The Emergence of Bulges and Disks in the Universe

TL;DR

This study analyzes the morphological evolution of 44,000 galaxies up to redshift 1 using HST imaging, revealing how stellar mass and structures like disks and bulges have grown over cosmic time.

Contribution

It provides one of the largest morphological classification and structural analysis catalogs, quantifying the evolution of galaxy types and stellar mass distribution over time.

Findings

One-third of the Universe's stellar mass formed in the last 8 Gyr.

Elliptical systems dominate the high-mass end growth.

Disks and bulges together contain about 50% of the stellar mass at all epochs.

Abstract

This thesis makes use of the imaging data from the Advanced Camera for Surveys (ACS) of the Hubble Space Telescope (HST) in the Cosmic Evolution Survey (COSMOS) and the Deep Extragalactic VIsible Legacy Survey (DEVILS) field. We provide visual morphological classifications of 44,000 galaxies out to redshift $z = 1$ and above a stellar mass of $10^{9.5} M_\odot$ (D10/ACS sample). We perform a robust Bayesian bulge-disk decomposition analysis of the D10/ACS sample. This study forms one of the largest morphological classification and structural analyses catalogues in this field to date. Using these catalogues, we explore the evolution of the stellar mass function (SMF) and the stellar mass density (SMD) together with the stellar mass-size relations ($M_*-R_e$) of galaxies as a function of morphological type as well as for disks and bulges, separately. We quantify that one-third of the current stellar mass of the Universe was formed during the last 8 Gyr. We find that the moderate growth of the high-mass end of the SMF is dominated by the growth of elliptical systems and that the vast majority of the stellar mass of the Universe is locked up in disk+bulge systems at all epochs and that they increase their contribution to the total SMD with time. The contribution of the pure-disk morphology gradually decreases with time ($\sim40\%$), while ellipticals increase their contribution by a factor of $1.7$ since $z = 1$. By decomposing galaxies into disks and bulges we quantify that on average $\sim50\%$ of the total stellar mass of the Universe at all epochs is in disk structures with this contribution relatively unchanged since $z \sim 0.6$. With this comes more rapid growth of pseudo-bulges and spheroids (bulges and ellipticals) in mass. Furthermore, while the cosmic star-formation history is declining the Universe is transitioning from a disk dominated era to ...