Massive Galaxies in the Early Universe: A Detailed Spectroscopic and Structural Investigation
Marsan, Zehra Cemile.
Abstract: The existence of numerous very massive galaxies in the early
universe revealed by deep imaging surveys has been at odds with predictions from models of
galaxy formation and evolution. I present the analysis of the UV-NIR spectroscopic and
space-based NIR imaging follow-up programs for a sample of very massive galaxy candidates
selected from wide-field ground-based galaxy surveys. ... read moreThrough the detections of nebular
emission lines, I confirm, for the first time, the existence of massive (log(M∗/M⊙) >
11.4) galaxies in the first 2 Gyrs of cosmic history (z > 3). In contrast to their
counterparts in the local universe, the very massive galaxies at 3 < z < 4 have a
diverse range of stellar ages, star-formation rates, and dust content. The analysis of the
emission-line properties and the UV-to-FIR SEDs of very massive galaxies at 3 < z < 4
reveals the presence of luminous hidden active galactic nuclei for > 80% of the sample.
I investigate the effect of AGN emission on the derived host galaxy properties, finding
that they do not considerably bias the stellar mass estimates. I investigate the structural
properties of massive galaxies (log(M∗/M⊙) > 11.2) at 1.5 < z < 3.0, increasing
the available HST imaging for this extreme population. This analysis indicates that at 2.5
< z < 3, the sizes of quiescent galaxies at (log(M∗/M⊙) > 11.2) appear to be
systematically larger than what is expected based on the extrapolation of the relation
derived from lower stellar mass galaxies, evidence for size-downsizing. Investigating the
effect of galaxy blending on the high-mass end of the stellar mass function at z > 1.5,
I find that it is most significant only for the largest stellar mass bin (log(M∗/M⊙) ≈
11.6) at 1.5 < z < 2.5. By placing strict constraints on the number densities and
formation timescales of the most massive galaxies in the early universe, these results
drive the ongoing pursuit of understanding the physical processes responsible for galaxy
formation and evolution.
Thesis (Ph.D.)--Tufts University, 2017.
Submitted to the Dept. of Physics.
Advisor: Danilo Marchesini.
Committee: Anna Sajina, Alexander Vilenkin, and Gregory Rudnick.
Keyword: Astrophysics.read less
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