Topics in Galaxy Evolution: Early Star Formation and Quenching

Citation

Gonçalves, Thiago Signorini (2012) Topics in Galaxy Evolution: Early Star Formation and Quenching. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/E5T6-AC13. https://resolver.caltech.edu/CaltechTHESIS:06052012-140445171

Abstract

In this thesis, we present three projects designed to shed light on yet unanswered questions on galaxy formation and evolution. The first two concern a sample of UV-bright starburst galaxies in the local universe (z~0.2). These objects are remarkably similar to star-forming galaxies that were abundant at high redshifts (2<z<3) - the Lyman break galaxies - and can help explain the very distinctive properties observed at such epochs. Thus, these galaxies are denominated Lyman break analogs, or LBAs.

First, we describe a survey of kinematics of the nebular gas in such objects, and how that can help explain the formation process, including gas assembly, in these starbursts. We show strong evidence that the gas kinematics resemble those observed at high redshifts. However, by artificially manipulating our observations to mimic our objects at greater distances, we show how low resolution and signal-to-noise ratios can lead to erroneous conclusions, in particular when attempting to diagnose mergers as the origin of the starburst.

Then, we present results from a pilot survey to study the cold, molecular gas reservoir in such objects. Again, we show that the observed properties are analogous to those observed at high redshift, in particular with respect to baryonic gas fractions in the galaxy, higher than normally found in low-extinction objects in the local universe. Furthermore, we show how gas surface density and star-formation surface density follow the same relation as local galaxies, albeit at much higher values.

Finally, we discuss an observational project designed to measure the mass flux density from the blue sequence to the red sequence across the so-called green valley. We obtain the deepest spectra ever observed of green valley galaxies at intermediate redshifts (z~0.8) in order to measure spectral features from which we can measure the star formation histories of individual galaxies. We measure a mass flux ratio that is higher than observed in the local universe, indicating the red sequence was growing faster when the universe was half its present age than today.

Thesis Files