Diffuse Ly α haloes around Ly α emitters at z = 3 ⋆ : Do dark matter distributions determine the Ly α spatial extents ?

Using stacks of Lyα images of 2128 Lyα emitters (LAEs) and 24 protocluster UVselected galaxies (LBGs) at z = 3.1, we examine the surface brightness profiles of Lyα haloes around high-z galaxies as a function of environment and UV luminosity. We find that the slopes of the Lyα radial profiles become flatter as the Mpc-scale LAE surface densities increase, but they are almost independent of the central UV luminosities. The characteristic exponential scale lengths of the Lyα haloes appear to be proportional to the square of the LAE surface densities (rLyα ∝ Σ 2 LAE). Including the diffuse, extended Lyα haloes, the rest-frame Lyα equivalent width of the LAEs in the densest regions approaches EW0 ∼ 200 Å, the maximum value expected for young (< 10 7 yr) galaxies. This suggests that Lyα photons formed via shock compression by gas outflows or cooling radiation by gravitational gas inflows may partly contribute to illuminate the Lyα haloes; however, most of their Lyα luminosity can be explained by photoionisation by ionising photons or scattering of Lyα photons produced in H ii regions in and around the central galaxies. Regardless of the source of Lyα photons, if the Lyα haloes trace the overall gaseous structure following the dark matter distributions, it is not surprising that the Lyα spatial extents depend more strongly on the surrounding Mpc-scale environment than on the activities of the central galaxies.