From instrumental design
to scientific exploitation
Home > Scientific Pole > Physics of galaxies and cosmology > News > Rodney Delgado’s thesis defense

Rodney Delgado’s thesis defense

The Evolution of the Hubble Sequence: morpho-kinematics of distant galaxies
» Monday 27 September 2010


  • François Hammer (Observatoire de Paris)
  • Hector Flores (Observatoire de Paris)

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, and has the main advantage of
presenting a good correlation between the morphological type and dynamical
state of each galaxy.

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, which provides a complete kinematic diagnosis, 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 classification to a representative sample of
galaxies at z ≈ 0.6, we found that 4/5 of spiral galaxies are rotating
disks, while more than 4/5 peculiar galaxies are not in a dynamical

Present-day Hubble sequence derived from our local sample and past Hubble
sequence derived from our distant sample. Each stamp represents
approximately 5% of the galaxy population (Delgado-Serrano et al., 2010).

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. We
found that spiral galaxies were 5/2 times less abundant in the past, which
is compensated exactly by the strong decrease by a factor 5 of peculiar
galaxies, while the fractional number of elliptical and lenticular
galaxies remains constant. It strongly suggests 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. In the
coming years, our morphological classification and these studies will be
extended to galaxies at z >> 1, thanks to the future ELTs.

To read