Observational constrains on the chemical evolution of high redshift galaxies through 3D spectroscopy.

In this thesis I investigate the properties of 34 star forming galaxies at z ~3.4, by exploiting data obtained with the VLT near-infrared integral field spectrometer SINFONI. By using the SINFONI spectra, along with multi-band photometric images, I investigate the metal content, dynamics and star formation in these galaxies. One of the most important results is that z~ 3.4 galaxies deviate from the scaling relations between mass, star formation rate and metallicity characterizing local and low redshift galaxies (z<2), in the sense that galaxies at z>3 are characterized by metallicities significantly lower. This deviation occurring only at z>3 must trace a different galaxy evolutionary mechanism in place at such early epochs, with respect to galaxies at 0<z<2. However, I show that the deviation from the local scaling relations is not associated with dynamics of the host galaxy (rotating disks and mergers/interacting galaxies deviate by the same amount), hence an increased rate of merging cannot be responsible for such deviations. By using the integral field spectroscopic information I could map the metallicity in a subsample of 10 galaxies at z ~3.4. These are among the first metallicity gradients measured at such high redshift. We find that a significant fraction of galaxies are characterized by inverted (positive) metallicity gradients, i.e. the metallicity increases towards the outer regions, in contrast to what observed locally. Also for what concerns the metallicity gradients, I found that the occurrence of inverted gradients is not correlated with the galaxy dynamical properties. A more detailed investigation reveals that the metallicity anticorrelates with the star formation rate, which peaks in the central region of galaxies. This result supports the models of smooth gas inflows feeding galaxies at high redshift. In this scenario the pristine infall both boosts star formation (through the Schmidt-Kennicutt law) and dilutes the metallicity, generating the observed anti-correlation. By mapping the distribution of the star formation, and by inverting the Schmidt-Kennicutt relation, I could also infer the distribution and total content of molecular gas in these z~ 3 galaxies. I found evidence that the average gas fraction in galaxies at z>3 does not follow the steep increasing evolution from z=0 to z ~2. Between z~ 2 and z~ 3 the average gas fraction in galaxies remains constant or, possibly, even decreases. Our findings are marginally consistent with the models expectations on the evolution of the gas content in galaxies and further support the scenario that the evolution of cosmic star formation in galaxies is primarily driven by the evolution of the amount of gas in galaxies, and not by an evolution in the efficiency of star formation. By combining the information on the gas content and on the metallicity I could infer the galaxy properties can only be explained by a combination of massive inflows and massive outflows, both of which a factor of few to several higher than in the host galaxy. Such massive flows in the early universe are likely responsible for the different properties and deviations of galaxies at z 3 relative to local and low redshift galaxies. I further explore the physical mechanisms driving galaxy formation and evolution by comparingmy observational results with detailed semi-analytical models and cosmological simulations specifically developed, in collaboration with other teams, to trace the metallicity evolution and distribution in early galaxies.