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Galaxies in the local Universe

Morphology of galaxies

Galaxies are typically not just uniform bodies of gravitationally bound stars and dark matter. They are made of different subcomponents such as bulges, bars, discs, nuclear clusters and halos of both stars and dark matter. In disc galaxies spiral arms often dominate the visual appearance, accompanied with filamentary patches or regular distributions of dust. Members of our group study the shape of the light profiles of galaxies, as well as the link between various substructures (or their non-existence) with other properties such as kinematics and chemistry.

 

Kinematics and Dynamics

The true or intrinsic shape of galaxies is often hidden by their projections on the sky. Are they flat discs, footballs or rugby balls of stars? Of course, in most cases they are a combination of these shapes and by imaging only it is often not possible to tell them apart. By measuring kinematics of stars and gas of nearby galaxies, via investigation of the absorption and emission-lines of spatially resolved spectra, we can determine their internal structure in much more detail. This is done in comparison with dynamical models, which based on some assumptions, provide information on the orbits of stars and motion of gas clouds. Crucially they provide us with the information on the gravitational potential and the mass of galaxies. Essential are the observations with integral-field spectrographs (IFS) which allow two dimensional mapping of galaxies. Researchers in our group use a variety of objects from purposely built IFS (PMAS, SAURON) to general user IFS of ESO (VIMOS, SINFONI).

 

Massive black holes

Massive black holes (MBH) are found in centres of most massive galaxies. They can not be seen directly, but they are conspicuous through gravitational influence on their surroundings or as powerful AGNs [link to that section]. In Milky Way, our own galaxy, we can see singles stars moving in the gravitational potential of a central MBH. In other galaxies we can not yet resolve individual stars next to the central black hole, but by measuring unresolved kinematics of stars or gas clouds, and constructing dynamical models it is possible to estimate masses of MBH. Still, it is necessary to obtain observations at the highest possible resolution and to that end researchers in our group use adaptive optics (either with laser or natural guide stars) facilities.

 

Dark matter

We can see galaxies as they are made of baryonic matter in form of dust, gas and stars, which emit electromagnetic radiation. This is, however, not all that is there. If we assume that physics laws are unchanged, galaxies also need to contain extra matter that contributes to their total mass budget. We call it dark matter, as it is not seen in electromagnetic radiation, but can be detected through kinematics of stars and gas. Research of our group focuses on the dynamical determination of dark matter content and its relations with the luminous matter in nearby galaxies (i.e. via Tully-Fisher relations).

 

Stellar populations

Galaxies are made of stars, but stars are born from gas contained within dusty clouds. What are the processes that regulate formation of stars, and how are they linked to the assembly of stars in present day galaxies? These questions can be addressed by observations of nearby galaxies, exploiting the fact that they can be spatially resolved with integral-field spectrographs. Analysing absorption-line spectra we are estimating the age of stars, their chemical content, or the abundance of chemical elements, and the history of star formation. The aim of researches in our group is to understand how stars are made and how the chemistry of the subsequent generations of stars changes as galaxies are assembled. At very early times the universe consisted mainly of Hydrogen and Helium atoms. Heavy elements, including those that we are made of (e.g. Carbon, Oxygen, Magnesium, Iron), are formed in stars during the history of the universe. Determining the abundances of the heavy elements correctly for galaxies outside our own is not an easy task. Indeed, the spectra of galaxies contain a lot of information beside the heavy element abundances. Developing new, better models that will help analyze new and better data, therefore, is part of our group research.

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