JCMT/SCUBA-2 uncovers an excess of 850 μm counts on megaparsec scales around high-redshift quasars. Characterization of the overdensities and their alignment with the quasars' Lyα nebulae

We conducted a systematic survey of the environment of high-redshift quasars at submillimeter wavelengths to unveil and characterize the surrounding distribution of dusty submillimeter galaxies (SMGs). We took sensitive observations with the SCUBA-2 instrument on the James Clerk Maxwell Telescope for 3 enormous Lyman-alpha nebulae (ELANe) and 17 quasar fields in the redshift range 2 < z < 4.2 selected from recent Lyman alpha (Lyα) surveys. These observations uncovered 523 and 101 sources at 850 μm and 450 μm, respectively, with signal-to-noise ratios (S/N) > 4 or detected in both bands at S/N > 3. We ran self-consistent Monte Carlo simulations to construct 850 μm number counts and unveil an excess of sources in 75% of the targeted fields. Overall, regions around ELANe and quasars are overabundant with respect to blank fields by a factor of 3.4 ± 0.4 and 2.5 ± 0.2, respectively (weighted averages). Therefore, the excess of submillimeter sources is likely part of the megaparsec-scale environment around these systems. By combining all fields and repeating the count analysis in radial apertures, we find (at high significance, ≳5σ) a decrease in the overdensity factor from > 3 within ∼2 cMpc to ∼2 in the annulus at the edge of the surveyed field (∼10 cMpc), which suggests that the physical extent of the overdensities is larger than our maps. We computed preferred directions for the overdensities of SMGs from the positions of the sources and used them to orient and create stacked maps of source densities for the quasars' environment. This stacking unveils an elongated structure reminiscent of a large-scale filament with a scale width of ≈3 cMpc. Finally, the directions of the overdensities are roughly aligned with the major axis of the Lyα nebulae, suggesting that the latter trace, on scales of hundreds of kiloparsecs, the central regions of the projected large-scale structure described by the SMGs on megaparsec scales. Confirming member associations of the SMGs is required to further characterize their spatial and kinematic distribution around ELANe and quasars.

Tables F.1 to F.40 (the source catalogs) and a copy of the reduced images are available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/676/A51