2024ApJ...974..275E

We expect luminous (M₁₄₅₀ ≲ -26.5) high-redshift quasars to trace the highest-density peaks in the early Universe. Here, we present observations of four z ≳ 6 quasar fields using JWST/NIRCam in the imaging and wide-field slitless spectroscopy mode and report a wide range in the number of detected [O III]-emitting galaxies in the quasars' environments, ranging between a density enhancement of δ ≈ 65 within a 2 cMpc radius-one of the largest protoclusters during the Epoch of Reionization discovered to date-to a density contrast consistent with zero, indicating the presence of a UV-luminous quasar in a region comparable to the average density of the Universe. By measuring the two-point cross-correlation function of quasars and their surrounding galaxies, as well as the galaxy autocorrelation function, we infer a correlation length of quasars at 〈z〉 = 6.25 of ${r}_{0}^{\mathrm{QQ}}={22.0}_{-2.9}^{+3.0}\,\mathrm{cMpc}\,{h}^{-1}$, while we obtain a correlation length of the [O III]-emitting galaxies of ${r}_{0}^{\mathrm{GG}}=4.1\,\pm 0.3\,\mathrm{cMpc}\,{h}^{-1}$. By comparing the correlation functions to dark-matter-only simulations we estimate the minimum mass of the quasars' host dark matter halos to be ${\mathrm{log}}_{10}({M}_{\mathrm{halo},\min }/{M}_{\odot })={12.43}_{-0.15}^{+0.13}$ (and ${\mathrm{log}}_{10}({M}_{\mathrm{halo},\min }^{[\mathrm{OIII}]}/{M}_{\odot })\,={10.56}_{-0.03}^{+0.05}$ for the [O III] emitters), indicating that (a) luminous quasars do not necessarily reside within the most overdense regions in the early Universe, and that (b) the UV-luminous duty cycle of quasar activity at these redshifts is f_duty ≪ 1. Such short quasar activity timescales challenge our understanding of early supermassive black hole growth and provide evidence for highly dust-obscured growth phases or episodic, radiatively inefficient accretion rates.