Regarding the line-of-sight baryonic acoustic feature in the Sloan Digital Sky Survey and baryon Oscillation Spectroscopic Survey luminous red galaxy samples

We analyze the line-of-sight baryonic acoustic feature in the two-point correlation function ξ of the Sloan Digital Sky Survey luminous red galaxy (LRG) sample (0.16 < z < 0.47). By defining a narrow line-of-sight region, rp < 5.5 h^-1 Mpc, where r_p is the transverse separation component, we measure a strong excess of clustering at ∼110 h^-1 Mpc, as previously reported in the literature. We also test these results in an alternative coordinate system, by defining the line of sight as θ < 3° where θ is the opening angle. This clustering excess appears much stronger than the feature in the better-measured monopole. A fiducial ACDM nonlinear model in redshift space predicts a much weaker signature. We use realistic mock catalogs to model the expected signal and noise. We find that the line-of-sight measurements can be explained well by our mocks as well as by a featureless ξ = 0. We conclude that there is no convincing evidence that the strong clustering measurement is the line-of-sight baryonic acoustic feature. We also evaluate how detectable such a signal would be in the upcoming Baryon Oscillation Spectroscopic Survey (BOSS) LRG volume. Mock LRG catalogs (z < 0.6) suggest that (1) the narrow line-of-sight cylinder and cone defined above probably will not reveal a detectable acoustic feature in BOSS; (2) a clustering measurement as high as that in the current sample can be ruled out (or confirmed) at a high confidence level using a BOSS-sized data set; (3) an analysis with wider angular cuts, which provide better signal-to-noise ratios, can nevertheless be used to compare line-of-sight and transverse distances, and thereby constrain the expansion rate H(z) and diameter distance DA(z).