On the Clustering of Faint Red Galaxies

TL;DR

This paper improves clustering measurements of faint red galaxies using a flux-limited sample, revealing their satellite nature in massive haloes and reducing uncertainties in large-scale clustering analysis.

Contribution

It introduces a method to enhance 2PCF measurements by utilizing flux-limited samples, leading to more accurate halo occupation modeling of faint red galaxies.

Findings

Faint red galaxies are predominantly satellites in massive haloes.

Improved measurements reduce large-scale clustering uncertainties by over 40%.

The satellite fraction is degenerate with the satellite distribution profile slope.

Abstract

Faint red galaxies in the Sloan Digital Sky Survey show a puzzling clustering pattern in previous measurements. In the two-point correlation function (2PCF), they appear to be strongly clustered on small-scales, indicating a tendency to reside in massive haloes as satellite galaxies. However, their weak clustering on large scales suggests that they are more likely to be found in low mass haloes. The interpretation of the clustering pattern suffers from the large sample variance in the 2PCF measurements, given the small volume of the volume-limited sample of such faint galaxies. We introduce a method to improve the clustering measurements of faint galaxies by making a full use of a flux-limited sample to obtain volume-limited measurements with an increased effective volume. In the improved 2PCF measurements, the fractional uncertainties on large-scales drop by more than 40 per cent, and the strong contrast between small-scale and large-scale clustering amplitudes seen in previous work is no longer prominent. From halo occupation distribution modelling of the measurements, we find that a considerable fraction of faint red galaxies to be satellites in massive haloes, a senario supported by the strong covariance of small-scale 2PCF measurements and the relative spatial distribution of faint red galaxies and luminous galaxies. However, the satellite fraction is found to be degenerate with the slope of the distribution profile of satellites in inner haloes. We compare the modelling results with semi-analytic model predictions and discuss the implications.