Ten Billion Years of Growth: Massive Galaxy Evolution from Structures and Dynamics

by Bezanson, Rachel Shuchter, Ph.D., YALE UNIVERSITY, 2013, 159 pages; 3578313

Abstract:

Once thought to be relies of a much earlier epoch, the most massive local galaxies are red and dead ellipticals, with little ongoing star formation or organized rotation. In the last decade, observations of their assumed progenitors have demonstrated that billions of years ago, massive galaxies were more compact and morphologically different, possibly with more disklike structures. The details of this observed evolution can place constraints on the physical processes that have driven massive galaxy evolution through cosmic time.

The work presented in this thesis provides observational constraints on the dynamical and structural evolution of massive galaxies since z ~ 1.5 – 2 using a variety of photometric and spectroscopic surveys, including OBEY, SDSS, NMBS, and UDS.

First, we find that although overall densities of these galaxies have decreased with time, the central densities of massive galaxies at high and low redshifts, are quite similar. This suggests that massive galaxies grow "inside-out": compact cores form early and then gradually build a more diffuse envelope of stars in their outskirts. Balancing the need for efficient size growth and consistent number densities of progenitor and descendent galaxies, we conclude that minor-merging is the best physical explanation for the observed size evolution.

The remainder of this dissertation focuses on the inferred and measured dynamical evolution of massive galaxies since z ~ 2. Using velocity dispersions inferred by galaxy stellar masses and morphologies, we find that the number density of galaxies at a given velocity dispersion, or velocity dispersion function, is quite stable with redshift since z ~ 1.5, with a weak evolution at the low dispersion end due to a growing population of quenched galaxies. The constancy provides evidence in favor of inside-out growth of galaxies and is consistent with theoretical predictions that the central potentials of massive galaxies are set early. We suggest a toy model that requires that galaxy quenching must be extremely efficient at high velocity dispersions and quenching must be combined with rapidly increasing dispersions.

We present two large spectroscopic studies of high-redshift massive galaxies using the Keck Telescopes: directly measuring absorption line kinematics for eight galaxies at z ~ 1.5 and ~ 100 galaxies at z ~ 0.7. Using a collection of cutting edge photometric and spectroscopic data, we verify that the z ~ 1.5 galaxies are dynamically massive and compact, with high measured velocity dispersions. Surprisingly, the spectra of many of the galaxies in this sample have extremely strong Balmer absorption lines, in contrast with massive galaxies in the Universe. These observations can only be explained by recently quenched star-formation within ~ 1 Gyr.

Finally, we collect all spectroscopic data from these two surveys and ~ 6000 galaxies from the literature and examine the structural and dynamical evolution of galaxies in the Fundamental Plane since z ~ 2. We find that although the zeropoint of the luminosity fundamental plane evolves dramatically in the last 10 billion years, the mass fundamental plane exhibits very little redshift evolution. We note that a stable mass fundamental plane was predicted by simulations of merging galaxies. Finally, these results imply that galaxies must undergo evolution in their velocity dispersions, in addition to growing in size in order to remain on the Fundamental Plane.

Overall, these results provide strong evidence for inside-out growth, minimal, but non-negligible, dynamical evolution and efficient quenching of massive galaxies since z ~ 2.

AdviserPieter Van Dokkum
SchoolYALE UNIVERSITY
Source TypeDissertation
SubjectsAstrophysics; Astronomy
Publication Number3578313

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