Kinematical Properties of Galaxies
This is work done by my students Felix Schulze and Adelheid Teklu on the kinematical properties of galaxies in comparison to modern IFS surveys and the angular momentum and spin properties of galaxies.
Inner Kinematics of Early Type Galaxies
The formation and evolution of galaxies is still unknown in many aspects.
The complex interplay between baryonic processes and the hierarchical structure
formation of dark-matter halos is still a highly-debated research topic.
Several recent studies using novel observational techniques, especially
integral-field spectroscopy, suggest that the formation history, and thus
the closely related in- and outflow of matter, is encoded in the stellar
kinematics of galaxies.
During the hierarchical assembly of dark-matter halos within the ΛCDM
framework, dominant processes like stripping, harassment, and galaxy mergers
leave an imprint in the present-day kinematics of early-type galaxies (ETGs).
Physical effects like dynamical friction and violent relaxation during these
processes are capable of drastically modifying the statistical distribution of
orbits, while triggered star-formation and accretion of fresh gas builds up
new cold components.
Pioneering studies conducted during the past decade showed that, in contrast
to the general expectation, ETGs come in two flavours:
fast-rotating ETGs exhibit a regular rotating line-of-sight velocity pattern,
while slow-rotating ETGs show more complex inner velocity structures leading
to a increased velocity dispersion.
In a more refined distinction, velocity maps can display multiple internal features
like distinct cores, counterrotating components, or even prolate rotation.
Those features represent strong constraints on the formation pathways
that have to be taken into account by a generic theory of galaxy formation.
During the past decade the quality in terms of resolution and implemented physics in cosmological simulations
has made a major step forward producing a galaxy population with realistic kinematic properties (see
Van de Sande et al. (2019)
for a comprehensive comparison). These simulations represent a powerful tool to investigate the physical
processes, and their complex interplay, that lead to the galaxies observed today.
See
Schulze et al. (2017) for more information about kinematic properties and lifetimes of young KDCs,
and
Schulze et al. (2018) for more information on the statictical properties of early-type galaxies in the
fully hydrodynamical cosmological simulation Magneticum, including a study on the connection of kinemtical features in the velocity maps and global kinematical parameters.
· · · ·
Global Spin
The formation of galaxies, especially how the different types of galaxies have
formed, has been discussed for a long time and is still not fully understood.
In this context, the evolution and the distribution of angular momentum is
of special interest, as the angular momentum of the visible matter –
under the assumption of angular momentum conservation – should carry
the information of the underlying dark-matter halo.
Since our simulation self-consistently produces disk-like galaxies
as well as spheroidal galaxies, we can study the connection between
the kinematical properties like the angular momentum, and the
morphology of the galaxies and compare them to observations; in the
so-called stellar mass–stellar specific angular momentum plane
(M∗–j∗ plane)
our simulated galaxies agree well with observations
by Fall & Romanowsky (2013).
When we look at the global spin parameter λ, which
includes all the mass (dark matter and baryons) within the virial
radius, we find that the spheroidal galaxies live in halos that have
a lower median spin than those of the disk galaxies.
Even in the dark-matter-only run, which is the same run without baryons, we
find that the galaxies identified in the baryon run as disks have a higher
median spin than those identified as spheroids.
This, taken together with the fact that we nevertheless find spheroids
with high λ values, suggests that the formation history and
the environment simultaneously shape the halo and the type of
the galaxies inside the halo.
For more information, see
Teklu et al., 2015 and
Teklu et al., 2016.
|