We present ALMA observations of the [ \ion C2 ] fine structure line and the underlying far–infrared ( FIR ) dust continuum emission in J1120+0641 , the most distant quasar currently known ( z = 7.1 ) .
We also present observations targeting the CO ( 2-1 ) , CO ( 7-6 ) and [ \ion C1 ] 369 \mu m lines in the same source obtained at the VLA and PdBI .
We find a [ \ion C2 ] line flux of F _ { \mathrm { [ CII ] } } = 1.11 \pm 0.10 Jy km s ^ { -1 } and a continuum flux density of S _ { \mathrm { 227 GHz } } = 0.53 \pm 0.04 mJy beam ^ { -1 } , consistent with previous unresolved measurements .
No other source is detected in continuum or [ \ion C2 ] emission in the field covered by ALMA ( \sim 25 \arcsec ) .
At the resolution of our ALMA observations ( 0 \farcs 23 , or 1.2 kpc , a factor \sim 70 smaller beam area compared to previous measurements ) , we find that the majority of the emission is very compact : a high fraction ( \sim 80 % ) of the total line and continuum flux is associated with a region 1–1.5 kpc in diameter .
The remaining \sim 20 % of the emission is distributed over a larger area with radius \lesssim 4 kpc .
The [ \ion C2 ] emission does not exhibit ordered motion on kpc-scales : applying the virial theorem yields an upper limit on the dynamical mass of the host galaxy of ( 4.3 \pm 0.9 ) \times 10 ^ { 10 } M _ { \sun } , only \sim 20 \times higher than the central black hole .
The other targeted lines ( CO ( 2-1 ) , CO ( 7-6 ) and [ \ion C1 ] ) are not detected , but the limits of the line ratios with respect to the [ \ion C2 ] emission imply that the heating in the quasar host is dominated by star formation , and not by the accreting black hole .
The star-formation rate implied by the FIR continuum is 105–340 M _ { \sun } yr ^ { -1 } , with a resulting star-formation rate surface density of \sim 100–350 M _ { \sun } yr ^ { -1 } kpc ^ { -2 } , well below the value for Eddington–accretion–limited star formation .