BEACON: JWST NIRCam Pure-parallel Imaging Survey. IV. A Systematic Search for Galaxy Overdensities and Evidence for Gas Accretion Mode Transition

TL;DR

This study uses JWST NIRCam data to identify galaxy overdensities across redshifts 1.5 to 5, revealing how galaxy quenching correlates with environment and halo mass, indicating a transition in gas accretion modes over cosmic time.

Contribution

It introduces a systematic method to detect galaxy overdensities using photometric redshift PDFs and analyzes their properties, providing new insights into galaxy quenching mechanisms and environmental effects.

Findings

Overdensities are identified at $1.5<z<5$ with >4σ significance.

Quenched fractions increase with halo mass and local density, especially at $z<2$.

Evidence suggests a transition in gas accretion modes around $z oughly 2-3$.

Abstract

We systematically search for galaxy overdensities using 20 independent fields with a minimum of six filters (F090W, F115W, F150W, F277W, F356W, and F444W) from BEACON, the JWST Cycle 2 NIRCam pure-parallel imaging survey. We apply an adaptive kernel-density estimation method that incorporates the full photometric redshift probability distribution function of each galaxy to map galaxy overdensities, and identify 207 significant ($>4\,\sigma$) overdensities at $1.5<z<5$. We measure the quenched-galaxy fraction, the median specific star formation rate (sSFR), the total halo mass, and the local galaxy density of each system. By investigating the correlation among these observables, we find that galaxy quenching proceeds in two paths:($i$) Overdensities within more massive halos exhibit higher quenched fractions and lower averaged sSFRs. This trend weakens at $z\gtrsim2$, consistent with cold gas streams penetrating shock-heated massive halos and sustaining star formation activity at early times. ($ii$) We also find a dependence of the same parameters on local densities at $z<2$, where the quenched fraction increases and the sSFR decreases toward higher densities. The environmental trend in sSFR weakens at $z\sim2$--$3$ and shows tentative evidence for a reversal at $z>3$, potentially due to a larger cold gas supply in earlier times. Our study reveals a complex interplay between individual galaxies and large-scale environmental properties, marking the onset of environmental effects on galaxy quenching in massive halos at cosmic noon.