The Effect of Environment on the Properties of the Most Massive Galaxies at 0.5 < z < 2.5 in the COSMOS-DASH Field

How the environment influences the most massive galaxies is still unclear. To explore the effects of the environment on morphology and star formation in the most massive galaxies at high redshift, we select galaxies with stellar mass log(M?/M & ODOT;)>11 z < 2.5 in the COSMOS-DASH field, which is the largest field with near-infrared photometric observations using HST/WFC3 to date. Combining these with the newly published COSMOS2020 catalog, we estimate the localized galaxy overdensity using a density estimator within the Bayesian probability framework. With the overdensity map, no significant environmental dependence is found in the distributions of Sersic index and effective radius. When we consider the star formation state, galaxies at a lower density are found to have a higher median specific star formation rate (sSFR) at 0.5 < z < 1.5. But for star-forming galaxies only, sSFR is independent of the environment over the whole redshift range, indicating that the primary effect of the environment might be to control the quiescent fraction. Based on these observations, the possible environmental quenching process for these massive galaxies might be mergers.