Searching for candidates of Lyman continuum sources - revisiting the
  SSA22 field
  We present the largest to date sample of hydrogen Lyman continuum (LyC)
emitting galaxy candidates at any redshift, with 18 Ly$\alpha$ Emitters (LAEs)
and 7 Lyman Break Galaxies (LBGs), obtained from the SSA22 field with
Subaru/Suprime-Cam. The sample is based on the 159 LAEs and 136 LBGs observed
in the field, all with spectroscopically confirmed redshifts, and these LyC
candidates are selected as galaxies with counterpart in a narrow-band filter
image which traces LyC at $z\geq 3.06$. Many LyC candidates show a spatial
offset between the rest-frame non-ionizing ultraviolet (UV) detection and the
LyC-emitting substructure or between the Ly$\alpha$ emission and LyC. The
possibility of foreground contamination complicates the analysis of the nature
of LyC emitters, although statistically it is highly unlikely that all
candidates in our sample are contaminated by foreground sources. Many viable
LyC LAE candidates have flux density ratios inconsistent with standard models,
while also having too blue UV slopes to be foreground contaminants. Stacking
reveals no significant LyC detection, suggesting that there is a dearth of
objects with marginal LyC signal strength, perhaps due to a bimodality in the
LyC emission. The foreground contamination-corrected $3\sigma$ upper limits of
the observed average flux density ratios are $f_{LyC}/f_{UV}<0.08$ from
stacking LAEs and $f_{LyC}/f_{UV}<0.02$ from stacking LBGs. There is a sign of
a positive correlation between LyC and Ly$\alpha$, suggesting that both types
of photons escape via a similar mechanism. The LyC detection rate among
proto-cluster LBGs is seemingly lower compared to the field.
