As late as 1995, the anticipated widespread population of primeval galaxies remained at large, lurking undetected at unknown redshifts, with undiscovered properties. We present results from our efforts to detect and characterize primeval galaxies by their signature high-redshift Lyman-alpha emission lines utilizing two observational techniques: serendipitous slit spectroscopy and narrowband imaging. By pushing these techniques to their utmost limits, we probe the Lyman-alpha-emitting galaxy population out to redshifts as high as z = 6.5. Galaxies at this epoch reside in a universe which is just 800 million years old, a mere 6% of its current age. As such, this work provides one account of the manner by which observational cosmology has recently shifted from merely marveling at the incredible lookback times implied by the first few high-redshift detections, to the routine assembly of high-redshift datasets designed to address specific astrophysical issues.

This thesis presents studies on Ly[alpha] emitting galaxies (LAEs) at high redshift. The main goal of this work is to understand the nature and evolution of LAEs, with the broader aim of gaining insights into galaxy formation and evolution in general. We achieve the stated goal by constraining the stellar populations of LAEs at z ~ 3 - 6 using detailed multiwavelength observations. Using deep Spitzer IRAC imaging, we study the stellar populations of LAEs at z = 5.7 and 6.6. IRAC observations sample the rest-frame optical emission from the z ~ 6 LAEs, thus allowing the stellar masses and star formation histories of the galaxies to be constrained. Interestingly, we find that IRAC-detected LAEs at z ~ 6 can be massive and evolved, unlike typical LAEs at lower redshifts. Extending our work to lower redshift, we study the overall properties of LAEs at z = 3.1 using a large sample of 162 objects. The majority of the LAEs in our sample are young and low-mass galaxies but there is also a significant fraction of older and more massive objects. The fact that Ly[alpha] emission can be seen in both young and evolved galaxies has interesting implications for the evolution of LAEs. In a further study, we use a combined sample of 40 spectroscopically selected and 111 photometrically selected objects to constrain the average stellar population of LAEs at z = 5.7. Surprisingly, the z = 5.7 LAEs in our sample appear to be more massive on average than their low-redshift counterparts. Additionally, we demonstrate that at higher redshift LAEs account for a larger fraction of the global stellar mass density and star formation rate density. Our results suggest a possible evolution of LAEs towards higher mass with redshift, potentially due to the increasing prevalence of Ly[alpha] emission as a result of the lower overall dust content in high-redshift galaxies.

We present 36 spectroscopically confirmed Lyman-alpha emitting galaxies (LAEs) from follow-up observations with Keck/DEIMOS of high-redshift candidates behind 10 galaxy cluster lenses. High-redshift candidates were selected to be between 5 [less than or approximately equal to] z [less than or approximately equal to 7] from a variety of photometric data using HST and Spitzer imaging surveys including the Cluster Lensing And Supernova Survey with Hubble (CLASH), the Hubble Frontier Fields (HFF), and the Spitzer UltRa Faint SUrvey Program (SURFSUP). A subset of 27 of our targets were prioritized from the Grism Lens-Amplified Survey from Space (GLASS). After compiling a large sample of potential high-redshift candidates from our extensive spectroscopic program, we used photometric redshift information derived from accompanying photometric data to perform an integrated P(z) cut >1% between 5 z 7 in order to construct a sample of 198 high-redshift objects, 136 primary targets and 62 secondaries (serendipitous objects). Our high-redshift sample spans intrinsic UV luminosities from a few L* down to 0.001L* (where L* is the characteristic luminosity of galaxies in our redshift range). We identified 19 high-confidence detections of Ly[alpha] in our final sample and an additional 17 likely detections. Five of these detections have been previously reported spectroscopically. We divided our sample into a lower-redshift (z [approximately equal to] 5.5) and higher-redshift (z [approximately equal to] 6.5) sample and ran Monte Carlo trials, incorporating the strength of the Ly[alpha]emission, the photometric redshift of the non-detections, and different treatments of multiple images. Considering only objects where Ly[alpha]could be detected at EW(Ly[alpha])25Å at 3[sigma] at the fiducial depth of our survey, and considering only those galaxies with EW(Ly[alpha])25Å as true LAEs, and finally, considering only objects with m[subscript AB]

And with model predictions, indicates that bright Ly-alpha galaxies are so rare beyond z=5 that a non-evolving population can be excluded.

The reference work on astrophysics to provide a comprehensive introduction to the physics of Interstellar Matter. The objective of the book is to show how physics can be applied to the understanding and diagnosis of the phase structure, the physical conditions and the chemical make-up and evolution of the interstellar medium. Unlike other textbooks in the field, here a more systematic approach has been adopted based on the authors' lecture course experience. It is aimed primarily at those undertaking post-graduate courses, or those doing advanced projects as part of honours undergraduate courses in physics or astrophysics.

The hydrogen Lyman-alpha line is of utmost importance to many fields of astrophysics. This UV line being conveniently redshifted with distance to the visible and even near infrared wavelength ranges, it is observable from the ground, and provides the main observational window on the formation and evolution of high redshift galaxies. Absorbing systems that would otherwise go unnoticed are revealed through the Lyman-alpha forest, Lyman-limit, and damped Lyman-alpha systems, tracing the distribution of baryonic matter on large scales, and its chemical enrichment. We are living an exciting epoch with the advent of new instruments and facilities, on board of satellites and on the ground. Wide field and very sensitive integral field spectrographs are becoming available on the ground, such as MUSE at the ESO VLT. The giant E-ELT and TMT telescopes will foster a quantum leap in sensitivity and both spatial and spectroscopic resolution, to the point of being able, perhaps, to measure directly the acceleration of the Hubble flow. In space, the JWST will open new possibilities to study the Lyman-alpha emission of primordial galaxies in the near infrared. As long as the Hubble Space Telescope will remain available, the UV-restframe properties of nearby galaxies will be accessible to our knowledge. Therefore, this Saas-Fee course appears very timely and should meet the interest of many young researchers.