  The intra-cluster light (ICL) in observations is usually identified through
the surface brightness limit method. In this paper, for the first time we
produce the mock images of galaxy groups and clusters using a cosmological
hydro- dynamical simulation, to investigate the ICL fraction and focus on its
dependence on observational parameters, e.g., the surface brightness limit
(SBL), the effects of cosmological redshift dimming, point spread function and
CCD pixel size. Detailed analyses suggest that the width of point spread
function has a significant effect on the measured ICL fraction, while the
relatively small pixel size shows almost no influence. It is found that the
measured ICL fraction depends strongly on the SBL. At a fixed SBL and redshift,
the measured ICL fraction decreases with increasing halo mass, while with a
much faint SBL, it does not depend on halo mass at low redshifts. In our work,
the measured ICL fraction shows clear dependence on the cosmological redshift
dimming effect. It is found that there are more mass locked in ICL component
than light, suggesting that the use of a constant mass-to-light ratio at high
surface brightness levels will lead to an underestimate of ICL mass.
Furthermore, it is found that the radial profile of ICL shows a characteristic
radius which is almost independent of halo mass. The current measurement of ICL
from observations has a large dispersion due to different methods, and we
emphasize the importance of using the same definition when observational
results are compared with the theoretical predictions.
