Galaxy "breathing" and the lack of metallicity evolution through the cosmic epochs

Séminaire IPAG de Robert Maiolino (OAR, Roma) jeudi 26 mai 2011 à 11h00, IPAG seminar room

I will initially review the metallicity properties of local galaxies and present clear evidence that they follow a relatively tight relation between metal content, stellar mass and star formation rate. This tight relation suggests a long standing equilibrium between star formation and galaxy "breathing", i.e. inflow of pristine gas and outflow of enriched gas. However, the most interesting result is that even galaxies at high redshift out to z 2.5 follow the same relation. This result indicates that galaxies do not really evolve in terms of formation mechanism, at lest within the redshift interval 0

I will discuss the implications of this result within the context of the cosmic evolution of the gas content in galaxies and of the cosmic star formation rate as a function of redshift. However, evolution in terms of metallicity is actually observed at z>3, where massive galaxies are found to be metal poor relative to the local relation. Hence, the first 2 Gyr of life of the universe (z>3), may actually be the first epoch characterized by real galaxy evolution, in terms of different formation processes. Detailed, spatially resolved observations of these high-z galaxies suggest that such evolution at z>3 is at least partly due to an excess of pristine massive gas inflow at these early epochs. Alternatively, extremely powerful (metal rich) outflows, possibly driven by nuclear accreting black holes, my be responsible for such a metallicity deficit. Within this context I will also discuss some very recent observational evidences for such massive gaseous outflow taking place.