2008MNRAS.387.1323R

We report on the AAT-AAOmega LRG Pilot observing run to establish the feasibility of a large spectroscopic survey using the new AAOmega instrument. We have selected luminous red galaxies (LRGs) using single epoch SDSS riz-photometry to i < 20.5 and z < 20.2. We have observed in three fields including the COSMOS field and the COMBO-17 S11 field, obtaining a sample of ∼600 redshift z ≳ 0.5 LRGs. Exposure times varied from 1-4 h to determine the minimum exposure for AAOmega to make an essentially complete LRG redshift survey in average conditions. We show that LRG redshifts to i < 20.5 can be measured in ~1.5h exposures and present comparisons with 2SLAQ and COMBO-17 (photo)redshifts. Crucially, the riz selection coupled with the three to four times improved AAOmega throughput is shown to extend the LRG mean redshift from z = 0.55 for 2SLAQ to z = 0.681±0.005 for riz-selected LRGs. This extended range is vital for maximizing the signal-to-noise ratio for the detection of the baryon acoustic oscillations (BAOs). Furthermore, we show that the amplitude of LRG clustering is s₀= 9.9±0.7h^–1Mpc, as high as that seen in the 2SLAQ LRG Survey. Consistent results for this clustering amplitude are found from the projected and semi-projected correlation functions. This high amplitude is consistent with a long-lived population whose bias evolves as predicted by a simple `high-peak' model. We conclude that a redshift survey of 360000 LRGs over 3000 deg², with an effective volume some four times bigger than previously used to detect BAO with LRGs, is possible with AAOmega in 170 nights.