Astrophysicists in ASPIRE use telescopes across the electromagnetic spectrum to study the origin of the universe, its structure, and its evolution over cosmic time. This includes investigations of how the first stars and galaxies in the universe formed and evolved, measuring the large scale structure of the universe, and studying how galaxy properties are tied to large scale structure and dark matter.
It has long been known that there is a tight correlation between galaxy morphology and local environment (Dressler 1980). Elliptical galaxies tend to reside in the densest environments while spiral galaxies dominate in the field. Since a galaxy’s morphology is also correlated with its SFR, the densest environments are dominated by passive systems while galaxies actively forming stars reside in less dense environments, like group and field environments. These relations, the morphology-density relation, and the SFR-density relation have been observed by a plethora of studies in the local universe. In recent years investigations have pushed outward to see how these relations have evolved over cosmic time, but so far, these studies have found conflicting results and the picture at high redshift remains unclear. Some authors have argued that at z > 1, when today’s elliptical galaxies were forming the bulk of their stars, the SFR-density relation should be reversed compared to the local relation. While some groups find evidence for this, others find no reversal at all or a flatting of the relationship at higher redshift. Our group is using the plethora of photometric and spectroscopic redshifts available in the COSMOS and CANDELS deep fields to construct environmental density maps and quantify how galaxy environment impacts star formation, AGN activity, and morphology out to z~3.