Observational Measures of Halo Properties Beyond Mass

TL;DR

This paper explores how galaxy environment measurements can reveal underlying dark matter halo properties, demonstrating distinct environmental signatures in galaxy clustering that can test and refine galaxy formation models.

Contribution

It introduces a method to infer dark matter halo properties from galaxy environment measurements and tests galaxy size models against observational clustering data.

Findings

Distinct environmental signatures for halo properties beyond mass.

Classic galaxy size models show tension with SDSS data.

A simple model correlating galaxy size with halo growth improves fit.

Abstract

Different properties of dark matter haloes, including growth rate, concentration, interaction history, and spin, correlate with environment in unique, scale-dependent ways. While these halo properties are not directly observable, galaxies will inherit their host haloes' correlations with environment. In this paper, we show how these characteristic environmental signatures allow using measurements of galaxy environment to constrain which dark matter halo properties are most tightly connected to observable galaxy properties. We show that different halo properties beyond mass imprint distinct scale-dependent signatures in both the galaxy two-point correlation function and the distribution of distances to galaxies' $k$th nearest neighbours, with features strong enough to be accessible even with low-resolution (e.g., grism) spectroscopy at higher redshifts. As an application, we compute observed two-point correlation functions for galaxies binned by half-mass radius at $z=0$ from the Sloan Digital Sky Survey, showing that classic galaxy size models (i.e., galaxy size being proportional to halo spin) as well as other recent proposals show significant tensions with observational data. We show that the agreement with observed clustering can be improved with a simple empirical model in which galaxy size correlates with halo growth.