The Emergence of Bulges and Disks in the Universe

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 (DEV-ILS) 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 (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 (∼ 40%), 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 ∼ 50% of the total stellar mass of the Universe at all epochs is in disk structures with this contribution relatively unchanged since z ∼ 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 an epoch when pseudo-and classical-bulges are emerging. Finally, the M * − R e relations of galaxies and their components show that different components follow distinct relations which may reflect their distinct evolutionary pathways through which these systems have been built.The evolution of the M * − R e relations of galaxies and their components shows minimal variation. The unchanged scaling relations since z = 1 is consistent with the evolution along the M * − R e trends.

Multiwavelength Bulge–Disk Decomposition for the Galaxy M81 (NGC 3031). I. Morphology

“…The variation in the morphology of bulges with wavelength provides an interpretation of the inconsistency between observations of high-redshift galaxies and modeling of galaxy evolution. It has been reported that bulges are predicted to have been formed at the redshift z ∼ 2, but galaxies at z = 1-3 are found to be mainly dominated by disks (van Dokkum et al 2013;Bruce et al 2014;Shibuya et al 2015;Toft et al 2017;Dimauro et al 2019;Tacchella et al 2019;Hashemizadeh 2022). In practical terms, for high-redshift galaxies, optical telescopes observe their rest-frame UV appearances.…”