A case devoid of bias : ORS voids vs . IRAS

We present a comparison between the voids in two nearly all sky redshift surveys: the ORS and the IRAS 1.2-Jy. While the galaxies in these surveys are selected differently and their populations are known to be biased relative to each other, the two void distributions are similar. We compare the spatial distribution of the two void populations and demonstrate the correlation between them. The voids also agree with regard to the overall void statistics – a filling factor of ≈ 0.45 of the volume, an average void diameter ¯ d void ≈ 45h −1 Mpc and an average galaxy underdensity in the voids ¯ δ ≈ −0.9. Our measurements of the underdensities of the voids in the two surveys enable us to estimate the relative bias in the voids between optical and IRAS samples. We find (b opt /b IRAS) void ≈ 1, showing that on average there is little – or no – biasing between the two void populations. Key words: cosmology: observations – galaxies: clustering – large-scale structure of the universe.