Diffuse Lya haloes around Lya emitters at z=3: do dark matter distributions determine the Lya spatial extents?

Using stacks of Lya images of 2128 Lya emitters (LAEs) and 24 proto-cluster UV-selected galaxies (LBGs) at z = 3.1, we examine the surface brightness profiles of Lya haloes around high-z galaxies as a function of environment and UV luminosity. We find that the slopes of the Lya radial profiles become flatter as the Mpc-scale LAE surface density increases, but that they are almost independent of the central UV luminosity. The characteristic exponential scalelength of the Lya haloes appears to be proportional to the square of the LAE surface density (r Ly a?S LAE 2). Including the diffuse, extended Lya haloes, the rest-frame Lya equivalent width of the LAEs in the densest regions approaches EW0 similar to 200 angstrom, the maximum value expected for young (<107?yr) galaxies. This suggests that Lya photons formed via shock compression by gas outflows or cooling radiation by gravitational gas inflows may partly contribute to the illumination of Lya haloes; however, most of their Lya luminosity can be explained by photoionization by or by scattering of Lya photons produced from H?ii regions in and around the central galaxies. Regardless of the source of Lya photons, if the Lya haloes trace the overall gaseous structure, following the dark matter distribution, it is not surprising that the Lya spatial extent depends more strongly on the surrounding Mpc-scale environment than on the activity of the central galaxies.