Galaxies, stars and cosmology

All massive galaxies are thought to harbor a supermassive black hole (SMBH) at their center, weighing in at millions or even billions of times the mass of our Sun. SMBH depending of the quantity of matter on their vicinity are called either dormant (quiescent) for extremely low or absent accretion rates (e.g., Sgr A*, at the center of our Galaxy), or active (active galactic nuclei, AGN) for low to very high accretion rates.

The Mochima simulations is a suite of cosmological simulations using the zoom-in technique. We run simulations of the same spiral galaxy using different prescriptions to describe the baryonic physics (star formation and supernovae feedback) and show the impact on the galaxy formation and morphology as well as the consequences on the dark matter distribution in the halo and the sub-structures.
Additionnal investigation on baryonic physics modeling are in progress including AGN feedback as well as improving further star formation and supernovae feedback description.

Nunez-Castineyra et al MNRAS 2021.

https://ui.adsabs.harvard.edu/link_gateway/2021MNRAS.501…62N/doi:10.1093/mnras/staa3233

https://arxiv.org/abs/2004.06008

Cosmology is the study of the universe as a whole. We try to understand how it came into being, how it is currently growing and how it will eventually die. Over the last few decades, cosmologists have developed the so-called “Lambda CDM” standard model of cosmology, which explains the vast majority of current large-scale observations. However, this model relies on two unknown quantities: the “Lambda”, which refers to the cosmological constant, and the “CDM”, for cold dark matter. The cosmological constant is one option to explain why the expansion of the Universe is currently accelerating; other solutions would be to introduce a dark energy component or to modify the laws of gravity. Dark matter is invoked to explain gravitational interactions that are not associated with luminous matter, and could also be explained by modified gravity models. Together, the cosmological constant and dark matter account for about 95% of the energy budget of the Universe, which means that only 5% of the Universe is visible. At the Laboratoire d’Astrophysique de Marseille, we are trying to observe this dark Universe with different techniques to improve our understanding of the evolution of the Universe and to test all these alternatives to the standard model of cosmology.

Astronomy is truly undergoing a revolution in terms of its ability to monitor the temporal variability of the Universe in a continuous manner. The opening of this domain is transforming our knowledge of the evolution of the Universe, especially for objects that undergo explosive changes, such as a supernova or a gamma-ray burst. These events can release amounts of energy that have not been produced since the formation of the Universe, the Big-Bang.

We do study galaxy clusters, which are composed of up to thousands of galaxies living in a virialized structure. They constitutes the nodes of the cosmic web and carry informations about structure formation and evolution, as well as the underlying cosmological models.

These studies are observational (visible light, X-ray, SZ effect…) and theoretical (numerical simulations).

We are using space and ground based telescopes, as well as local and national supercomputers.

Several researchers in the GECO team are working on the study of individual galaxies, or small numbers of galaxies in the nearby universe, for which it is possible to obtain multi-wavelength observations that show us details of the physical processes at work in the galaxies.

This is the case, for example, of the galaxies in the Virgo cluster, where we can see the gas torn from the galaxies by the dense environment in which they reside. Deep images also allow the study of little-known classes of galaxies such as low surface brightness galaxies, or ultra-diffuse galaxies. Finally, numerical modelling of galaxy evolution is also used in the team to understand the nature of the processes at work in the formation of these galaxies, or of structures such as bars and bulges of spiral galaxies.