Galaxies comic



Understanding the properties of galaxies at higher redshifts and their evolutionary pathways to present day is a very exciting and new topic, and many fascinating observations have recently surfaced on that matter. Here I show some highlights from the work done by my students and me:

Galaxies in Protoclusters at z=4

Coming soon....

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Galaxies at z = 2

Rotation curves of z=2 Magneticum Galaxies

The observations and measurements of rotation curves are an important tool in deducing the (invisible) mass of a (disk) galaxy. For the rotational velocities of the visible mass, i.e. gas and stars, a Keplerian decrease proportional to r−1/2 is expected in the outer parts of the galaxy. What is seen instead for (local) disk galaxies is that the rotation curves remain flat. This can be explained by the presence of an invisible component and thus, lead to the acceptance of the concept of dark matter.

Recently, observations of disk galaxies at high redshift (z = 2) have found that half of the gas disks exhibit declining rotation curves. This lead to the discussion whether dark matter is important, at all, and even the existence of it was put into question. In our hydrodynamical ΛCDM simulation Magneticum Pathfinder we find that about half of our disk galaxies also show declining rotation curves when calculated directly from the particle data. If we calculate the theoretical rotation curve, which takes all the mass including dark matter into account, the rotation curves remain flat. This shows that this decline is not due to the lack of dark matter; it is caused by the kinetic pressure of the gas in the disk, which is turbulent at high redshift, as the disks are in the process of forming. Interestingly, even disks in (gas-rich) elliptical galaxies have declining rotation curves, which can be important for observations, as mostly gas is used to identify disks at high redshifts. The disk galaxies with declining rotation curves evolve into disks, ellipticals and most of them into transition types.

In summary, galactic disks with declining rotation curves at high redshift emerge naturally within the ΛCDM paradigm. For more details, see Teklu et al., 2018.



Last update 24.02.2019 by Rhea-Silvia