Strong bimodality in the host halo mass of central galaxies from galaxy–galaxy lensing

Rachel Mandelbaum,Ying Zu,Bruno Henriques,Simon White,Surhud More,Wenting Wang

doi:10.1093/mnras/stw188

Abstract

We use galaxy-galaxy lensing to study the dark matter halos surrounding a sample of Locally Brightest Galaxies (LBGs) selected from the Sloan Digital Sky Survey. We measure mean halo mass as a function of the stellar mass and colour of the central galaxy. Mock catalogues constructed from semi-analytic galaxy formation simulations demonstrate that most LBGs are the central objects of their halos, greatly reducing interpretation uncertainties due to satellite contributions to the lensing signal. Over the full stellar mass range, $10.3 < \log [M_*/M_\odot] < 11.6$, we find that passive central galaxies have halos that are at least twice as massive as those of star-forming objects of the same stellar mass. The significance of this effect exceeds $3\sigma$ for $\log [M_*/M_\odot] > 10.7$. Tests using the mock catalogues and on the data themselves clarify the effects of LBG selection and show that it cannot artificially induce a systematic dependence of halo mass on LBG colour. The bimodality in halo mass at fixed stellar mass is reproduced by the astrophysical model underlying our mock catalogue, but the sign of the effect is inconsistent with recent, nearly parameter-free age-matching models. The sign and magnitude of the effect can, however, be reproduced by halo occupation distribution models with a simple (few-parameter) prescription for type-dependence.

Highlights

Galaxies are often classified as passive or active1, where passive galaxies typically have a red rest-frame color indicative of a paucity of recent star formation, and active galaxies have bluer colors indicating recent and/or ongoing star formation
Where the summation is carried out over bins in rp. This test is interesting when the stellar mass distribution for red and blue Locally Brightest Galaxies (LBGs) within the bin is sufficiently similar that differences in ∆Σ cannot come just from the different stellar mass distribution
To validate the relatively simple interpretation of these lensing signals in terms of average halo masses, we have used both simulation-based mock catalogs that closely reproduce the observed properties of Main sample galaxies and LBGs, and cross-checks within the observational dataset itself

Summary

Introduction

Galaxies are often classified as passive or active, where passive galaxies typically have a red rest-frame color indicative of a paucity of recent star formation, and active galaxies have bluer colors indicating recent and/or ongoing star formation. Semi-analytic models (SAMs) applied to subhalo catalogs from N -body simulations (as early as Kauffmann et al 1997; see Guo et al 2011; Benson 2012 for more recent examples) and hydrodynamic simulations (e.g., Vogelsberger et al 2014; Khandai et al 2015; Schaye et al 2015) predict a potentially quite complicated and physically-based relation between the galaxies and their dark matter halos, including a properly self-consistent treatment of the time evolution of this relationship In both cases, there are parameters that must be tuned to match observations. The age-matching technique (Hearin & Watson 2013; Hearin et al 2014) can be applied to catalogs from an N -body simulation, and assumes (rather than predicting) a particular relationship between the masses and ages of galaxies and those of their halos in order to populate the halos with galaxies

Methods

Results

Conclusion