Constraining the luminous red galaxy halo occupation distribution using counts-in-cylinders

The low number density of the Sloan Digital Sky Survey (SDSS) luminous red galaxies (LRGs) suggests that LRGs occupying the same dark matter halo can be separated from pairs occupying distinct dark matter halos with high fidelity. We present a new technique, Counts-in-Cylinders (CiC), to constrain the parameters of the satellite contribution to the LRG halo occupation distribution once the parameters of the central galaxy contribution have been fixed. For a fiber-collision-corrected SDSS spectroscopic LRG subsample at 0.16 < z < 0.36, we find that the CiC multiplicity function is fitted by a halo model where the average number of satellites in a halo of mass M is <N _sat(M)> = ((M - M _cut)/M ₁) ^α with M _cut = 5.0^+1.5 _-1.3(^+2.9 _-2.6) × 10¹³ M, M ₁ = 4.95^+0.37 _-0.26(^+0.79 _-0.53) × 10¹⁴ M, and α = 1.035^+0.10 _-0.17(^+0.24 _-0.31) at the 68% and 95% confidence levels using a WMAP3 cosmology and z = 0.2 halo catalog. Our method tightly constrains the fraction of LRGs that are satellite galaxies, 6.36 ^+0.38 _-0.39%, and the combination M _cut/10 ¹⁴ M + α = 1.53^+0.08 _-0.09 at the 95% confidence level, though these constraints may be relaxed when cosmological parameters and the central galaxy parameters are allowed to vary simultaneously. We also find that mocks based on a halo catalog produced by a spherical overdensity finder reproduce both the measured CiC multiplicity function and the projected correlation function, while mocks based on a Friends-of-Friends halo catalog has a deficit of close pairs at 1 h ^-1 Mpc separations. Because the CiC method relies on higher order statistics of close pairs, it is robust to the choice of halo finder, and yields mock catalogs reproducing Finger-of-God (FOG) features in the observations probed by the CiC group multiplicity function. In a companion paper, we will apply this technique to optimize FOG compression to eliminate the one-halo contribution to the LRG power spectrum.