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novembre 2017
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No seminar — Fall break

Vendredi 3 novembre 11:00-12:00

Jens Chluba (Manchester) — Cosmology Beyond Thermal Equilibrium : Future Steps with CMB spectral distortions

Vendredi 10 novembre 11:00-12:00 - Amphi

Since the measurements with COBE/FIRAS in the mid-90’s we know that the energy spectrum of the cosmic microwave background (CMB) is extremely close to that of a perfect blackbody. However, a number of early Universe processes should create spectral distortions at a level within reach of present day technology. I will give a broad-brush overview of recent theoretical and experimental developments, explaining why future measurements of the CMB spectrum will open an unexplored new window to early-universe and particle physics. This provides an exciting new path forward in CMB cosmology which is complementary to planned and ongoing searches for primordial B-mode polarization signals. I will also highlight some of the challenges due to foregrounds.

Mathieu Puech (GEPI) — Rotating discs vs. mergers at z 1 : is there really a disc survival issue in LCDM ?

Vendredi 17 novembre 11:00-12:00 - Amphi

Discs represent 70% of local massive spirals. Such a large fraction has been suggested to be in tension with the relatively high occurrence rate of major mergers at higher redshifts in LCDM, which has been dubbed as the "disc survival issue". Observations of the spatially-resolved kinematics and the high resolution morphology of their progenitors at z=0.6-1.2 suggest that gas-rich mergers is a viable solution to this issue. I will review observational evidences for this with a particular focus on the counter-arguments that have been discussed in the community, e.g., the existence of a main sequence of star forming galaxies, the large fraction of (U)LIRGs with spiral morphologies, the low fraction of the SFR attributed to major mergers, or the large fraction of spiral galaxies with no classical bulges (ie, pseudo-bulges and bulgeless). I will show that none of these arguments are actually valuable counter-proofs of the prominent role of gas-rich major mergers in shaping a large fraction of local spiral galaxies. Finally, I will discuss the current and future reliability of rotation curve measurements in distant galaxies, focusing in particular on MOSAIC, the future ELT multi-object spectrograph.

Olivier Absil (Liege) — Five years of harvest with the vortex coronagraph

Vendredi 24 novembre 11:00-12:00 - Amphi

While the concept of vortex coronagraphy dates back to 2005, the first science-grade Annular Groove Phase Masks (AGPM), working in the thermal infrared regime, have been installed at the VLT only in 2012. They are now also equipping the Keck telescope and the Large Binocular Telescope, and will soon be at the core of more ground-based high-contrast imaging instruments. In this seminar, I will shortly review the technology development undertaken over the last 12 years, and describe the on-sky operations and performance of the vortex coronagraph. I will then present the main scientific results obtained since 2012, and explain how we have recently adapted deep learning techniques to the problem of post-processing in high-contrast imaging. I will finally discuss the perspectives with new instruments, including the Breakthrough Watch project.

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