Evolution of the composite Lyα line profile (red line) as a function of the expansion velocity of halo 1 (V_exp1) and of halo 2 (V_exp2). The blue line shows the observed Lyα line of Mrk 1486 through the COS aperture, the gray line shows the line emerging from halo 1, and the clear blue line shows the one escaping from halo 2. In the four captions, we only vary V_exp1 for halo 1 and V_exp2 for halo 2. The other physical parameters do not change. We use the parameters listed in Table 7. We always assume an intrinsic Lyα line with EW_int(Lyα) = 80 Å and FWHM_int(Lyα) = 150 km s^-1.