The Luminosity-Metallicity Relation of Distant Luminous Infrared Galaxies Yanchun Liang (1,2), Francois Hammer (2), Hector Flores (2), David Elbaz (3), Delphine Marcilla (3),Licai Deng (1),Catherine J. Cesarsky (4) (1) National Astronomical Observatories, Chinese Academy of Sciences, Beijing, China; (2) GEPI, Observatoire de Paris-Meudon, Meudon, France; (3) CEA, Saclay-Service d'Astrophysique, Orme des Merisiers, F91191 Gif-sur-Yvette Cedex, France; (4) ESO, Karl-Schwarzschild Strase 2, D85748 Garching bei Munchen, Germany Abstract: A large sample (64 of the 105 objects) 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, including the dust extinction, diagnostics, star formation rates and metallicities in interstellar medium etc. The extinction coefficients estimated from two independent methods, e.g. Balmer line ratio (A V (Balmer) )and energy balance between infrared and H  luminosities (A V (IR)), are consistent well, with median value of These distant LIRGs show many properties (IR luminosity, continuum color, ionization and extinction) strikingly in common with those of local (IRAS) LIRGs studied by Veilleux et al. (1995) (V95). They can provide a good representation of LIRGs in the distant Universe. Oxygen abundances in interstellar medium (12+log(O/H)) in the sample galaxies have been estimated from the extinction corrected “strong” emission line ratios, and shown a range from 8.36 to 8.93 with a median value of 8.67, which is half lower than that of the local bright disks (i.e. L*) at the given magnitude. The Pegase2 models predict that total masses (gas + stars) of the distant LIRGs are from M  to  M . 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. Conclusion:This is by far the largest sample of optical spectra of distant LIRGs. Their A V (Balmer) and A V (IR) are consistent well. These distant LIRGs show similar properties to the local IRAS LIRGs. Most of the ISOCAM objects (>77%) are starburst galaxies, only ~23% are AGNs. Their 12+log(O/H) values are from 8.36 to 8.93 with a median value of 8.67, which is two times deficient than the local bright disks at the given M B. Models predict a total mass ranging from M  to  M , which can be twice of the stellar masses of distant LIRGs derived from the K band luminosities. Such massive disks could have formed ~50% of their metals and stellar masses since z~1. Cosmology model: H 0 = 70 km s -1 Mpc -1,  M = 0.3 and  = 0.7. References: Elbaz, D., Cesarsky, C. J. et al. 2002, A&A, 384, 848; Fadda, D. et al. 2002, A&A, 383, 838; Fioc, M. & Rocca-Volmerange, B. 1999, astro-ph/ (Pegase2); Kennicutt, R. C., Jr. 1992, ApJS, 79, 255; ApJ, 388, 310 (K92); Jansen, R. A. et al. 2000, ApJS, 126, 271; ApJS, 126, 331 (J20); Kobulnicky, H. A. et al. 2003, ApJ 599, 1006; Liang, Y. C. et al. 2004, A&A, 423, 867; Lilly, S. J. et al. 2003, ApJ 597, 730; Veilleux, S. et al. 1995, ApJS, 98, 171 (V95) Fig.1: The IR luminosity distribution of ISO-detected sample galaxies with z>0.4 in CFRS 3 h, UDSR and UDSF fields with the median value of log(L IR /L  )= This is similar to the local IRAS sample from V95 (the black dotted-line for BGSs; the red dashed- line for WGSs). Fig.2: Rest-frame spectrum of one sample galaxies, UDSR23. It is a LIRG with log(L IR /L  )= The emission and absorption lines are marked. The dashed boxes delimit the wavelength regions where strong sky lines are located. Fig.3: (a) The SFRs estimated from the extinction corrected Balmer lines compared with the SFR from infrared fluxes (  SFR/SFR~30%, Liang et al. 2004). (b) The relation between the extinction coefficients derived from the Balmer decrement (A V (Balmer)) and the energy balance between the IR radiation and the H  emission line luminosities (A V (IR)). The two dashed lines refer to the ±0.64 rms. The asterisks mark the upper limits. Fig.4: Diagnostic diagram. The solid line is from McCall et al.(1985) for theoretical sequence. The dashed line is from the photoionization model. Most of the ISOCAM galaxies (>77%) are starburst galaxies, and the AGN fraction is ~23%, which is consitent with Fadda et al. (2002) and Elbaz et al. (2002). Fig.5: Emission line flux ratios, compared with the local IRAS sample from V95 (the small squares). Most of the sample galaxies have relatively low ionization levels ([OIII]/H  <3). Fig.6: The M B -metallicity relations of the distant LIRGs (with the typical uncertainty of 0.08 dex on metallicity), compared with: (a) the local galaxies from K92 and J20; the vertical arrow shows the maximal extinction effect on M B, assuming an average extinction correction of A V =2.36; (b) Pegase2 infall models assuming a total mass of M  and infall times of 5 Gyr and 1 Gyr (the solid line and the dashed lines with pentagons) (Kobulnicky et al. 2003); (c) the galaxies with 0.4<z<0.82 from Kobulnicky et al. (2003); (d) the galaxies with 0.47<z<0.92 from Lilly et al. (2003), the solid triangles represent the LIRGs in their sample adopting constant extinction A V =1, which can be moved to lower metal abundances, reconciling to ours and those of Kobulnicky’sl values actually by considering the “own” A V of the galaxies. The solid, short-dashed and long-dashed are the linear least-squares fits for our distant LIRGs, the local sample, and the other two high-z samples, respectively. The international travel for this conference was funded by the Natural Science Foundation of China (NSFC) under No (Sample) (Diagnostics) (SFRs & Extinction) (Metallicities)