This thesis focuses on the study of atmospheres of main sequence cool stars (spectral types G2V, K0V, and M2V, with solar metallicity) by means of three-dimensional time-dependent magneto-hydrodynamic simulations of their near-surface convection and photospheres. The simulations are computed with the MANCHA code, which is adapted to simulate other

One of the main goals of the NASA Transiting Exoplanet Survey Satellite (TESS) mission is the discovery of Earth-like planets around nearby M-dwarf stars. We present the discovery and validation of three new short-period Earth-sized planets orbiting nearby M dwarfs: TOI-5720 b, TOI-6008 b, and TOI-6086 b. We combined TESS data, ground-based

Ultra-diffuse galaxies (UDGs) are attractive candidates to probe cosmological models and test theories of galaxy formation at low masses; however, they are difficult to detect because of their low surface brightness. In the Local Group a handful of UDGs have been found to date, most of which are satellites of the Milky Way and M31, and only two are

Models predict that water-rich planets may be common around low-mass stars, but definitive evidence for the existence of water worlds has remained elusive. Recent JWST observations of sub-Neptune sized planets orbiting nearby M dwarfs found atmospheres enriched in CH4, CO2 and H2O, but the enrichment mechanism is debated. To answer this question

Context. Number counts of galaxy clusters across redshift are a powerful cosmological probe if a precise and accurate reconstruction of the underlying mass distribution is performed - a challenge called mass calibration. With the advent of wide and deep photometric surveys, weak gravitational lensing (WL) by clusters has become the method of choice

Recent observational studies suggest that feedback from active galactic nuclei (AGNs) may play an important role in the formation and evolution of low-mass dwarf galaxies, an issue that has received little attention from a theoretical perspective. We investigate this using two sets of 12 cosmological magneto-hydrodynamical simulations of the