Abstract
Galaxy evolution studies have been revolutionized by the advent of near-infrared observations over the last decade. An intriguingly population of distant red galaxies, only visible at near-infrared wavelengths, was discovered. They were previously overlooked, since they are invisible even in the deepest Hubble Space Telescope (HST) optical surveys. Their stellar populations, characterized using deep near-infrared photometric and spectroscopic observations, reveal that they are the most massive and evolved galaxies at early epochs. This suggests that they have undergone a rapid build-up of stellar mass followed by a short-lived, effective phase of star formation quenching. Curiously, their stellar densities are an order of magnitude higher than their local counterparts, containing 1011 solar masses within a radius of only 1.5 kpc. No similar galaxies exist in the local Universe, therefore they must undergo significant size evolution to become present-day giant ellipticals. The need for further evolution lends strong support to the idea that large galaxies form from hierarchal assembly, effective ruling out the monolithic collapse model. It is therefore important to understand the formation and evolution of this peculiar population of compact, massive quiescent galaxies, which in turn provides constraints to galaxy formation models.
Despite the wealth of observations, the dominant physical mechanisms driving the evolution of galaxies are still fiercely debated. Is galaxy merging a dominant mechanism in evolving the sizes and stellar masses of quiescent galaxies? Are quiescent galaxies truly passive, or are their stellar populations in fact not old but reddened by dust? The goal of this thesis is to address these two outstanding questions, in order to verify the existence of such an extreme galaxy population, and to measure the contribution of galaxy merging in evolving them into local ellipticals. In Chapter 1, I provide a broad overview of the current understanding of this population of quiescent massive galaxies, from their initial discovery a decade ago, to the latest findings based on state-of-the-art observations as well as theoretical models.
Despite the wealth of observations, the dominant physical mechanisms driving the evolution of galaxies are still fiercely debated. Is galaxy merging a dominant mechanism in evolving the sizes and stellar masses of quiescent galaxies? Are quiescent galaxies truly passive, or are their stellar populations in fact not old but reddened by dust? The goal of this thesis is to address these two outstanding questions, in order to verify the existence of such an extreme galaxy population, and to measure the contribution of galaxy merging in evolving them into local ellipticals. In Chapter 1, I provide a broad overview of the current understanding of this population of quiescent massive galaxies, from their initial discovery a decade ago, to the latest findings based on state-of-the-art observations as well as theoretical models.
| Original language | English |
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| Publisher | The Niels Bohr Institute, Faculty of Science, University of Copenhagen |
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| Publication status | Published - 2014 |