The Space Density, Environments, and Physical Properties of Large Ly α Nebulae

Abstract

Powerful forces are at work in giant Ly α nebulae, a rare and mysterious population in the high redshift universe. Much like the spatially extended emission line halos around high redshift radio galaxies . but without the strong radio emission . Ly α nebulae (or Ly α 'blobs') boast copious Ly α emission (10⁴⁴ erg s⁻¹), large sizes (∼100 kpc), complex gas morphologies, and the company of numerous compact, star-forming galaxies, and may offer a window into dramatic episodes of massive galaxy formation. The small sample sizes and complex inner workings of Ly α nebulae have limited progress on understanding the their space density, environments, and physical conditions. This thesis strives to answer fundamental questions about Ly α nebulae and pave the way for understanding their role in the build up of massive galaxy systems. To address the frequency of collapse of these massive structures, we carried out the largest systematic Ly α nebula survey to date and measured the Ly α nebula space density. As an unbiased test of the environment of Ly α nebulae, we studied the surroundings of a Ly α nebula and confirmed that Ly α nebulae reside preferentially in overdense regions. To disentangle the sources of ionization, we took a census of all the compact ionization sources within a large Ly α nebula using high resolution imaging. Finally, we used photoionization modeling to put constraints on the physical conditions, the metallicity, and the sources of ionization within Ly α nebulae. Future work will be able to build on this thesis by expanding the systematic search for Ly α nebulae to other existing deep broad-band datasets, mapping the three-dimensional overdense structures in which Ly α nebulae live out to ≥ 50 (comoving) Mpc scales, and disentangling multiple sources of ionization within a larger sample of individual systems using deep optical and near-infrared spectroscopy and detailed photoionization modeling.