Star Formation Properties Of Poor Metal Galaxies

In recent years, a large number of massive emission-line galaxies at low redshift has been obtained by large spectral surveys. The follow-up analysis of large spectroscopic samples shows that there exist some tight connections among stellar mass, metallicity and star formation rate, such as the relation between stellar mass and star formation rate (SFR) (i.e. main sequence relation), mass -metallicity relation (MZR), and fundamental metallicity relation (FMR), which provides important observational constraints for understanding the processes of star formation within galaxies. Do these relations still hold for the galaxies with lower masses at poorer metallicities and higher redshifts ? This is a key question for understanding the formation and evolution of galaxies.In this thesis we use the database (v5.10.0) of the SDSS-IV eBOSS spectro-scopic survey, and select 44 star-forming galaxies (SFGs) at 0.6 < z < 0.9 for the detection of weak emission line [OIII]λ4363. The gas-phase metallicities of these galaxies can be directly determined by the Te method, and the stellar masses and star formation rates can be quantitatively estimated. Main results are as follows:(1) Our [OIII]λ4363 sample contains only metal-poor galaxies, and the mean metallicity of the sample is 12 + log(O/H) = 7.9, corresponding to 1/6 Z☉. The sample contains 9 extremely metal-poor galaxies with metallicities less than 1/10 Z☉.The metallicity for the most metal-poor SFG is 7.25 ± 0.09, about 1/25 Z☉o.(2) Compared with the z～1 SFGs with normal metallicities,the metal-poor SFGs in our sample are found to have more intense star formation activities.Relative to the local MZR (Andrews & Martini 2013, hereafter AM13)[4] , our metal-poor SFG sample at 0.6<z<0.9 distributes below the local MZR in AM13 with a overall 2σ deviation. Taking the DEEP2 and SDF [OIII]λ4363 samples into account, the MZR at higher redshifts evolves toward the lower metallicity.(3) Our sample is divided into two subsamples according to their specific star formation rates (sSFRs). It is found that the metallicities for the low-sSFR subsample are poorer. Relative to the local MZR, the offset in metallicity for these two subsamples are completely different. The metallicity offsets against the local MZR in AM13 for low-sSFR subsample appear a larger deviation toward the lower metallicity, while the high-sSFR subsample tends to have higher gas-phase metallicities.(4) Similar to the DEEP2, SDF [OIII]λ4363 samples, the high-sSFR sub-sample can be well fitted by the local FMR in AM13 with an average deviation of -0.11 ± 0.24 dex. Universality of the FMR at 0.6 < z < 0.9 is verified. Addi-tionally, there is a certain degree of deviation from the local FMR for low-sSFR subsample.