The Luminosity-Metallicity Relation of distant luminous infrared galaxies

Abstract

One hundred and five 15mu selected objects in three ISO deep survey fields (CFRS 3h, UDSR and UDSF) are studied on the basis of the high quality optical spectra with resolution R>1000 from VLT/FORS2. Ninety two objects (88%) have secure redshifts, ranging from 0 to 1.16 with a median value of 0.587. Considerable care is taken in estimating the extinction property of individual galaxy, which can seriously affect diagnostic diagrams and estimates of star formation rates and of metal abundances. Two independent methods have been adopted to estimate extinction, e.g. Balmer line ratio (A_V(Balmer)) and energy balance between IR and Hbeta luminosities (A_V(IR)). For most of the z>0.4 luminous IR galaxies (LIRGs), the two extinction coefficients are consistent well, with median values of A_V(IR) = 2.36. These distant LIRGs show many properties strikingly in common with those of local (IRAS) LIRGs studied by Veilleux et al. (1995). Our sample can provide a good representation of LIRGs in the distant Universe. Most (>77%) ISO 15mu selected sample galaxies are dominated by star formation. Oxygen abundances (12+log(O/H), derived from R23 and O32) in ISM in the distant LIRGs range from 8.36 to 8.93 with a median value of 8.67. Distant LIRGs present a metal content less than half of that of the local bright disks (i.e. L*). The Pegase2 models predict that total masses (gas + stars) of the distant LIRGs are from 10^{11} Msun to <=10^{12} Msun. 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.