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High Lyman Continuum Escape Fraction in a Lensed Young Compact Dwarf Galaxy at $z=2.5$

, , , , and .
(2017)cite arxiv:1702.06540Comment: 5 pages, 2 figures, accepted by ApJL.

Abstract

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 $łog(M/M_ødot=9.14$ and SFR is 12.5~$M_ødot$~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.

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