Large-Scale Structure in COSMOS-Web: Tracing Galaxy Evolution in the Cosmic Web up to $z \sim 7$ with the Largest JWST Survey

Abstract

We present a reconstruction of the large-scale structure using the James Webb Space Telescope's (JWST) COSMOS-Web program to trace environmentally driven galaxy evolution up to $z\sim7$. We applied a weighted kernel density estimation method to 160,000 galaxies with robust photometric redshifts. We find that stellar mass has a positive correlation with density at all redshifts, stronger for quiescent galaxies (QGs) at $z\lesssim2.5$, while at higher redshifts ($2.5\lesssim z\lesssim5.5$) this trend is confined to extreme overdense environments, consistent with early mass assembly in proto-clusters. The star-formation rate (SFR) shows a negative trend with density for QGs at $z\lesssim1.2$, reversing at $z\gtrsim1.8$, while star-forming galaxies (SFGs) show a mild positive correlation up to $z\sim5.5$. The specific SFR remains nearly flat for SFGs and declines with density for QGs at $z\lesssim1.2$. Moreover, mass and environmental quenching efficiencies show that mass-driven processes dominate at $z\gtrsim2.5$, the two processes act with comparable strength between $0.8\lesssim z\lesssim2.5$, and environmental quenching becomes stronger for low-mass galaxies ($M_\star\lesssim10^{10} M_\odot$) at $z\lesssim0.8$. These findings reveal that large-scale structure drives galaxy evolution by enhancing early mass assembly in dense regions and increasingly suppressing star formation in low-mass systems at later times, establishing the environmental role of the cosmic web across cosmic history. COSMOS-Web, the largest JWST survey, provides accurate and deep photometric redshifts, reaching 80% mass completeness at $\log(M_\star/M_\odot)\sim8.7$ at $z\sim7$, enabling the first view of how environments shaped galaxy evolution from the epoch of reionization to the present day.

Figures (17)

• Figure 1: Galaxy stellar mass as a function of redshift. The red curve shows the stellar-mass completeness limit derived following the method of Pozzetti2010, obtained by rescaling stellar masses to the total F444W magnitude limit of the survey ($27.5$) and taking the 90th percentile of the resulting distribution in each redshift bin. The solid red line represents the best-fit polynomial in $(1 + z)$. The black line marks the stellar mass threshold of $\log(M_\star/M_\odot) = 8$ used in our sample selection.
• Figure 2: Count of COSMOS-Web sources after all selection cuts. Red dashed circles show HSC-masked regions. Top: Masked regions excluded. Bottom: Masked regions included. Keeping detections inside the masks still leaves low number density inside the red circles, which would bias our LSS analysis.
• Figure 3: Top: Redshift distribution of galaxies in the COSMOS-Web sample. Each bin corresponds to a redshift slice used in the density field reconstruction. Bottom: Normalized photometric redshift uncertainty, $\sigma_z / (1 + z)$, as a function of redshift. The color map shows the number of galaxies at each redshift–uncertainty bin on a logarithmic scale. The red dashed line shows the median uncertainty in each redshift slice.
• Figure 4: Steps in the construction of the density field for a redshift slice at $z \sim 3.7$. Top left: distribution of galaxies and artificial sources colored by their weight. Top right: adaptive bandwidth assigned to each galaxy. Bottom left: boundary correction factor $\eta$ applied near survey edges. Bottom right: final density field $1+\delta$. Circles show the HSC masked regions.
• Figure 5: Evolution of overdensity maps in the COSMOS-Web field across cosmic time. Each panel shows the overdensity field for a fixed comoving slice; color bars are scaled independently in each redshift bin. While absolute overdensity amplitudes cannot be directly compared across panels, the maps illustrate the changing topology and distribution of LSS with increasing redshift. Circles mark the HSC star-masked regions.