3D Distribution Map of HI Gas and Galaxies Around an Enormous Ly$\alpha$ Nebula and Three QSOs at $z=2.3$ Revealed by the HI Tomographic Mapping Technique

28 Apr 2020  ·  Mukae Shiro, Ouchi Masami, Cai Zheng, Lee Khee-Gan, Prochaska J. Xavier, Cantalupo Sebastiano, Zheng Zheng, Nagamine Kentaro, Suzuki Nao, Silverman John D., Misawa Toru, Inoue Akio K., Hennawi Joseph F., Matsuda Yuichi, Mawatari Ken, Sugahara Yuma, Kojima Takashi, Ono Yoshiaki, Shibuya Takatoshi, Harikane Yuichi, Fujimoto Seiji, Chiang Yi-Kuan, Zhang Haibin, Kakuma Ryota ·

We present an IGM HI tomography map in a survey volume of $16 \times 19 \times 131 \ h^{-3} {\rm comoving \ Mpc}^{3}$ (cMpc$^3$) centered at MAMMOTH-1 nebula and three neighbouring quasars at $z=2.3$. MAMMOTH-1 nebula is an enormous Ly$\alpha$ 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 tomography map with a spatial resolution of $2.6\ h^{-1}$ cMpc. Our HI tomography map is reconstructed with HI Ly$\alpha$ 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 flux 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.

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Astrophysics of Galaxies