Insights into Galaxy Morphology and Star Formation: Unveiling Filamentary Structures around an Extreme Overdensity at z ∼ 1.5 Traced by [OII] Emitters

We explore the morphological features and star formation activities of [OII] emitters in the COSMOS UltraDeep field at z ∼ 1.5 using JWST NIRCam data from the COSMOS-Web survey and Subaru Hyper Suprime-Cam. We also report the discovery of large filamentary structures traced by [OII] emitters, surrounding an extremely overdense core with a galaxy number density ∼11× higher than the field average. These structures span over 50 cMpc, underscoring their large scale in the cosmic web at this epoch. After matching the stellar mass distributions, the core galaxies show a higher frequency of disturbances (50% ± 9%) than those in outskirts (41% ± 9%) and the field (21% ± 5%), indicative of more frequent mergers and interactions in the innermost ≲1.5 arcmin region. Additionally, we observe that specific star formation rates are elevated in denser environments. A Kolmogorov-Smirnov (KS) test comparing the distribution of specific star formation rates of core and field galaxies yields a p-value of 0.02, suggesting an enhancement of star-formation activity driven by the dense environment. Our findings underscore the environmental impact on galaxy evolution during a pivotal cosmic epoch and set the stage for further investigation with the increasing larger data from upcoming surveys.