Valentin Perret - March 21, 2014

Mergers of teenage galaxies: from simulations to observations

Understanding the mechanisms of formation and evolution of galaxies in a
cosmological context remains a major challenge in modern astrophysics.
Especially, the contribution of the fusion processes to the cosmological mass
assembly is still poorly understood. In this context, the study of the dynamical
support of galaxies is a way to constrain different evolution scenarios. In this
seminar, I will present the major results of my thesis focused on interactions
of young galaxies. I will introduce first my contribution to the kinematical
analysis of the MASSIV sample composed of 83 young galaxies (1<z<2) observed
with the integral field spectrograph SINFONI at the VLT. Thanks to the use of a
method based on a spherical harmonics decomposition of velocity fields, I
defined an analysis and an automatic classification technique that aims at
quantifying the fraction of objects that are likely to be the product of a
recent galaxy merger. I will present afterwards a method to build initial
conditions of idealized galaxies, prerequisite to the hydrodynamic modelling of
young galaxies in interaction. Using this technique, I will then talk about the
definition and analysis of the sample of idealized simulations MIRAGE, whose
initial conditions are designed to reproduce the physical properties of the most
gas-rich young galaxies. This sample which required about 3.5 million hours CPU
time, is composed of 20 simulations of mergers exploring the initial parameters
of mass and orientation of the disks with a spatial resolution reaching 7
parsecs and modelling many physical processes. The simulations show in
particular the absence of a star formation bursts in mergers of fragmented and
turbulent disks, suggesting a saturation mechanism. An analysis of the
properties of clumps that are generated by gravitational instabilities will be
presented subsequently, highlighting the compatibility of long-lived clumps
scenarios with observations in terms of outflowing material and stellar
population ages. I will also underline that the gas rich clump fusion mechanism
is able to control the bulge mass growth, to erode the central profile of the
dark matter halo and to drive massive gas outflows in the disk plane. Finally, I
will end this talk by presenting a comparative study of the MASSIV kinematical
data to a set of more than 4000 pseudo-observations at z=1.7 built from
simulations of the MIRAGE sample to determine the ability to detect galaxy
merger signatures under the observational conditions of the SINFONI instrument.