Résumé / Abstract Seminaire_IAP
« A chemical Universe. Gas, metals, and cosmic dust in local and distant galaxies  »

Annalisa De Cia
Département d'Astronomie, Université de Genève (Genève, Suisse)

The chemical composition of the Interstellar Medium (ISM) is key for the evolution of stars and galaxies throughout cosmic time. The metal content of the neutral gas in galaxies can be probed in great detail with absorption-line spectroscopy of stars in the Local Group, or distant quasars and gamma-ray bursts (GRBs). However, the presence of dust dramatically alters the metal abundances observed in the neutral ISM, because of the depletion of metals into dust grains. I developed a technique to characterise dust depletion, based on the relative abundances, because different metals deplete into dust grains at different rates. This is key for a deeper understanding of the chemical content of the neutral ISM. In this talk, I will focus on these three discoveries: 1) Large metallicity variations in the neutral ISM in the Galaxy, which was hitherto assumed to be chemically uniform. This suggests the accretion and inefficient mixing of pristine gas on the Galactic disk. 2) The cosmic chemical evolution of the neutral ISM. After taking dust corrections into account, the evolution of the neutral ISM metallicity shows three times more metals than previously estimated. This leads to the fact that the neutral ISM carries the majority of metals at high z. 3) Peculiar metal content in very distant galaxies. A strong overabundance of aluminium (and possibly a hyper enhancement of ?-elements) is observed in the two GRBs at z = 6 with quality spectra available so far, suggesting that very massive stars may play an important role for the chemical enrichment of the early Universe.
vendredi 6 mai 2022 - 11:00
Amphithéâtre Henri Mineur, Institut d'Astrophysique de Paris
Page web du séminaire / Seminar's webpage