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We present multi-band photometry covering $\sim$ 5\deg $\times$ 5\deg across$\omega$ Cen collected with the Dark Energy Camera, combined to Hubble SpaceTelescope and Wide Field Imager data for the central regions. The unprecedentedphotometric accuracy and field coverage allowed us to confirm the differentspatial distribution of blue and red main-sequence stars, and of red-giantbranch (RGB) stars with different metallicities. The ratio of the number ofblue to red main-sequence stars shows that the blue main-sequencesub-population has a more extended spatial distribution compared to the redmain-sequence one, and the frequency of blue main-sequence stars increases at adistance of $\sim$ 20 arcmin from $\omega$ Cen center. Similarly, the moremetal-rich RGB stars show a more extended spatial distribution compared to themore metal-poor ones in the outskirts of the cluster. Moreover, the centers ofthe distributions of metal-rich and metal-poor RGB stars are shifted indifferent directions with respect to the geometrical center of $\omega$ Cen. Weconstructed stellar density profiles for the blue and red main-sequence stars;they confirm that the blue main-sequence sub-population has a more extendedspatial distribution compared to the red main-sequence one in the outskirts of$\omega$ Cen, as found based on the star number ratio. We also computed theellipticity profile of $\omega$ Cen, which has a maximum value of 0.16 at adistance of $\sim$ 8 arcmin from the center, and a minimum of 0.05 at $\sim$ 30arcmin; the average ellipticity is $\sim0.10$. The circumstantial evidencepresented in this work suggests a merging scenario for the formation of thepeculiar stellar system $\omega$ Cen.

The not so simple stellar system Omega Cen. II. Evidence in support of a merging scenario