  In this study, we are going to discuss the accelerated expansion of the
universe and how this accelerated expansion affects the paths of photons from
cosmic microwave background radiation (CMB). Then we will see how wide-field
galaxy surveys along with cosmic CMB anisotropy maps can help us in studying
dark energy. The cross-correlation of galaxy over/under-density maps with CMB
anisotropy maps help us in measuring one of the most useful signatures of dark
energy i.e. Integrated Sachs-Wolfe (ISW) effect. ISW effect explains the
blue-shifting and red-shifting of CMB photons when they reach to us after
passing through large scale structures and super-voids respectively. We will
look into the theoretical foundations behind ISW effect and discuss how modern
all sky galaxy surveys like EMU-ASKAP will be useful in studying the effect.
