Modeling the Very Small-Scale Clustering of Luminous Red Galaxies

TL;DR

This paper models the small-scale clustering of luminous red galaxies using halo occupation distribution formalism, revealing that their satellite distribution is closer to isothermal rather than following the dark matter profile.

Contribution

It introduces a flexible density profile model for satellite LRGs, showing the inner slope differs from the dark matter NFW profile, improving clustering fits.

Findings

Satellite LRG distribution is closer to isothermal.

Varying P(N|M) alone does not fit small-scale data.

Allowing the inner slope to vary yields a good fit.

Abstract

We model the small-scale clustering of luminous red galaxies (LRGs; Masjedi et al. 2006) in the Sloan Digital Sky Survey (SDSS). Specifically, we use the halo occupation distribution (HOD) formalism to model the projected two-point correlation function of LRGs on scales well within the sizes of their host halos (0.016 Mpc/h < r < 0.42 Mpc/h). We start by varying P(N|M), the probability distribution that a dark matter halo of mass M contains N LRGs, and assuming that the radial distribution of satellite LRGs within halos traces the NFW dark matter density profile. We find that varying P(N|M) alone is not sufficient to match the small-scale data. We next allow the concentration of satellite LRG galaxies to differ from that of dark matter and find that this is also not sufficient. Finally, we relax the assumption of an NFW profile and allow the inner slope of the density profile to vary. We find that this model provides a good fit to the data and the resulting value of the slope is -2.17 +/- 0.12. The radial density profile of satellite LRGs within halos is thus not compatible with that of the underlying dark matter, but rather is closer to an isothermal distribution.