Environmental Effects on Real-Space and Redshift-Space Galaxy Clustering

TL;DR

This study examines how large-scale environmental effects influence galaxy clustering in both real and redshift space, using simulations and semi-analytic models to assess potential biases in cosmological measurements.

Contribution

It introduces a method to quantify environmental impacts on galaxy clustering and demonstrates their significance, especially for low-luminosity galaxy samples, with implications for modeling accuracy.

Findings

Environmental effects cause about 10% decrease in real-space 2PCF for low-luminosity galaxies.

Decomposition of 2PCF reveals age and richness dependence of halo clustering as key factors.

Neglecting environmental effects can lead to less than 6.5% systematic uncertainty in cosmological parameter estimation.

Abstract

Galaxy formation inside dark matter halos, as well as the halo formation itself, can be affected by large-scale environments. Evaluating the imprints of environmental effects on galaxy clustering is crucial for precise cosmological constraints with data from galaxy redshift surveys. We investigate such an environmental impact on both real-space and redshift-space galaxy clustering statistics using a semi-analytic model derived from the Millennium Simulation. We compare clustering statistics from original SAM galaxy samples and shuffled ones with environmental influence on galaxy properties eliminated. Among the luminosity-threshold samples examined, the one with the lowest threshold luminosity (~0.2L_*) is affected by environmental effects the most, which has a ~10% decrease in the real-space two-point correlation function (2PCF) after shuffling. By decomposing the 2PCF into five different components based on the source of pairs, we show that the change in the 2PCF can be explained by the age and richness dependence of halo clustering. The 2PCFs in redshift space are found to change in a similar manner after shuffling. If the environmental effects are neglected, halo occupation distribution modeling of the real-space and redshift-space clustering may have a less than 6.5% systematic uncertainty in constraining beta from the most affected SAM sample and have substantially smaller uncertainties from the other, more luminous samples. We argue that the effect could be even smaller in reality. In the Appendix, we present a method to decompose the 2PCF, which can be applied to measure the two-point auto-correlation functions of galaxy sub-samples in a volume-limited galaxy sample and their two-point cross-correlation functions in a single run utilizing only one random catalog.