr ^ { -1 } , which demonstrates the composite star-forming and AGN nature of this system .