2023ApJ...954..174L

The formation of the first supermassive black holes is expected to have occurred in some most pronounced matter and galaxy overdensities in the early universe. We have conducted a submillimeter wavelength continuum survey of 54 z ∼ 6 quasars using the Submillimeter Common-User Bolometre Array-2 on the James Clerk Maxwell Telescope to study the environments around z ∼ 6 quasars. We identified 170 submillimeter galaxies (SMGs) with above 3.5σ detections in 450 or 850 μm maps. Their far-IR luminosities are (2.2-6.4) × 10¹²L_⊙, and their star formation rates are ∼400-1200 M_⊙ yr^–1. We also calculated the SMGs' differential and cumulative number counts in a combined area of ∼620 arcmin². To a 4σ detection (at ∼5.5 mJy), SMGs' overdensity is ${0.68}_{-0.19}^{+0.21}$ (±0.19), exceeding the blank-field source counts by a factor of 1.68. We find that 13/54 quasars show overdensities (at ∼5.5 mJy) of δ_SMG ∼ 1.5-5.4. The combined area of these 13 quasars exceeds the blank-field counts with the overdensity to 5.5 mJy of δ_SMG ∼ ${2.46}_{-0.55}^{+0.64}$ (±0.25) in the regions of ∼150 arcmin². However, the excess is insignificant on the bright end (e.g., 7.5 mJy). We also compare results with previous environmental studies of Lyα emitters and Lyman break galaxies on a similar scale. Our survey presents the first systematic study of the environment of quasars at z ∼ 6. The newly discovered SMGs provide essential candidates for follow-up spectroscopic observations to test whether they reside in the same large-scale structures as the quasars and search for protoclusters at an early epoch.