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ABSTRACT Recent observations from the EIGER JWST program have measured for the first time the quasar–galaxy cross-correlation function at $$z\approx 6$$. The autocorrelation function of faint $$z\approx 6$$ quasars was also recently estimated. These measurements provide key insights into the properties of quasars and galaxies at high redshift and their relation with the host dark matter haloes. In this work, we interpret these data building upon an empirical quasar population model that has been applied successfully to quasar clustering and demographic measurements at $$z\approx 2\!-\!4$$. We use a new, large-volume N-body simulation with more than a trillion particles, FLAMINGO-10k, to model quasars and galaxies simultaneously. We successfully reproduce observations of $$z\approx 6$$ quasars and galaxies (i.e. their clustering properties and luminosity functions), and infer key quantities such as their luminosity–halo mass relation, the mass function of their host haloes, and their duty cycle/occupation fraction. Our key findings are (i) quasars reside on average in $$\approx 10^{12.5}\, {\rm M}_{\odot }$$ haloes (corresponding to $$\approx 5\sigma$$ fluctuations in the initial conditions of the linear density field), but the distribution of host halo masses is quite broad; (ii) the duty cycle of (UV-bright) quasar activity is relatively low ($$\approx 1~{{\ \rm per\ cent}}$$); (iii) galaxies (that are bright in [O iii]) live in much smaller haloes ($$\approx 10^{10.9}\, {\rm M}_{\odot }$$) and have a larger duty cycle (occupation fraction) of $$\approx 13~{{\ \rm per\ cent}}$$. Finally, we focus on the inferred properties of quasars and present a homogeneous analysis of their evolution with redshift. The picture that emerges reveals a strong evolution of the host halo mass and duty cycle of quasars at $$z\approx 2\!-\!6$$, and calls for new investigations of the role of quasar activity across cosmic time. 

ABSTRACT Motivated by spectroscopic confirmation of three overdense regions in the COSMOS field at z ∼ 3.35, we analyse the uniquely deep multiwavelength photometry and extensive spectroscopy available in the field to identify any further related structure. We construct a three-dimensional density map using the Voronoi tesselation Monte Carlo method and find additional regions of significant overdensity. Here, we present and examine a set of six overdense structures at 3.20 < z < 3.45 in the COSMOS field, the most well-characterized of which, PCl J0959 + 0235, has 80 spectroscopically confirmed members and an estimated mass of 1.35 × 1015 M⊙, and is modelled to virialize at z ∼ 1.5−2.0. These structures contain 10 overdense peaks with >5σ overdensity separated by up to 70 cMpc, suggestive of a proto-supercluster similar to the Hyperion system at z ∼ 2.45. Upcoming photometric surveys with JWST such as COSMOS-Web, and further spectroscopic follow-up will enable more extensive analysis of the evolutionary effects that such an environment may have on its component galaxies at these early times. 

ABSTRACT Simulations predict that the galaxy populations inhabiting protoclusters may contribute considerably to the total amount of stellar mass growth of galaxies in the early universe. In this study, we test these predictions observationally, using the Taralay protocluster (formerly PCl J1001+0220) at z ∼ 4.57 in the COSMOS field. With the Charting Cluster Construction with VUDS and ORELSE (C3VO) survey, we spectroscopically confirmed 44 galaxies within the adopted redshift range of the protocluster (4.48 < z < 4.64) and incorporate an additional 18 galaxies from ancillary spectroscopic surveys. Using a density mapping technique, we estimate the total mass of Taralay to be ∼1.7 × 1015 M⊙, sufficient to form a massive cluster by the present day. By comparing the star formation rate density (SFRD) within the protocluster (SFRDpc) to that of the coeval field (SFRDfield), we find that SFRDpc surpasses the SFRDfield by Δlog (SFRD/M⊙yr−1 Mpc−3) = 1.08 ± 0.32 (or ∼12 ×). The observed contribution fraction of protoclusters to the cosmic SFRD adopting Taralay as a proxy for typical protoclusters is $$33.5~{{\ \rm per\ cent}}^{+8.0~{{\ \rm per\ cent}}}_{-4.3~{{\ \rm per\ cent}}}$$, a value ∼2σ higher than the predictions from simulations. Taralay contains three peaks that are 5σ above the average density at these redshifts. Their SFRD is ∼0.5 dex higher than the value derived for the overall protocluster. We show that 68 per cent of all star formation in the protocluster takes place within these peaks, and that the innermost regions of the peaks encase $$\sim 50~{{\ \rm per\ cent}}$$ of the total star formation in the protocluster. This study strongly suggests that protoclusters drive stellar mass growth in the early universe and that this growth may proceed in an inside-out manner.