School of Physics - Theses
Permanent URI for this collection
Search Results
1 - 1 of 1
-
ItemGravitational lensing and clustering of galaxies in the epoch of reionization( 2015)The epoch of reionization marks the period where neutral hydrogen in the intergalactic medium was ionized by high energy photons emitted by the first stars and galaxies. Observations of galaxies during this period aim to uncover the types of stars and galaxies that were responsible for producing the ionizing flux to complete reionization within one billion years after the Big Bang (by z~6), and study the formation of the first galaxies in the Universe. These galaxies are observed in the near-infrared (NIR) today, and so require space-based observatories with sensitive NIR cameras such as Wide Field Camera 3 on the Hubble Space Telescope (HST). Considerable effort has been dedicated to ultradeep observations with HST in order to identify galaxies in the epoch of reionization. Surveys such as the eXtreme Deep Field (XDF), Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), Early Release Science (ERS) and the Brightest of Reionizing Galaxies (BoRG) have now discovered hundreds of these galaxies. This thesis makes use of these observations to address two important topics: how gravitational lensing affects the observations of such galaxies, and what their spatial distribution can tell us about the underlying dark matter distribution at this early time. Photons emitted by the first galaxies traverse most of the Universe’s history before reaching our telescopes. As such, they are subject to gravitational lensing by foreground galaxies along the line of sight. Gravitational lensing can result in the magnification of high redshift galaxies, skewing their observed luminosities. Because bright galaxies are significantly rarer than their fainter counterparts, the chance of gravitational magnification for observationally bright galaxies is significantly enhanced. This effect is known as magnification bias. We use the largest samples of Lyman-break galaxy (LBG) candidates observed in the first 1:5 billion years after the Big Bang (46.5. The clustering signal at z~7 is detected at >4 sigma, and corresponds to a real-space correlation length of r_0 = 6.7 +0.9/-1.0 cMpc, a galaxy bias of b = 8.6 +/- 0:9, and dark matter haloes of mass M = 10^(11:3+0:2/-0.3) M_sun . We reassess the clustering of LBGs at z=4–6 and find a trend of increasing bias from z=3.8 (b~3.0) to z=7:2 (b~8.6). We use these measurements to infer the fraction of dark matter haloes hosting UV-bright galaxies, and find that values near unity are preferred at z=7.2, which may be explained by the shorter halo assembly time at high redshift.