and ALMA.

$\chi^{2}$ values are also reduced for an obscured AGN template at $z=0.6$ which has the observed 16[$\mu$m]{} flux density suppressed relative to the flux density at 22[$\mu$m]{} and 24[$\mu$m]{} due to the entrance of the 9.7[$\mu$m]{}silicate absorption feature. An obscured AGN template like Mrk231 can also fit the 8[$\mu$m]{} flux density of the source as shown in Figure 4 while the starburst template fits at $z\sim1.7$ require the optical/near-infrared flux to be dominated by starlight (Figure 6). The non-detection of any spectral lines in the optical/near-infrared spectroscopic data presented by @Mobasher, as well as the difficulty in accounting for the non-detection of the source at optical wavelengths (Section 3.3) makes the $z\sim0.6$ hypothesis unlikely. On the other hand, $z\sim1.7$ lies within the so-called redshift “desert", where the \[OII\] $\lambda$3727 doublet, \[OIII\] $\lambda$5007 line and H$\alpha$+\[NII\] lines are all severely affected by atmospheric transmission and strong OH sky lines. Furthermore, as we discuss in Section 3.3, at $z=1.7$, the red SED of the source between 2.2$\mu$m and IRAC 3$-$8[$\mu$m]{} could be due to the broad 1.6[$\mu$m]{} bump in the stellar SED being in the IRAC passbands.

We now consider the implications of the IRS detections to the high redshift 