$f_{\rm gas} = 0.32$, and the galaxy forms stars at a rate of $366\ M_{\sun}/yr$.

SDP.11 is reconstructed, in the near-IR, in a complex combination of several knots distributed within a region of a few kpc, which are responsible for the small-scale structure observed in the $\sim0.84$ arcsec radius Einstein ring (Dye et al. 2014). According to the SED fitting, compared to SDP.9, the source has a higher star formation rate, SFR$=650\ M_{\sun}/yr$, and a higher mass in stars $M\star \sim 1.9 \times 10^{11} M_{\sun}$. Lupu et al. (2012) CO observations indicate a comparable gas mass $M_{\rm gas} \sim 3.0 \times 10^{10} M_{\sun}$ and hence a lower gas fraction, $f_{\rm gas} = 0.14$.

We note that Lupu et al. (2012) adopted a linear relation ($M_{gas}=\alpha_{CO}L_{CO}$) to convert CO luminosity to gas mass with slope $\alpha_{CO}=0.8$, comparable with typical values observed in local ULIRGs. Recent observations in the radio and mm bands of starburst galaxies at $z> 1.5$ (Aravena et al. 2016, Bethermin et al. 2016, Popping et al. 2017) indicate that $0.8<\alpha_{CO}<1.5$ for populations of galaxies similar to our targets. This indicates that our mass estimates are most likely a lower limit of the actual gas mass content of the 