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mai 2019
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John Carter (Institut d’Astrophysique Spatiale) - The water story of Early Mars through compositional remote sensing : lessons learned and future prospects for exploration

Vendredi 3 mai 11:00-12:00

Water on early Mars has left chemical fingerprints which survive today as secondary "aqueous" minerals : clays, salts and other species. Their study allows piecing together the geochemical conditions on early Mars, to trace the potential past habitability of the planet and its ability to have sequestered organic matter over geologic time scales. The pervasive processes of water - rock interactions preserved at Mars are also a window into Hadean Earth, a period when conditions are thought to have been conducive to life but of which the record has been obliterated. Aqueous minerals are also prospective resources for future human missions to Mars. Since their discovery 15 years ago, a large diversity of mineral phases and geologic contexts have been found, but Mars has been slow to reveal its secrets. It is still not understood what the dominant mode of alteration was, if it was connected to a hydrological cycle as on Earth, and its potential for organic matter evolution and preservation. Future missions and instrument concepts are being prepared which will allow refined in-situ studies of the aqueous mineralogy and search for associated organics.

Serena Viti (UCL) - Characterizing the dense gas in galaxies

Vendredi 10 mai 11:00-12:00

It is now well established that chemistry in external galaxies is rich
and complex. In this talk I will give an
overview of the field of Astrochemistry, with special emphasis on its
relevance to extragalactic studies.
I will show how molecules play a key role in the formation and shaping
of galaxies. By using examples from different
regions of space, from starburst regions, to gas surrounding AGNs, I
will demonstrate how
important molecules are for the characterization of galaxies. Finally I
will present a new approach for the
interpretation of molecules using Bayesian and Machine Learning
techniques.

Francesco Pepe (Geneva) - ESPRESSO - High-fidelity spectroscopy with the VLT

Vendredi 17 mai 11:00-12:00

ESPRESSO has started operations at the VLT on October 2018. It is the first HARPS-like spectro-velocimeter installed on a 10-m class telescope and able to collect incoherently the light of up to 4-UTs simultaneously, exploiting thus the collecting area of an equivalent 16-m telescope. ESPRESSO is designed for ultra-precise Doppler measurements and high-fidelity astronomical spectroscopy, and aims at searching and characterizing rocky extra-solar planets in the habitable zone of solar-type stars. The planet Proxima Cen b, which was recently discovered with HARPS, is a foretaste of what may be possible with ESPRESSO, but the high spectroscopic fidelity of ESPRESSO will also allow us to do transit spectroscopy of exoplanets, study the RM effect on faint objects, performing stellar spectroscopy in the milky way and in neighbouring galaxies, study the variability of physical constants, etc. In my talk I will describe the ESPRESSO instrument, its science drivers, and preliminary performances and results from the Commissioning and the first observation period.

Lutz Wisotzki (Leibniz Institut für Astrophysik Potsdam AIP) - The high-redshift universe in Lyman-alpha emission

Vendredi 24 mai 11:00-12:00

Lyman-alpha radiation is a natural signature of star-forming galaxies and has been used since long to identify high-redshift objects. I present observations with the MUSE instrument at the ESO-VLT that have revealed more than 1000 Lyman-alpha emitters, some of them extremely faint. Moreover, we find ubiquitous extended Ly-alpha emitting envelopes around individual normal (non-AGN) galaxies at redshifts z > 3. These Ly-alpha haloes indicate huge reservoirs of cold gas in the circumgalactic medium. At the sensitivity level reached by MUSE, a large fraction of the field of view is actually covered with Lya emission from redshifts 3 < z < 6. The corresponding cross-sections are comparable to those of high-column density hydrogen absorbers, suggesting that most atomic hydrogen at these redshifts has now also been detected in emission. Our observations provide direct insights into the spatial distribution of at least partly neutral gas in the circumgalactic medium of low mass galaxies at z > 3. I also discuss some implications for the demographics of high-redshift galaxies.

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