Citation:
Date Published:
October 1, 2007Abstract:
We present a clustering analysis of luminous red galaxies (LRGs) usingnearly 9000 objects from the final, three-year catalogue of the 2dF-SDSSLRG and QSO (2SLAQ) Survey. We measure the redshift-space two-pointcorrelation function, ξ(s) and find that, at the mean LRG redshift ofshows the characteristic downturn at small scales(<~1h-1Mpc) expected from line-of-sight velocitydispersion. We fit a double power law to ξ(s) and measure anamplitude and slope of s0 =17.3+2.5-2.0h-1Mpc,γ = 1.03 +/-0.07 at small scales (s < 4.5h-1Mpc) and s0 =9.40 +/- 0.19h-1Mpc,γ = 2.02 +/- 0.07 at large scales(s > 4.5h-1Mpc). In the semiprojected correlationfunction, wp(σ), we find a simple power law withγ = 1.83 +/- 0.05 and r0 = 7.30 +/-0.34h-1Mpc fits the data in the range 0.4 < σ <50h-1Mpc, although there is evidence of a steeper power lawat smaller scales. A single power law also fits the deprojectedcorrelation function ξ(r), with a correlation length of r0= 7.45 +/- 0.35h-1Mpc and a power-law slope of γ = 1.72+/- 0.06 in the 0.4 < r < 50h-1Mpc range. But it is inthe LRG angular correlation function that the strongest evidence fornon-power-law features is found where a slope of γ = -2.17 +/-0.07 is seen at 1 < r < 10h-1Mpc with a flatter γ= -1.67 +/- 0.07 slope apparent at r <~ 1h-1Mpc scales.We use the simple power-law fit to the galaxy ξ(r), under theassumption of linear bias, to model the redshift-space distortions inthe 2D redshift-space correlation function, ξ(σ, π). We fitfor the LRG velocity dispersion, wz, the density parameter,Ωm and β(z), where β(z) =Ω0.6m/b and b is the linear bias parameter.We find values of wz =330kms-1,Ωm =0.10+0.35-0.10 and β = 0.40 +/- 0.05. The lowvalues for wz and β reflect the high bias of the LRGsample. These high-redshift results, which incorporate theAlcock-Paczynski effect and the effects of dynamical infall, start tobreak the degeneracy between Ωm and β found inlow-redshift galaxy surveys such as 2dFGRS. This degeneracy is furtherbroken by introducing an additional external constraint, which is thevalue β(z = 0.1) = 0.45 from 2dFGRS, and then considering theevolution of clustering from z ~ 0 to zLRG ~ 0.55. With thesecombined methods we find Ωm(z = 0) = 0.30 +/- 0.15 andβ(z = 0.55) = 0.45 +/- 0.05. Assuming these values, we find a valuefor b(z = 0.55) = 1.66 +/- 0.35. We show that this is consistent with asimple `high-peak' bias prescription which assumes that LRGs have aconstant comoving density and their clustering evolves purely undergravity.