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Accueil > Séminaires > Gas exchanges between local spirals (…)

Gas exchanges between local spirals ancestor and the intergalactic medium in the past 6 Gyrs

Myriam Rodrigues (GEPI)

I will discuss on the scenario of spiral formation as seen by the interplay between the main ingredients of the chemical evolution : metal abundance, gas mass, stellar mass and SFR. Using a representative sample of 66 intermediate mass galaxies at z ∼ 0.6, we found that galaxies had a mean gas fraction of 32% ± 3 six billions years ago, i.e. twice that of their local counterparts. Using higher redshift samples from the literature, we explore the gas-phases and estimate the evolution of the mean gas fraction of distant galaxies over the last 11 Gy. The gas fraction increases linearly at the rate of 4% per Gyr from z ∼ 0 to z ∼ 2.2. We also demonstrate for a statistically representative sample that < 4% of the z ∼ 0.6 galaxies are undergoing outflow events, in sharp contrast with z ∼ 2.2 galaxies. The observed co-evolution of metals and gas over the past 6 Gyr favours a scenario in which the population of intermediate mass galaxies evolved as closed-systems, converting their own gas reservoirs into stars. This observation consolidates a scenario where local spirales formed by the fusions of two galaxies rich in gas 6-10 Gyrs ago. In a second part, I will present the first results of the observational project ’Starfish’ (STellar Population From Integrated Spectrum). The goal of this project is to calibrate, for the first time, the properties of stellar populations derived from integrated spectra with the same properties derived from direct imaging of stellar populations in the same set of galaxies.