The gravitationally-lensed galaxy A1689-zD1 is one of the most distant spectroscopically confirmed sources ( z = 7.5 ) .
It is the earliest known galaxy where the interstellar medium ( ISM ) has been detected ; dust emission was detected with the Atacama Large Millimetre Array ( ALMA ) .
A1689-zD1 is also unusual among high-redshift dust emitters as it is a sub-L* galaxy and is therefore a good prospect for the detection of gaseous ISM in a more typical galaxy at this redshift .
We observed A1689-zD1 with ALMA in bands 6 and 7 and with the Green Bank Telescope ( GBT ) in band Q .
To study the structure of A1689-zD1 , we map the mm thermal dust emission and find two spatial components with sizes about 0.4 - 1.7 kpc ( lensing-corrected ) .
The rough spatial morphology is similar to what is observed in the near-infrared with HST and points to a perturbed dynamical state , perhaps indicative of a major merger or a disc in early formation .
The ALMA photometry is used to constrain the far-infrared spectral energy distribution , yielding a dust temperature ( T _ { dust } \sim 35 – 45 K for \beta = 1.5 - 2 ) .
We do not detect the CO ( 3-2 ) line in the GBT data with a 95 % upper limit of 0.3 mJy observed .
We find a slight excess emission in ALMA band 6 at 220.9 GHz .
If this excess is real , it is likely due to emission from the [ C ii ] 158.8 \mu m line at z _ { [ CII ] } = 7.603 .
The stringent upper limits on the [ C ii ] L _ { FIR } luminosity ratio suggest a [ C ii ] deficit similar to several bright quasars and massive starbursts .