High Lyman Continuum Escape Fraction in a Lensed Young Compact Dwarf
  Galaxy at $z=2.5$
  We present the HST WFC3/F275W UV imaging observations of A2218-Flanking, a
lensed compact dwarf galaxy at redshift $z\approx2.5$. The stellar mass of
A2218-Flanking is $\log(M/M_{\odot}=9.14$ and SFR is 12.5$M_\odot$yr$^{-1}$
after correcting the magnification. This galaxy has a young galaxy age of 127
Myr and a compact galaxy size of $r_{1/2}=2.4$kpc. The HST UV imaging
observations cover the rest-frame Lyman continuum (LyC) emission
($\sim800${\AA}) from A2218-Flanking. We firmly detect ($14\sigma$) the LyC
emission in A2218-Flanking in the F275W image. Together with the HST F606W
images, we find that the absolute escape fraction of LyC is $f_{\rm
abs,esc}>28-57\%$ based on the flux density ratio between 1700{\AA} and
800{\AA} ($f_{1700}/f_{800}$). The morphology of the LyC emission in the F275W
images is extended and well follows the morphology of the UV continuum
morphology in the F606W images, suggesting that the $f_{800}$ is not from
foreground contaminants. We find that the region with a high star formation
rate surface density has a lower $f_{1700}/f_{800}$ (higher $f_{800}/f_{1700}$)
ratio than the diffused regions, suggesting that LyC photons are more likely to
escape from the region with the intensive star-forming process. We compare the
properties of galaxies with and without LyC detections and find that LyC
photons are easier to escape in low mass galaxies.
