  We have obtained deep J & Ks-band images centered on a bright radio quiet QSO
UM402 (z_{em}=2.856) using IRCS camera and AO systems on Subaru Telescope, as
well as retrieved WFC3/F140W archive images. A faint galaxy (m_{k}=23.32 +/-
0.05 in the Vega system) that lies ~ 2.4" north of the QSO sightline has been
clearly resolved in all three deep high resolution datasets, and appears as an
irregular galaxy with two close components in the Ks-band images (separation ~
0.3"). Given the small impact parameter (b=19.6 kpc, at z_{lls}=2.531), as well
as the red color of (J-Ks)_{vega} ~ 1.6, it might be a candidate galaxy giving
rise to the Lyman Limit system absorption at z_{abs}=2.531 seen in the QSO
spectrum. After carefully subtracting the PSF from the QSO images, the host
galaxy of this bright radio quiet QSO at z ~ 3 was marginally revealled. We
placed a low limit of the host component of m_{k} ~ 23.3 according to our
analyses.
