The Ly<i>α</i> and Continuum Origins Survey. I. Survey Description and Ly<i>α</i> 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 in identifying the global galaxy properties linked to the ionizing escape fraction <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">esc</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">LyC</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> , little is currently known about how spatially resolved galaxy properties impact it. We present Hubble Space Telescope (HST) imaging data obtained in the Ly α and Continuum Origins Survey (LaCOS). LaCOS consists of HST imaging covering rest-frame optical and UV bands for a subsample of 42 galaxies in the Low redshift Lyman Continuum Survey, including 22 LyC emitters ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>f</mml:mi> <mml:mi>esc</mml:mi> <mml:mi>LyC</mml:mi> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mn>0.01</mml:mn> <mml:mo>-</mml:mo> <mml:mn>0.49</mml:mn> </mml:math> ). Here, we describe the sample, observations, and data reduction, and investigate connections between global and sub-kiloparsec Ly α emission and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">esc</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">LyC</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> . We confirm the correlation between <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">esc</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">LyC</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> and EW Ly α , 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 α , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">esc</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">Ly</mml:mi> <mml:mi>α</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> , Σ SFR , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">esc</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">LyC</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> , but with a smaller degree of correlations ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mo stretchy="false">∣</mml:mo> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:mi>τ</mml:mi> <mml:mo stretchy="false">∣</mml:mo> </mml:mrow> <mml:mrow> <mml:mo stretchy="true">¯</mml:mo> </mml:mrow> </mml:mover> <mml:mo>∼</mml:mo> <mml:mn>0.1</mml:mn> </mml:math> ). We find correlations are strongest between Ly α observables ( L Ly α , EW Ly α ) and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">esc</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">LyC</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> 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.