Harnessing the Power of Gravitational Lensing: Resolved Star Formation at Redshift 1 - 4

Abstract

In the coming decade, new observational facilities will enable galaxies seen in the first half of the Universe's history (z > 1) to be mapped on ~100pc scales routinely for the first time. As a preview of the science capabilities of these facilities, we can use clusters of galaxies, the largest gravitationally-bound structures in the Universe, as natural telescopes. Using this technique, we examine star formation within galaxies at 1 < z < 5, during the peak epoch of cosmic star formation density.

We begin in Chapter 3 by targeting Halpha emission with narrowband imaging from HST/WFC3 in eight lensed galaxies at z = 1 - 1.5. We identify star-forming clumps in these galaxies and compare their properties directly to those of local spirals.

In Chapter 4 we consider the fuel for star formation, with a search for molecular gas in a z ~ 5 lensed galaxy. We obtain a tentative detection that implies a gas fraction Mgas/(Mgas + M*) ~0.6, suggesting slow evolution at z > 2.

In Chapter 5, we present the largest survey to date of gravitationally-lensed galaxies observed with integral field spectroscopy. We present observations of 12 new galaxies, increasing the total sample to 17 lensed galaxies at 1 < z < 4 observed on 100pc scales, and investigate the global disc dynamics and map the star formation.

With these combined observations, we present a simple theoretical model in which star formation in galaxy discs is driven by the same physical processes at all redshifts. We find that the scale of collapse depends on the galaxy's gas content and kinematics, and show that our observations are consistent with the necessary evolution in these properties.