Speaker
Description
We study the angular distribution of the exponent $(\rm x)$ of the differential number counts $\rm n(S) = \big(\frac{\rm d^{2}N}{\rm dSd\Omega}\big)\propto \rm S^{-1-x}$, i.e., number of quasars per unit solid angle per unit flux density $(\rm S)$, employing the CatWISES2020 catalog. We find the dipole anisotropy in this parameter with dipole amplitude $0.005\pm0.002$ and direction points towards $(201.50^{\circ} \pm 27.87^{\circ}, -29.37^{\circ} \pm 19.86^{\circ})$ in the Galactic coordinate system. Interestingly, this dipole anisotropy direction very close to the hemispherical power asymmetry direction $(l,b)=(221^\circ,-27^{\circ})$ in the cosmic microwave background (CMB) radiations. The signal is found to be absent for low flux density sources and arises primarily from sources of higher flux density which may be less affected by observational bias. Next we extract the dipole anisotropy in number counts in various color bins. It is found that the dipole signal differs significantly in two color bins, namely, $1.1>W1-W2\ge 0.8$ and $1.4>W1-W2>1.1$. The color bin $1.4>W1-W2>1.1$ appears strongly contaminated, with possibly Galactic contributions and is unreliable for extracting the signal of cosmological dipole. The source of this contamination has not been identified and cannot be attributed to known emissions within the galaxy. Removing this contaminated color bin leads to a strong dipole signal with a direction significantly different from that obtained from full data. If we interpret this dipole as due to our local motion, the extracted velocity turns out to be $900\pm 113$ Kms$^{-1}$, which deviates from the CMB dipole velocity with approximately $4.7$ sigma significance.
