Calendar

Sep
24
mar
Benoit Lavraud — Properties and processes that determine coronal mass ejection impact at planets and in the heliosphere @ Salle 306
Sep 24 @ 11 h 00 min – 12 h 00 min
Séminaire

The properties of coronal mass ejections (CME) in the heliosphere is determined by a complex chain of processes. This presentation highlights this fact by reviewing CME’s (1) intrinsic properties set at the Sun (e.g., orientation, velocity), (2) processes that may occur during eruption and propagation (e.g., shocks, confinement or magnetic erosion), and (3) in the specific interaction with the planet (e.g., magnetic properties, preconditioning mechanisms), and which together determine the CME’s actual impact. The relative importance of these processes is discussed, as well as implications at planets other than the Earth, including exoplanetary systems.

Benoit Lavraud
IRAP, CNRS, CNES, Université de Toulouse, France

Oct
8
mar
Sami DIB — The 1001 modes of Star Formation @ Univers 21
Oct 8 @ 11 h 00 min – 12 h 00 min
Séminaire

Star formation is a multi-physics, multi-scale process. the physical scales that are involved vary by 10 orders of magnitude, from the size of entire galaxies down to the size of the Solar system. The physical processes that are involved include gravity, turbulence, magnetic fields, radiation, chemical reactions, and cooling and heating processes. This multiplicity of processes and scales can generate a significant amount of variation in the outcome of star formation from galaxy to galaxy and from region to region within galaxies, in particular in terms of key quantities such as the stellar initial mass function (IMF), the star formation rate (SFR), and the star formation efficiency (SFE). I will present a brief overview of the current status of observations for the IMF and the SFR in the Milky Way and in nearby galaxies and discuss theoretical ideas and numerical simulations that attempt to reproduce these observations.

Oct
9
mer
Gregor Golabek @ Univers 21
Oct 9 @ 11 h 00 min – 12 h 00 min
Séminaire

TBD

Oct
15
mar
Jonathan Freundlich — Galaxy evolution: a gas perspective @ Univers 21
Oct 15 @ 12 h 00 min – 13 h 00 min
Séminaire

Galaxy history is marked by a peak of star formation ten billion years ago and a subsequent drop of the star formation rate (SFR) by an order of magnitude. To understand this evolution, it is crucial to probe the gas reservoirs from which stars are formed. With programs observing the molecular gas phase in typical star-forming galaxies at different epochs, I will present how the cosmic evolution of the SFR is mainly driven by that of the molecular gas fraction. The depletion time associated to star formation indeed only weakly changes with redshift, both at galactic and at sub-galactic scales. I will show that the molecular gas content during the winding-down of star formation does not seem to correlate with morphology, suggesting an ongoing supply of molecular gas to compensate for star formation while bulges grow. In contrast, molecular gas reservoirs can be dramatically depleted in extreme environments such as cluster centres. While structure formation is primarily driven by dark matter (DM) dynamics in ΛCDM cosmology, gas processes can in turn affect the DM distribution at galactic scales. Using theoretical modelling and simulations, I will discuss how outflow episodes and gas density fluctuations induced by stellar feedback can expand both the DM and the stellar distributions and hence provide a simple understanding of the formation of DM halo cores and ultra-diffuse galaxies.