SILVERRUSH. IX. Lyα Intensity Mapping with Star-forming Galaxies at z=5.7 and 6.6: A Possible Detection of Extended Lyα Emission at ≳100 Comoving Kiloparsecs around and beyond the Virial-radius Scale of Galaxy Dark Matter Halos

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 an overwhelming amount of data quality controls have been performed for the narrowband images, we further conduct extensive analyses 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 similar or equal to 3 sigma (similar or equal to 2 sigma) significance at greater than or similar to 100 comoving kiloparsecs (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 (h) similar to 10(11) M (circle dot). The diffuse Ly alpha emission possibly extends up to 1000 ckpc with the surface brightness of 10(-20)-10(-19) erg s(-1) cm(-2) arcsec(-2). We confirm that the small-scale (<150 ckpc) Ly alpha radial profiles of LAEs are consistent with those obtained by recent Multi-Unit Spectroscopic Explorer observations. Comparisons with numerical simulations suggest that the large-scale (similar to 150-1000 ckpc) Ly alpha emission are not explained by unresolved faint neighboring galaxies including satellites, but by a combination of Ly alpha photons emitted from the central LAE and other unknown sources, such as cold-gas streams and galactic outflow. We find no evolution in the Ly alpha radial profiles of our LAEs from z = 5.7 to 6.6, where theoretical models predict a flattening of the profile slope made by cosmic reionization, albeit with our moderately large observational errors.

Automated summary

Results of 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 show the presence of potential Ly alpha emission from physically uncorrelated signals and sources.