An analysis of the internal conditions of galaxies at z≈0.1 and the identifying features of galaxy sub-types

We have utilised the eighth data release of the Sloan Digital Sky Survey (SDSS), in combination with cloudy photo-ionisation models, to investigate the physical condi- tions of local galaxies at z ≈ 0.1. This was done by separating our selected data into active and passive galaxies, and identifying star-forming, starburst and active galactic nucleus (AGN) sources. We found that stellar mass is a key predictor of galaxy type: most (80%) low mass galaxies are starburst galaxies, while the most massive galaxies are passive, with these being ≈ 100% of the population at z ∼ 0.1 for stellar masses in excess of 1011.8 M⊙. We find that AGN are overall rare, but they become fractionally more important at higher stellar masses. cloudy photo-ionisation models reveal that star-forming galaxies have a strong linear relationship between temperature, metallic- ity and stellar mass, recovering the well studied mass-metallicity relation in the local Universe. AGN in SDSS are relatively metal rich at all stellar masses and we find that they are found at density peaks within the cosmic web. Overall, our results reveal a picture in which the most metal poor, lower mass galaxies are still actively assembling their stellar mass, while the most massive sources have assembled the bulk of their mass at higher redshift