2021ApJ...907....3L

The correlation between neutral hydrogen (H I) in the intergalactic medium (IGM) and galaxies attracts great interest. We select four fields that include several coherently strong Lyα absorption systems at z ∼ 2.2 detected using background quasars from the whole SDSS/(e) Baryon Oscillation Spectroscopic Survey (BOSS) database. Deep narrowband and g-band imaging are performed using the Hyper Suprime-Cam on the Subaru Telescope. We select 2642 Lyα emitter (LAE) candidates at z = 2.177 ± 0.023 down to the Lyα luminosity of L_Lyα ≃ 2 x 10⁴² erg s^–1 to construct the galaxy overdensity maps, covering an effective area of 5.39 deg². Combining the sample with the Lyα absorption estimated from 64 (e) BOSS quasar spectra, we find a moderate to strong correlation between the LAE overdensity δ_LAE and the effective optical depth τ_LoS in lines of sight, with P value = 0.09% or <0.01% when the field containing a significant quasar overdensity is included or excluded. Cross-correlation analysis also clearly suggests that up to 4 ± 1 pMpc, LAEs tend to cluster in regions rich in H I gas, as indicated by the high τ_LoS, and avoid the low τ_LoS regions where the H I gas is deficient. By averaging the τ_LoS as a function of the projected distance (d) to LAEs, we find a 30% excess signal at 2σ level at d < 200 pkpc, indicating the dense H I in the circumgalactic medium, and a tentative excess at 400 < d < 600 pkpc in the IGM regime, corroborating the cross-correlation signal detected at about 0.5 pMpc. These statistical analyses suggest that galaxy-IGM H I correlations exist on scales ranging from several hundred pkpc to several pMpc at z ∼ 2.2.