Large Scale Structures in COSMOS2020: Evolution of Star Formation Activity in Different Environments at 0.4 < z < 4

Abstract: To study the role of environment in galaxy evolution, we reconstruct the underlying density field of galaxies based on COSMOS2020 (The Farmer catalog) and provide the density catalog for a magnitude limited ($K_{s}<24.5$) sample of $\sim 210 \, k$ galaxies at $0.4<z\<5$ within the COSMOS field. The environmental densities are calculated using weighted Kernel Density Estimation (wKDE) approach with the choice of von Mises-Fisher kernel, an analog of the Gaussian kernel for periodic data. Additionally, we make corrections for the edge effect and masked regions in the field. We utilize physical properties extracted by LePhare to investigate the connection between star formation activity and the environmental density of galaxies in six mass-complete sub-samples at different cosmic epochs within $0.4<z\<4$. Our findings confirm a strong anti-correlation between star formation rate (SFR)/specific SFR (sSFR) and environmental density out to $z \sim 1.1$. At $1.1<z\<2$, there is no significant correlation between SFR/sSFR and density. At $2<z\<4$ we observe a reversal of the SFR/sSFR-density relation such that both SFR and sSFR increase by a factor of $\sim 10$ with increasing density contrast, $\delta$, from -0.4 to 5. This observed reversal at higher redshifts supports the scenario where an increased availability of gas supply, along with tidal interactions and a generally higher star formation efficiency in dense environments, could potentially enhance star formation activity in galaxies located in rich environments at $z\>2$.