Relationship between 2D and 3D Galaxy Stellar Mass and Correlations with Halo Mass

TL;DR

This study uses simulated galaxies to compare how 2D and 3D stellar mass profiles relate to halo mass, finding that 2D projections are effective and do not introduce bias in weak lensing measurements.

Contribution

It demonstrates that 2D projected stellar mass profiles are comparable to 3D profiles in tracing halo mass and are effective for galaxy cluster identification.

Findings

2D and 3D stellar mass selections have similar halo mass proxy performance.

2D stellar mass selection sometimes outperforms 3D in correlation.

Lensing profiles of 2D and 3D selected samples are nearly identical.

Abstract

Recent studies suggest that the stars in the outer regions of massive galaxies trace halo mass better than the inner regions and that an annular stellar mass provides a low scatter method of selecting galaxy clusters. However, we can only observe galaxies as projected two-dimensional objects on the sky. In this paper, we use a sample of simulated galaxies to study how well galaxy stellar mass profiles in three dimensions correlate with halo mass, and what effects arise when observationally projecting stellar profiles into two dimensions. We compare 2D and 3D outer stellar mass selections and find that they have similar performance as halo mass proxies and that, surprisingly, a 2D selection sometimes has marginally better performance. We also investigate whether the weak lensing profiles around galaxies selected by 2D outer stellar mass suffer from projection effects. We find that the lensing profiles of samples selected by 2D and 3D definitions are nearly identical, suggesting that the 2D selection does not create a bias. These findings underscore the promise of using outer stellar mass as a tool for identifying galaxy clusters.