Median surface-brightness profiles of Lyman-α haloes in the MUSE Extremely Deep Field

We present the median surface brightness profiles of diffuse Lyα haloes (LAHs) around star-forming galaxies by stacking 155 spectroscopically confirmed Lyα emitters (LAEs) at 3 < z < 4 in the MUSE Extremely Deep Field (MXDF) with a median Lyα luminosity of L_Lyα ≈ 10^41.1 erg s⁻¹. After correcting for a systematic surface brightness offset we identified in the data cube, we detect extended Lyα emission out to a distance of ≈270 kpc. The median Lyα surface-brightness profile shows a power-law decrease in the inner 20 kpc and a possible flattening trend at a greater distance. This shape is similar for LAEs with different Lyα luminosities, but the normalisation of the surface-brightness profile increases with luminosity. At distances over 50 kpc, we observe a strong overlap of adjacent LAHs, and the Lyα surface brightness is dominated by the LAHs of nearby LAEs. We find no clear evidence of redshift evolution of the observed Lyα profiles when comparing with samples at 4 < z < 5 and 5 < z < 6. Our results are consistent with a scenario in which the inner 20 kpc of the LAH is powered by star formation in the central galaxy, while the LAH beyond a radius of 50 kpc is dominated by photons from surrounding galaxies.