3D distribution map of Hi gas and galaxies around an enormous Lyα nebula and three QSOs at z = 2.3 revealed by the Hi tomographic mapping technique

We present an IGM Hi tomographic map in a survey volume of 16 × 19 × 131 h⁻³comoving Mpc³ (cMpc³) centered at MAMMOTH-1 nebula and three neighbouring quasars at z = 2.3. MAMMOTH-1 nebula is an enormous Lyα nebula (ELAN), hosted by a type-II quasar dubbed MAMMOTH1-QSO, that extends over 1 h⁻¹ cMpc with not fully clear physical origin. Here we investigate the Hi-gas distribution around MAMMOTH1-QSO with the ELAN and three neighbouring type-I quasars, making the IGM Hi tomographic map with a spatial resolution of 2.6 h⁻¹ cMpc. Our Hi tomographic map is reconstructed with Hi Lyα forest absorption of bright background objects at z = 2.4 − 2.9: one eBOSS quasar and 16 Keck/LRIS galaxy spectra. We estimate the radial profile of Hi overdensity for MAMMOTH1-QSO, and find that MAMMOTH1-QSO resides in a volume with significantly weak Hi absorption. This suggests that MAMMOTH1-QSO has a proximity zone where quasar illuminates and photo-ionizes the surrounding Hi gas and suppresses Hi absorption, and that the ELAN is probably a photo-ionized cloud embedded in the cosmic web. The Hi radial profile of MAMMOTH1-QSO is very similar to those of three neighbouring type-I quasars at z = 2.3, which is compatible with the AGN unification model. We compare the distributions of the Hi absorption and star-forming galaxies in our survey volume, and identify a spatial offset between density peaks of star-forming galaxies and Hi gas. This segregation may suggest anisotropic UV background radiation created by star-forming galaxy density fluctuations.