The Evolution of the Hubble Sequence: morpho-kinematics of distant galaxies

TL;DR

This study introduces a new morphological classification method for galaxies, enabling a reliable comparison of the Hubble sequence over the past 6 billion years by integrating kinematic and morphological data.

Contribution

The paper presents a novel, reproducible morpho-kinematic classification method that improves the understanding of galaxy evolution and the Hubble sequence over cosmic time.

Findings

Over half of present-day spirals had peculiar morphologies 6 Gyr ago.

The distant baryonic Tully-Fisher relation shows no evolution over 6 Gyr.

The new classification correlates better with galaxy kinematics than previous methods.

Abstract

The main objective of my thesis was to provide us, for the first time, with a reliable view of the distant Hubble sequence, and its evolution over the past 6 Gyr. To achieve this goal, we have created a new morphological classification method which (1) includes all the available observational data, (2) can be easily reproduced, and (3) presents a negligible subjectivity. This method allows us to study homogeneously the morphology of local and distant galaxies. The first step has been to study the evolution of galaxies using the IMAGES survey. This survey allowed us to establish the kinematic state of distant galaxies, to study the chemical evolution of galaxies over the past 8 Gyr, and to test important dynamical relations such as the Tully-Fisher relation. The information gained from kinematics is, indeed, crucial to guarantee a robust understanding of the different physical processes leading to the present day Hubble sequence. Using Integral Field Spectroscopy, we have been able to test our new morphological classification against the kinematic state of each galaxy. We found that the morpho-kinematic correlation is much better using our classification than other morphological classifications. Applying our morphological classification to a representative sample of both local and distant galaxies, having equivalent observational data, we obtained a Hubble sequence both in the local and distant Universe. Our results strongly suggest that more than half of the present-day spirals had peculiar morphologies, 6 Gyr ago. Finally, I present further studies concerning the history of individual galaxies at z < 1, combining kinematic and morphological observations. I also present the first ever-estimated distant baryonic Tully-Fisher relation, which does not appear to evolve over the past 6 Gyr.