Direct Measurement of Galaxy Assembly Bias using DESI DR1 Data

TL;DR

This paper presents the first direct measurement of galaxy assembly bias using DESI DR1 data, employing a novel, cosmology-independent method combining group catalogs and weak lensing to analyze galaxy occupation dependence on large-scale environment.

Contribution

Introduces a new method to measure galaxy assembly bias directly from survey data, independent of cosmological assumptions, using group catalogs and weak lensing.

Findings

Measured the satellite galaxy assembly bias parameter as 0.05 ± 0.14, consistent with zero.

Demonstrated the method's robustness for future precision cosmology.

Found tension with many existing galaxy formation models.

Abstract

We report the first direct measurement of galaxy assembly bias, a critical systematic in cosmology, from the Dark Energy Spectroscopic Instrument (DESI) Bright Galaxy Survey. We introduce a novel, cosmology-independent method to measure the halo occupation distribution (HOD) by combining a state-of-the-art group catalog with weak gravitational lensing. For groups binned by total luminosity, we determine the galaxy occupation number $N_{\rm gal}$ from group-galaxy cross-correlations, while weak lensing constrains the average halo mass $M_h$. Applying this to a volume-limited sample at $z{\in}[0.05,0.2]$, we measure the dependence of HOD, $N_{\rm gal}(M_h)$, on large-scale overdensity $\delta_{g}$. Focusing on the satellite galaxies, we find an assembly bias parameter of $Q_{\rm sat}{=}0.05{\pm}0.14$, a result consistent with zero and in tension with many empirical galaxy formation models. Our method provides a robust approach for characterizing galaxy assembly bias to achieve precision cosmology with DESI and future Stage-V surveys.