Lyman Continuum and Lyman alpha Emission from Galaxies at High Redshift

In this thesis we present two studies of star-forming galaxies at z ≈2--3 based on deep spectroscopic and narrow band imaging observations. The first study addresses pressing questions regarding the nature of galaxies with significant escaping Lyman continuum radiation. Our second study investigates the nature of spatially extended Lyman alpha emission first observed in the form of luminous Lyman alpha "blobs.".;In part I of this thesis we present the results of a deep spectroscopic survey to detect Lyman continuum radiation from individual galaxies at z ≈ 3. Our measurements suggest that the escape fraction is strongly variable among galaxies at all luminosities, but that there is a significant preference for higher escape fraction in objects with luminosity lower than L*. The integrated escaping radiation from galaxies is sufficient to complement the contribution of AGN in keeping the hydrogen in the Universe ionized. Using supporting near-IR and mid-IR photometry we derive model stellar population parameters and discover that Lyman continuum is preferentially detected among objects with lowest values for dust extinction and star-formation rate. This finding may indicate a connection between Lyman continuum escape and the evolutionary stage of a galaxy.;In part II we present deep imaging observations in a narrow band centered on Lyman&agr; and H&agr; at the redshift of a known protocluster of star-forming galaxies (z = 2.3). We discover 6 new giant and bright Lyman&agr; "blobs" and identify a large number of Lyman&agr; and H&agr; emitters at the protocluster redshift. We find an anticorrelation between Lyman&agr; and H&agr; selection, which is explained by the observation that H&agr; emitters show Lyman&agr; line in absorption in their spectra. However, the composite Lyman&agr; narrow-band image of H&agr; emitters uncovers extended emission resembling Lyman&agr; blobs in miniature. We conclude that faint Lyman&agr; emission from gas within a radius of 40 kpc (or more) is likely a feature common to most galaxies at these redshifts. If ionizing photons produced in star-forming regions are responsible for this faint Lyman&agr; "glow", then this extended flux represents a significant fraction of total predicted Lyman&agr; equivalent width.