The Lyman-alpha and Continuum Origins Survey. I. Survey description and Ly$\alpha$ imaging

Abstract

Understanding the mechanisms driving the escape of ionizing or Lyman continuum (LyC) emission from the interstellar medium of galaxies is necessary to constrain the evolution of reionization, and the sources responsible for it. While progress has been made into identifying the global galaxy properties linked to the escape fraction of ionizing radiation, $f_{esc}^{LyC}$, little is currently known about how spatially resolved galaxy properties impact this parameter. We present Hubble Space Telescope (HST) imaging data obtained as part of the Lyman $\alpha$ and Continuum Origins Survey (LaCOS). LaCOS consists of HST imaging in 5 filters covering rest-frame optical and UV bands for a subsample of 42 galaxies in the Low redshift Lyman Continuum Survey, 22 being Lyman continuum emitters ($f_{esc}^{LyC}=0.01-0.49$). Here, we describe the sample, observations and data reduction, and investigate connections between global and sub-kpc Lyman $\alpha$ (Ly$\alpha$) emission, and $f_{esc}^{LyC}$. We confirm the correlation between $f_{esc}^{LyC}$ and EW${}_{Ly\alpha }$ , and the anticorrelation with $r_{50}$, when using values obtained via global photometry. We also find correlations previously found with spectroscopy with global photometric $L_{Ly\alpha }$, $f_{esc}^{Ly\alpha }$, ${\Sigma }_{SFR}$ , and $f_{esc}^{LyC}$, but with a smaller degree of correlation ($\overline{|\Delta \tau |}\sim 0.1$). We find correlations are strongest between $Ly\alpha$ observables ($L_{\mathrm{Ly}\alpha }$, EW${}_{\mathrm{Ly}\alpha }$) and $f_{\mathrm{esc}}^{\mathrm{LyC}}$ when measured in a small aperture around the brightest UV source in each galaxy. We interpret these results as evidence that LyC photons escaping on the line-of-sight are contributed by a small number of UV-bright compact regions in most galaxies in LaCOS.

Accepted for publication in ApJS

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