The metallicities of Luminous Infrared Galaxies at z∼ 0.7, hints to the evolution of galaxies

A sample of distant (z>0.4) luminous infrared galaxies (lirgs) selected from isocam deep survey fields (cfrs, udsr, udsf) have been studied on the basis of their high-quality optical spectra from VLT/fors2 (r=5å). Robust estimates of dust extinction can be considered via the energy balance between the infrared and hβ luminosities, after correcting the underlying balmer absorption properly. Oxygen abundances [12+log(o/h)] in the interstellar medium of the sample galaxies estimated from the "strong-line" method show a range from 8.36 to 8.93, with a median value of 8.67, which is 0.5 lower than that of local bright disks (i.e. l^*) at the given magnitude. The timescale to double the stellar masses of such lirgs can be very short, 0.1-1 gyr. A significant fraction of distant large disks are indeed lirgs. Such massive disks could have formed ∼50% of their metals and stellar masses since z∼1.