Program: GN-2015B-Q-14

We propose to perform Y- and J-band imaging of a faint QSO candidates (J ~ 22.5 AB mag) at z ~ 7, selected from the Infrared Medium-deep Survey imaging data. It has been chosen through a rigorous multi-color selection criteria. No QSOs as faint as these have been found at z=7, and this QSO could be the highest redshift QSO identified thus far. While it is a promising candidate, the ambiguity remains as to this object being a lower redshift interloper. The proposed observation will add critical data points in the broad-band spectral energy distribution (SED) to determine its high redshift nature. This step is a must for us to comfortably move forward for very deep spectroscopy to determine its redshfits. The imaging observation itself can also be helpful to put constraints on the number density of faint z=7 QSOs which has never been determined before. Since the observing time is modest, the observation of the targets is ideal as filler or backup observation.