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

We present the median surface brightness profiles of diffuse Ly alpha haloes (LAHs) around star-forming galaxies by stacking 155 spectroscopically confirmed Ly alpha emitters (LAEs) at 3 < z < 4 in the MUSE Extremely Deep Field (MXDF) with a median Ly alpha luminosity of L-Ly alpha approximate to 10(41.1) erg s(-1). After correcting for a systematic surface brightness offset we identified in the data cube, we detect extended Ly alpha emission out to a distance of approximate to 270 kpc. The median Ly alpha 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 Ly alpha 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 Ly alpha surface brightness is dominated by the LAHs of nearby LAEs. We find no clear evidence of redshift evolution of the observed Ly alpha 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.