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février 2014
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Vendredi 7 février 2014 11:00-12:00

Seminar by Eric Josselin CANCELLED

Matthieu Béthermin (CEA Saclay) — Understanding the High-z, Dusty, Star-Forming Galaxy Populations

Jeudi 13 février 2014 11:00-12:00 - Amphi

Abstract : The star formation rate (SFR) density was more than 10 times higher at z=2 than nowadays. In addition, the star formation was dominated by objects forming 100Msun/yr. This strong evolution is very difficult to explain with physical models. Observations and phenomenological models can thus provide crucial insights to explain this. I will review the new results obtain using a new modeling approach called 2SFM (2 star-formation mode). This modeling approach is based on the existence of a strong correlation between the stellar mass and the SFR, so-called main sequence, suggesting that the bulk of the star formation in the galaxies is driven by secular processes. However, a second population of major-merger-driven starburst, with a boosted star formation efficiency, is necessary to explain the most extreme objects.

This approach is very efficient to reproduce a large number of statistical observables as the infrared luminosity functions and the number counts of galaxies from the mid-IR to the radio assuming just a set of observed scaling laws. With few extra assumptions concerning the relation between the dust attenuation and the stellar mass, we are also able to reproduce the UV luminosity functions. We also extended this model to predict the link between the dark matter halos and the star-forming galaxies using a technique of abundance matching, and managed to reproduce the fluctuations of the cosmic infrared background, measured by Planck and Herschel and caused by the fact that star-forming galaxies follow the large-scale structures. In this paradigm, the strong evolution of star-forming galaxies can be explained by an universal halo mass where the star-formation is the most efficient and the evolution of the accretion into halos at this mass. This model also agrees well with our new extensive study of the clustering of UV- and FIR-selected at z=2 as a function of their physical properties, which also provide interesting constraints on the nature of starbursts and the mechanisms of quenching of galaxies at high redshift and. Finally, I will present new results on the evolution of the mean infrared SEDs of main-sequence galaxies and starbursts up to z=4 and the consequences on their dust and gas content. These results suggest that the main causes of the evolution of the star formation at high redshift is the presence of massive reservoirs of gas, rather than an evolution of the star formation efficiency.

Simone Esposito (Arcetri) — Observing at LBT : the power of Adaptive Optics

Vendredi 21 février 2014 11:00-12:00 - Amphi

Abstract : The LBT is a unique telescope featuring two co-mounted optical trains with 8.4m primary mirrors. The telescope First Light Adaptive Optics system (FLAO) uses two innovative key-components namely an adaptive secondary mirror with 672 actuators and a high order pyramid wavefront sensor. On sky operations demonstrated that such a system reached performance never achieved before on a ground based large optical telescope. Images with 40mas resolution, Strehl-Ratio (SR)>90% and contrast around 10^4 has been acquired in H band (1.6 um). In the seminar after describing shortly the LBT telescope main features and the FLAO system and its commissioning I will present some scientific results achieved in SDT AO mode like exoplanets imaging (HR8799), CMD of crowded globular clusters regions (M92, M15), high resolution astrometry of theta 1 Ori cluster in Trapezium region. Finally I will summarize the proposed future developments of LBT AO systems and instrumentations.

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