The local hole revealed by galaxy counts and redshifts

The redshifts of approximate to 250 000 galaxies are used to study the local hole and its associated peculiar velocities. The sample, compiled from the 6dF Galaxy Redshift Survey and Sloan Digital Sky Survey, provides wide sky coverage to a depth of approximate to 300 h(-1) Mpc. We have therefore examined K- and r-limited galaxy redshift distributions and number counts to map the local density field. Comparing observed galaxy n(z) distributions to homogeneous models in three large regions of the high-latitude sky, we find evidence for underdensities ranging from approximate to 4-40 per cent in these regions to depths of approximate to 150 h(-1) Mpc with the deepest underdensity being over the southern Galactic cap. Using the Galaxy and Mass Assembly survey, we then establish the normalization of galaxy counts at fainter magnitudes and thus confirm that the underdensity over all three fields at K < 12.5 is approximate to 15 +/- 3 per cent. Finally, we further use redshift catalogues to map sky-averaged peculiar velocities over the same areas using the average redshift-magnitude, (z) over bar (m), technique of Soneira. After accounting for the direct effect of the large-scale structure on (z) over bar (m) we can then search for peculiar velocities. Taking all three regions into consideration, the data reject at the approximate to 4 Sigma level the idea that we have recovered the cosmic microwave background rest frame in the volume probed. We therefore conclude that there is some consistent evidence from both counts and Hubble diagrams for a 'local hole' with an approximate to 150 h(-1) Mpc underdensity that deeper counts and redshifts in the northern Galactic cap suggest may extend to approximate to 300 h(-1) Mpc.