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tokens: between the individual patterns. The middle panel of Fig. 9 shows the δ T b map at redshift 16. The number of sources drops quite drastically in this frequency channel as we are probing the initial stages of the cosmic dawn. The overlap between the individual patterns too is not that substantial. The decrease in the number of sources towards the lower frequency channels can be seen from the right-hand panel of Fig. 9 , where we show the light cone from our simulation box. The signal at the higher frequency end of the box is essentially the strong absorption signal arising from the significant overlap between the Ly α photons from the sources. Note that we have subtracted the mean from each frequency channel while making the image and thus the signal is a combination of emission and absorption regions. As the signals from the channels corresponding to redshifts 15 and 16 are dominated by the absorption regions, the mean of the expected signal is negative. The regions with positive values of the signal in the left-hand and middle panels of Fig. 9 arise because of subtracting the mean signal from the maps. In reality, these are the Ly α-deficient regions with almost no 21 cm signal. Figure 9. Left-hand panel: 24 × 24 map of the 21 cm signal (without smoothing) at the frequency channel ν c = 89 MHz generated from the simulation using the N -body simulation and a one-dimensional radiative transfer code. The ‘×’ marks represent the angular positions of the sources between a band ν c − 0.1 to ν c + 0.1 MHz. Middle panel: same as the left-hand panel, but at the frequency channel corresponding to ν = 84 MHz. Right-hand panel: the light-cone map of δ T b distribution. The arrows in the top label of the panel show the frequency channels corresponding to the maps in the left-hand and middle panels. The maps include the effect of redshift-space distortion and the light-cone effect. The top-left panel of Fig. 10 shows the smoothed image of the residual signal and noise at the central frequency channel after subtracting the foregrounds using the polynomial method. The noise in the panel corresponds to 200 h of observation, and the smoothing is performed using the Gaussian filter of size 30 arcmin. One can easily identify that even in the smoothed map, the signal is localized around the sources. The top-right panel of Fig. 10 shows the same but for 2000 h of observation. The SNRs of these top-left and top-right panels are 4.8 and 14.2, respectively. The bottom-left and bottom-right panels are the same as the top panels but at a different frequency channel corresponding to ν = 84 MHz ( z = 16). The corresponding SNRs in the bottom panels are 3.3 and 10.1, respectively. The Pearson cross-correlation coefficients χ, in this case, are given in Table 3 . We find that the foreground subtraction method works effectively in this case as well leading to reasonably high values of χ. Figure 10. Top-left panel: map of the residual signal and noise after foreground