SCUBA-2 High Redshift Bright Quasar Survey. II. The Environment of z ∼ 6 Quasars at Submillimeter Band

Abstract

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 3.5 σ detections in 450 or 850 μ m maps. Their far-IR luminosities are (2.2–6.4) × 10 ^12 L _⊙ , 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 arcmin ^2 . To a 4 σ 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 arcmin ^2 . However, the excess is insignificant on the bright end (e.g., 7.5 mJy). We also compare results with previous environmental studies of Ly α 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.

Keywords

• Quasars
• Submillimeter astronomy
• Active galaxies