Modelling colour-dependent galaxy clustering in cosmological simulations

Abstract

We extend the subhalo abundance matching method to assign galaxy colour to subhaloes. We separate a luminosity-binned subhalo sample into two groups by a secondary subhalo property which is presumed to be correlated with galaxy colour. The two subsamples then represent red and blue galaxy populations. We explore two models for the secondary property, namely subhalo assembly time and local dark matter density around each subhalo. The model predictions for the galaxy two-point correlation functions are compared with the recent results from the Sloan Digital Sky Survey. We show that the observed colour dependence of galaxy clustering can be reproduced well by our method applied to cosmological N-body simulations without baryonic processes. We then compare the model predictions for the colour-dependent galaxy-mass cross-correlation functions with the results from gravitational lensing observations. The comparison allows us to distinguish the models, and also to discuss what subhalo property should be used to assign colour to subhaloes accurately. We show that the extended abundance matching method using the local dark matter density as a colour proxy provides an accurate description of the galaxy populations in the local universe. We also study impacts of scatter on the local dark matter density–colour relations. Introducing scatter improves agreements of our model predictions with the observed red and blue galaxy clustering and is needed to explain observed correlation functions in finer colour bins. Finally, we study red galaxy fraction profiles in galaxy group- and cluster-sized haloes and find that the red fraction profiles have a relatively strong dependence on our model parameters. We argue that the red fraction profiles can be an important observational clue, in addition to galaxy clustering and galaxy–galaxy lensing, to explore the galaxy–(sub)halo connections.