Star formation efficiency of galaxies across large-scale galactic environments

The effect of a galaxy's large-scale environment on its evolution and properties, including the star formation activity, has been a matter of debate for decades. Observations of several distant protoclusters show that their member galaxies were mostly starburst and blue in the early universe. On the contrary, cluster galaxies at z<1 are mainly quenched and red. Does this trend arise from observational biases, or is it a consequence of the large-scale environment? To answer these questions, I will present new results from an investigation of the relationship between the star formation activity of galaxies and their environment in a large galaxy sample from the Simba cosmological simulation. We analyze the relations between the cold gas, the star formation activity, and the environment overdensity of galaxies, and how these relations vary with redshift. Our work shows that the environmental overdensity has a subtle but discernable effect on the star formation activity of galaxies. These effects are most prominent in lower-mass galaxies at 0<z<1. Among these galaxies, those in low-density regions form stars more efficiently than those in denser regions of the universe. Our work provides a theoretical framework to interpret the seemingly contradictory observational results, as well as predictions for what we can expect for upcoming wide-field galaxy surveys.