Dipole Anisotropy in Newly Sampled AGN Population: Still in Tension with CMB Dipole

Abstract

We revisit the all-sky survey data, the Wide-field Infrared Survey Explorer (WISE) catalog, with an improved galaxy-selection criterion to investigate the inconsistency between the dipole anisotropy in the galaxy number count and the kinematic CMB dipole anisotropy. We apply a set of active galactic nuclei (AGN) selection criteria composed of a flux cut and multiple color cuts, and formulate an appropriate adaptation of the original Ellis & Baldwin (1984) formalism for our photometric survey samples whose spectral energy distributions deviate from a pure power-law form. We find that the newly sampled AGNs from the WISE catalog still bears an anomalous number-count dipole anisotropy, whose amplitude is ~ 2.5 times as large as that of the purely kinematic origin at a 5.3 sigma confidence level. We also find that the direction of our WISE-AGN dipole is ~ 3 sigma away from that of the CMB dipole. We discuss its possible cosmological implications: nonlinearity of the nearby universe and mismatch of matter-rest frame and the CMB-rest frame.