The formation and evolution of galaxies are driven by their interaction with the Circumgalactic Medium (CGM). The recent discovery of the Enormous Lyα Nebulae (ELANe), with sizes of a few hundred kpc, provides the opportunity to constrain the emission of the CGM properties directly. However, with the exception of a few ELANe around bright quasars, the Lyα emission mechanism of several ELANe is still uncertain, hampering the possibility of constraining gas properties such as density and kinematics. In order to overcome this limitation, we propose to detect Hα emission from one of the largest ELANe discovered so far at z=2.3 not associated with a bright quasar, using MOIRCS narrow-band imaging. Due to the non-resonant nature, the Hα line can be a better alternative to the Lyα for inferring the gas properties. Together with archived observation of multiple highly extended emissions such as the HeII and CIV on ≥ 150 kpc, we can perform the spatially resolved line ratio diagnostics up to the edge of the halo for the first time. From the inferred gas properties such as gas density, metallicity, and kinematics, we can reveal the co-evolution of the galaxy and the gas environment in great detail on an unprecedentedly large physical scale.
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