Galaxy-galaxy weak-lensing measurement from SDSS: II. host halo properties of galaxy groups

TL;DR

This study measures and models galaxy-galaxy lensing signals around galaxy groups in SDSS DR7, identifying the brightest central galaxy as the best halo-center tracer and deriving halo properties through comprehensive modeling and MCMC analysis.

Contribution

It provides a detailed lensing-based analysis of galaxy group halo properties, comparing different halo-center tracers and modeling off-centered profiles with a multi-component approach.

Findings

BCGs are the best halo-center tracers among candidates.

Lensing-derived halo masses agree with abundance matching results, except at the lowest masses.

The modeling constrains halo mass, concentration, off-centering, and subhalo properties.

Abstract

As the second paper of a series on studying galaxy-galaxy lensing signals using the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), we present our measurement and modelling of the lensing signals around groups of galaxies. We divide the groups into four halo mass bins, and measure the signals around four different halo-center tracers: brightest central galaxy (BCG), luminosity-weighted center, number-weighted center and X-ray peak position. For X-ray and SDSS DR7 cross identified groups, we further split the groups into low and high X-ray emission subsamples, both of which are assigned with two halo-center tracers, BCGs and X-ray peak positions. The galaxy-galaxy lensing signals show that BCGs, among the four candidates, are the best halo-center tracers. We model the lensing signals using a combination of four contributions: off-centered NFW host halo profile, sub-halo contribution, stellar contribution, and projected 2-halo term. We sample the posterior of 5 parameters i.e., halo mass, concentration, off-centering distance, sub halo mass, and fraction of subhalos via a MCMC package using the galaxy-galaxy lensing signals. After taking into account the sampling effects (e.g. Eddington bias), we found the best fit halo masses obtained from lensing signals are quite consistent with those obtained in the group catalog based on an abundance matching method, except in the lowest mass bin. Subject headings: (cosmology:) gravitational lensing, galaxies: clusters: general