The high-redshift Universe as seen through galaxy cluster gravitational lenses

Abstract

Measurements of high redshift sources can help address important open questions in astrophysics and help us better understand how galaxies and star formation processes evolve over cosmic time. Gravitational lensing allows us to observe and study these intrinsically faint galaxies at high redshifts that may otherwise be undetectable with modern telescopes. Galaxy cluster-scale gravitational lenses can magnify the flux from background galaxies by up to a factor of ~50 and stretch their spatial extent so that compact features can be resolved, allowing us to study their physical properties in more detail than would be possible without the aid of lensing. This thesis presents observational analyses of three high redshift sources that are strongly lensed by galaxy clusters. The first source is a multiply-imaged spiral galaxy at redshift z = 1.49. Due to lensing by the MACS J1149 galaxy cluster, this highly magnified background galaxy displays over a dozen individually resolved HII regions. Using integral field unit spectroscopy to measure the Balmer emission line fluxes and widths, we find that the HII regions in this galaxy at z = 1.49 have significantly higher Balmer luminosities than predicted by the empirical relationship between velocity dispersion and Balmer luminosity that exists for HII regions in the local Universe. The second source discussed in this thesis is an extremely compact galaxy with bright nebular emission lines at z = 9.51. The galaxy is highly magnified by the RX J2129 galaxy cluster, allowing for a measurement of its physical half-light radius, R = 16.2+4.6-7.2 parsec. Despite its tiny size, the Hβ flux suggests that galaxy is highly star-forming, with a star formation surface density ΣSFR>1000 solar masses per year per square kiloparsec. The final source presented in this thesis is a caustic-crossing lensed galaxy at z = 0.94, in which nine individual massive stars were detected and resolved in microlensing transient events. We model the temperatures and magnitudes of these stars and find that they are all likely red supergiants with temperature of approximately 4,000 K. One of these transient events is likely a caustic-crossing binary system consisting of a red supergiant and a hot companion star.