Investigation of metallicity gradient of the thick disc in the galaxy

PhD thesis study is aimed to test the Galactic chemical formation and evolution by developing new metallicity and absolute magnitude calibrations in SDSS photometric system and applying these new calibrations on a star field at middle/high Galactic latitudes on the northern Galactic hemisphere. To do so, 168 F and G spectral type main-sequence stars with accurate photometric, spectroscopic and astrometric data were used in ultra-violet excess method in order to developed metallicity and absolute magnitude calibrations. Then, these calibrations were used on 1,437,467 F and G spectral type main-sequence stars, which their metallicity range -2 < [Fe/H] < 0.3 dex, that reside on northern Galactic hemisphere at b > 50 degree of SDSS DR12 to calculate metallicity gradients radial from Galactic center and vertically from the Galactic plane. Average calculated radial metallicity gradient for thin disc, which is effective on 0.5 < Z <1.74 kpc is d[Fe/H]/dR = -0.042(0.011) dex/kpc, while this values are closer the zero thick disc and halo. In vertical metallicity gradient calculations from the Galactic plane 6 < R < 10, 10 < R < 15, and 15 < R < 20 kpc radial distance intervals were considered. For the thin disc population which is prominent at 6 < R < 10 kpc distance interval vertical metallicity gradient is d[Fe/H]/dZ = -0.308(0.015) dex/kpc and for thick disk in the same interval vertical metallicity gradient is d[Fe/H]/dZ = -0.164(0.011) dex/kpc. In 10 < R < 15 kpc distance interval vertical metallicity gradient for the thick disc and halo are d[Fe/H]/dZ = -0.172(0.01)2 and d[Fe/H]/dZ = -0.007(0.001) dex/kpc, respectively. In 15< R < 20 kpc distance interval vertical metallicity gradient give values closer to zero. In thesis study, the observational metallicity gradients values both for radial and vertical directions from Galactic centre and Galactic plane, respectively, are compared with the synthetic results of Galaxia model which uses the star count methods. Both calculations that were performed for observed and synthetic values are coherent with the metallicity gradient results that were obtained directly from observational data in this study. Finally, the thin disc radial metallicity gradient supports the inside out formation scenario, while thick disc and halo have no radial metallicity gradient, which suggests that these components have not been through the similar formation process. On the other hand, the metallicity gradients perpendicular to the Galactic plane calculated for all three Galactic components give support to the monolithic collapse scenario of the Galactic formation.