Luminous red galaxy clustering at z 0.7 – first results using AAOmega

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 3 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 hours 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 measured in ≈1.5hr exposures and present comparisons with 2SLAQ and COMBO-17 (photo-)redshifts. Crucially, the riz selection coupled with the 3-4× 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 maximising the S/N for the detection of the baryon acoustic oscillations (BAOs). Furthermore, we show that the amplitude of LRG clustering is s0 = 9.9± 0.7 h −1 Mpc, 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-peaks” model. We conclude that a redshift survey of 360 000 LRGs over 3000 deg, with an effective volume some 4× bigger than previously used to detect BAO with LRGs, is possible with AAOmega in 170 nights.