SILVERRUSH. IX. Lya Intensity Mapping with Star-Forming Galaxies at z=5.7 and 6.6: A Possible Detection of Extended Lya Emission at $\gtrsim$100 comoving kpc around and beyond the Virial-Radius Scale of Galaxy Dark Matter Halos

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We present results of the cross-correlation Ly$\alpha$ intensity mapping with Subaru/Hyper Suprime-Cam (HSC) ultra-deep narrowband images and Ly$\alpha$ emitters (LAEs) at $z=5.7$ and $6.6$ in a total area of $4$ deg$^2$.

• Although overwhelming amount of data quality controls have been performed for the narrowband images, we further conduct extensive analysis evaluating systematics of large-scale point-spread-function wings, sky subtractions, and unknown errors based on physically uncorrelated signals and sources found in real HSC images and object catalogs, respectively.
• Removing the systematics, we carefully calculate cross-correlations between Ly$\alpha$ intensity of the narrowband images and the LAEs.
• We tentatively identify very diffuse Ly$\alpha$ emission with the $\simeq 3\sigma$ ($\simeq 2\sigma$) significance at $\gtrsim$ 100 comoving kpc (ckpc) far from the LAEs at $z=5.7$ ($6.6$), around and probably even beyond a virial radius of star-forming galaxies with $M_\mathrm{h}\sim10^{11}M_\odot$.