A Mean Field View on Geodynamo Models

By Martin Schrinner

Room D18 (2e étage) à l'ENS, 24 rue Lhomond, 13:00 à 13:45

The S3 databases and an application to the detection of HI at high redshift with the SKA

By Francois Levrier

Room D18 (2nd floor) at ENS, 24 rue Lhomond, 13:00 to 13:45

The S3 (SKADS Simulated Sky) databases are a set of continuum and HI simulations of the radio sky performed at the University of Oxford. The purpose of these simulations is to provide the community a common testing ground for many of the SKA key science projects, as well as for instrument design issues on the way to the SKA. Consequently, they also form an ideal set of simulated skies to plan deep radio surveys with SKA pathfinders.

I will first present the architecture of these databases, the web portal that was implemented in collaboration with the Oxford e-Research Center (OeRC), through which access to the data is granted, and our efforts to integrate this research into a virtual observatory (VO) framework.

I will also present the tools that were designed to generate maps and cubes out of the database records, and our first use of these tools in the assessment of the detectability of HI at z > 0.3 with different SKA configurations.

Relativistic jets in GRB and radio galaxies FRI, FRI

By Zakaria Meliani

Room D18 (2nd floor) at ENS, 24 rue Lhomond, 13:00 to 13:45 In the first part, I will present the numerical investigation of the various evolutionary phases in the interaction of a relativistic shell with its surrounding cold Interstellar Medium (ISM). We do this for both 1D isotropic as well as full 2D jetlike fireball models. In such jetlike GRB models, I will discuss the differences with the 1D isotropic GRB equivalents. These are mainly due to thermally induced sideways expansions of both the shocked shell and shocked ISM regions. We found that the propagating 2D ultrarelativistic shell does not accrete all the surrounding medium located within its initial opening angle. Part of this ISM matter gets pushed away laterally and forms a wide bow-shock configuration with swirling flow patterns trailing the thin shell. The resulting shell deceleration is quite different from that found in isotropic GRB models. The second part, We will expose different model of jet deceleration in FRI radio galaxy. The first, we study relativistic jet propagation in radio galaxies, where the jets encounter a sudden jump in the external medium density. We use this setup to analyze the deceleration of jets in FR I radio galaxies, where the jet is relativistic at $pc$ scales, and subrelativistic at $kpc$ scales. Variations in ISM density could explain sudden transitions in jet propagation behavior. The second, We explore the stability of stratified, rotating, relativistic two-component jets, in turn embedded in static interstellar medium. Also we analyze the effects of two-component in jet deceleration. In the end, I will present the effects of the helical magnetic field on the jet stabilization and the formation of the cocoon.