Laboratoire d’Études du Rayonnement et de la Matière en Astrophysique et Atmosphères

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Terahertz Instrumentation and Remote Sensing

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It includes research activities in three directions:
- Terahertz instrumentation for ground-based and space telescopes
- Earth remote sensing using multiple satellite observations
- data processing and virtual observations

The Instrument group at LERMA is a key international player in milllimeter to THz components and instrumentation, with active participation in space borne missions within international collaborations. Its main goal is to advance basic knowledge in THz devices, and to develop new technologies or circuit concepts in order to be able to propose some instruments as PI or as a key partner. This group has always worked at the frontier of electronics in terms of frequency and sensitivity. It is specialized in millimeter to THz heterodyne components and receivers, which provides unique insight in the physics and chemistry, in particular of the interstellar medium and the atmosphere of planets, including the Earth.

The Software Instrumental activity of this pole focuses on the modeling of the instrumentation, the processing of the data, and the development of Virtual Observation strategies. The data come both from instruments (e.g., ALMA, NOEMA, Planck, SKA) and from numerical simulations. The activity includes all the aspects and problems related to data consolidation, data storage and perpetuation, data diffusion and sharing.

The Earth and Planet Remote Sensing component revolves around the microwave to millimeter wave radiometry from satellites, for the characterization of the Earth atmosphere and surface. Different aspects are covered, including the analysis of satellite observations, the modeling of the radiative transfer, and the development of inversion methods. It is based on collaboration with the instrument group and projects couple science and instrument studies. The group works on both atmospheric and surface analysis, using microwave observations but also exploring the synergies between visible, infrared and microwave observations. We produce geophysical variables (e.g., soil moisture, inundation extent, emissivity) over long time series at a global scale, or for use by the climate and meteorological communities. We are also involved in the analysis of satellite observations of planet, using similar methodologies.

Séminaires à venir

Vendredi 22 janvier 2021, 14h00
via Zoom , Paris
Dark matter halo response to baryons
Observatoire astronomique de Strasbourg
résumé :
While cold dark matter numerical simulations predict steep, `cuspy' density profiles for dark matter halos, observations favour shallower `cores'. The introduction of baryonic physics alleviates this discrepancy, notably as feedback-driven outflow episodes contribute to expand the dark matter distribution for stellar masses between 10^7 and 10^10 Msun. I will first present a parametrization of dark matter halo density profiles with variable inner slope and concentration that enables to describe the variety of halo responses to baryons and has analytic expressions for the gravitational potential, the velocity dispersion, and lensing properties. This parametrization provides a useful tool to study the evolution of dark matter haloes, to model rotation curves of galaxies and gravitational lenses, and to be implemented in semi-analytical models of galaxy evolution. I will then present two theoretical models describing core formation in dark matter haloes. In the first one, sudden bulk outflows induced by stellar feedback reorganise the halo mass distribution while it relaxes to a new equilibrium. In the second one, small stochastic density fluctuations induce kicks to collisionless particles that progressively deviate them from their orbits. Both models are tested against numerical simulations and provide a simple understanding of the transition from cusps to cores by feedback-driven outflows.
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