Gas and dust in early galaxy evolution

Abstract: In order to study the content of distant galaxies without focusing solely on the brightest objects -- the tip of the iceberg -- I developed a tool:  LineStacker. As its name indicates this tool was designed to perform spectral stacking analyses. Stacking allows to shed light on otherwise invisible features, by averaging together observations of many sources from a common galaxy population. Spectral lines emitted or absorbed by galaxies and the intergalactic medium carry information on the content of galaxies as well as their dynamics. The luminosity of certain atomic and molecular spectral lines is known to correlate with fundamental physical properties of galaxies, such as star formation rate. In addition, the shape of the lines can trace global dynamics of galaxies or peculiar events such as outflows. In this context, I used LineStacker to study distant galaxies by observing the average spectral lines, or continuum emission, emitted by a particular galaxy population. In this thesis I present the tool LineStacker in detail and with a specific emphasis on the statistical tools included with it. In addition, I showcase three different analyses where we used LineStacker to study galaxy evolution. In the two first we studied ionized carbon, [CII], in galaxies at redshift z∼6. One project focused on the faint outflow signatures below the main [CII] line, while the other project focused on the overall [CII] emission from faint, gravitationally lensed galaxies. Finally, in the last analysis, we studied the overall dust mass as well as the comoving dust mass density and their evolution with redshift. The results from all the analyses highlight the power and efficiency of stacking as a method, and the necessity to go beyond studying the brightest objects.