The real-space correlation function measured from the APM Galaxy Survey

Abstract

We present a determination of the real space correlation function for galaxies in the APM Survey, with magnitudes in the range $17 < b_J < 20$. We recover a power law form for the correlation function $\xi(r) = (r/4.5)^{-1.7}$ on scales $r < 4 Mpc/h$, for a flat universe and clustering that is fixed in comoving coordinates.If we assume that clustering evolves according to linear perturbation theory, we obtain $\xi(r) = (r/5.25)^{-1.7}$. We recover a shoulder feature in $\xi(r)$ for scales $4 < r < 25 Mpc/h$, with the correlation function rising above the power law, before becoming consistent with zero around $r > 40 Mpc/h$. The form we obtain for $\xi(r)$ is smooth on large scales, allowing a determination of the distortions in the correlation function in redshift space, caused by the peculiar motions of galaxies to be made. Comparing the real space correlation function with the measurement of the redshift space correlation function by Loveday et al (1995), we find that a value for $omega^{0.6}/b$ (where $\omega$ is the density parameter of the universe and b is the bias factor between the density of light and mass) of unity is ruled out at the 2 sigma level.