from Source Extractor is slightly larger than the background noise (2.6 nJy), thus conservatively took the larger one. The stamp image and 1$\sigma$ upper limit for the flux of the stack are shown in Figure \[fig:sed\]. The stacking yielded no identifiable emission at the position of the source. The measured stack flux is $6 \sigma$ lower than the prediction from the low-$z$ solution, further indicating the preference for the high-$z$ interpretation of the source.

We conclude that the detected line is Ly$\alpha$. z7\_GSD\_3811 is a galaxy bright in the UV with the rest-frame UV absolute magnitude of $M_{\rm UV} \sim -21.2$, about two times brighter in luminosity than the characteristic UV magnitude of the rest-frame UV luminosity function at $z=8$ of $M_{{\rm UV}, z=8}^*=-20.48$ [@finkelstein15a]. Other physical properties inferred from our SED fitting analysis indicate that z7\_GSD\_3811 is a typical galaxy at $z=$ 7–8 [*for its UV magnitude*]{}, with a moderately blue UV slope ($\beta= -2.2^{+0.3}_{-0.2}$), dust-corrected UV-based star formation rate (SFR) of $33^{+56}_{-9}$ [$M_{\odot}$]{} yr$^{-1}$, and stellar mass of $\log(M_*$/[$M_{\odot}$]{})$=9.3^{+0.5}_{-0.4}$. This galaxy was noted as a promising $z\gtrsim7$ candidate by several other previous [*HST*]{} imaging studies as well [@bouwens10; @mclure13]. Table \[tab:3811\] summarizes the physical properties of z7\_GSD\_3811.

L$\alpha$ 