Optical dipole anisotropy

The large-scale distribution of light is illustrated by maps of about 15 000 optical galaxies. The maps are based on the UGC, ESO and MCG catalogues. The combined catalogue has an isophotal diameter limit and covers the entire sky, except for obscured regions. The dipole anisotropy in the galaxy distribution points towards |l= 227^ 23^, \, b= 42^ 8^|⁠, a direction which is not sensitive to Galactic obscurations. In this calculation each galaxy is weighted by the square of its angular diameter and only non Local Group galaxies are counted. The optical dipole is about 37° from the microwave background radiation dipole and about 10° from the IRAS dipole. The rough alignment of the three dipoles suggests that light traces mass. The average depth of the catalogue is estimated to be 50 h–1 Mpc (where |H₀ =100 \, h\, km\, s^-1\, Mpc^-1| and the density parameter is roughly |₀0. 3|⁠.