Analytical halo model of galactic conformity

TL;DR

This paper develops an analytical halo model to describe galaxy colour-dependent clustering, incorporating galactic conformity effects through a correlation between galaxy colour and halo concentration, validated against mock catalogs and SDSS data.

Contribution

It introduces a fully analytical model of galactic conformity within the halo occupation distribution framework, including both 1-halo and 2-halo conformity effects, validated with empirical data.

Findings

Model achieves 10-20% accuracy in clustering predictions.

Good agreement with SDSS data for 1-halo conformity levels.

No strong evidence for 2-halo conformity driven by assembly bias.

Abstract

We present a fully analytical halo model of colour-dependent clustering that incorporates the effects of galactic conformity in a halo occupation distribution (HOD) framework. The model, based on our previous numerical work, describes conformity through a correlation between the colour of a galaxy and the concentration of its parent halo, leading to a correlation between central and satellite galaxy colours at fixed halo mass. The strength of the correlation is set by a tunable `group quenching efficiency', and the model can separately describe group-level correlations between galaxy colour (1-halo conformity) and large scale correlations induced by assembly bias (2-halo conformity). We validate our analytical results using clustering measurements in mock galaxy catalogs, finding that the model is accurate at the 10-20 percent level for a wide range of luminosities and length scales. We apply the formalism to interpret the colour-dependent clustering of galaxies in the Sloan Digital Sky Survey (SDSS). We find good overall agreement between the data and a model that has 1-halo conformity at a level consistent with previous results based on an SDSS group catalog, although the clustering data require satellites to be redder than suggested by the group catalog. Within our modelling uncertainties, however, we do not find strong evidence of 2-halo conformity driven by assembly bias in SDSS clustering.