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The spatial fluctuations in the tomographic maps of the redshifted 21-cmsignal from the Cosmic Dawn (CD) crucially depend on the size and distributionof the regions with gas temperatures larger than the radio backgroundtemperature. In this article, we study the morphological characteristics ofsuch emission regions and their absorption counterparts using the shapediagnostic tool {\sc surfgen2}. Using simulated CD brightness temperature cubesof the 21-cm signal, we find that the emission regions percolate at stages withthe filling factor of the emission regions $FF_{\rm emi}\gtrsim 0.15$.Percolation of the absorption regions occurs for $FF_{\rm abs}\gtrsim 0.05$.The largest emission and absorption regions are topologically complex andhighly filamentary for most parts of the CD. The number density of theseregions as a function of the volume shows the power-law nature with thepower-law indexes $\approx -2$ and $-1.6$ for the emission and absorptionregions, respectively. Overall, the planarity, filamentarity and genus increasewith the increase of the volume of both emission and absorption regions.

The morphology of the redshifted 21-cm signal from the Cosmic Dawn